diff --git a/spec/MockStorageApi.js b/spec/MockStorageApi.js
index 691fccf3a..1063ad3db 100644
--- a/spec/MockStorageApi.js
+++ b/spec/MockStorageApi.js
@@ -40,8 +40,8 @@ MockStorageApi.prototype = {
         return this.keys[index];
     },
     _recalc: function() {
-        let keys = [];
-        for (let k in this.data) {
+        const keys = [];
+        for (const k in this.data) {
             if (!this.data.hasOwnProperty(k)) {
                 continue;
             }
diff --git a/spec/integ/matrix-client-crypto.spec.js b/spec/integ/matrix-client-crypto.spec.js
index 87262c57a..a09008ef3 100644
--- a/spec/integ/matrix-client-crypto.spec.js
+++ b/spec/integ/matrix-client-crypto.spec.js
@@ -1,21 +1,21 @@
 "use strict";
-let sdk = require("../..");
-let q = require("q");
-let HttpBackend = require("../mock-request");
-let utils = require("../../lib/utils");
-let testUtils = require("../test-utils");
+const sdk = require("../..");
+const q = require("q");
+const HttpBackend = require("../mock-request");
+const utils = require("../../lib/utils");
+const testUtils = require("../test-utils");
 
 let aliHttpBackend;
 let bobHttpBackend;
 let aliClient;
-let roomId = "!room:localhost";
-let aliUserId = "@ali:localhost";
-let aliDeviceId = "zxcvb";
-let aliAccessToken = "aseukfgwef";
+const roomId = "!room:localhost";
+const aliUserId = "@ali:localhost";
+const aliDeviceId = "zxcvb";
+const aliAccessToken = "aseukfgwef";
 let bobClient;
-let bobUserId = "@bob:localhost";
-let bobDeviceId = "bvcxz";
-let bobAccessToken = "fewgfkuesa";
+const bobUserId = "@bob:localhost";
+const bobDeviceId = "bvcxz";
+const bobAccessToken = "fewgfkuesa";
 let bobOneTimeKeys;
 let aliDeviceKeys;
 let bobDeviceKeys;
@@ -38,8 +38,8 @@ let bobMessages;
  * {one_time_keys: {}, device_keys: {}}
  */
 function expectKeyUpload(deviceId, httpBackend) {
-    let uploadPath = "/keys/upload/" + deviceId;
-    let keys = {};
+    const uploadPath = "/keys/upload/" + deviceId;
+    const keys = {};
 
     httpBackend.when("POST", uploadPath).respond(200, function(path, content) {
         expect(content.one_time_keys).not.toBeDefined();
@@ -53,7 +53,7 @@ function expectKeyUpload(deviceId, httpBackend) {
         expect(content.one_time_keys).toBeDefined();
         expect(content.one_time_keys).not.toEqual({});
         let count = 0;
-        for (let key in content.one_time_keys) {
+        for (const key in content.one_time_keys) {
             if (content.one_time_keys.hasOwnProperty(key)) {
                 count++;
             }
@@ -119,11 +119,11 @@ function expectAliQueryKeys() {
     // can't query keys before bob has uploaded them
     expect(bobDeviceKeys).toBeDefined();
 
-    let bobKeys = {};
+    const bobKeys = {};
     bobKeys[bobDeviceId] = bobDeviceKeys;
     aliHttpBackend.when("POST", "/keys/query").respond(200, function(path, content) {
         expect(content.device_keys[bobUserId]).toEqual({});
-        let result = {};
+        const result = {};
         result[bobUserId] = bobKeys;
         return {device_keys: result};
     });
@@ -139,11 +139,11 @@ function expectBobQueryKeys() {
     // can't query keys before ali has uploaded them
     expect(aliDeviceKeys).toBeDefined();
 
-    let aliKeys = {};
+    const aliKeys = {};
     aliKeys[aliDeviceId] = aliDeviceKeys;
     bobHttpBackend.when("POST", "/keys/query").respond(200, function(path, content) {
         expect(content.device_keys[aliUserId]).toEqual({});
-        let result = {};
+        const result = {};
         result[aliUserId] = aliKeys;
         return {device_keys: result};
     });
@@ -160,7 +160,7 @@ function expectAliClaimKeys() {
     expect(bobOneTimeKeys).toBeDefined();
 
     aliHttpBackend.when("POST", "/keys/claim").respond(200, function(path, content) {
-        let claimType = content.one_time_keys[bobUserId][bobDeviceId];
+        const claimType = content.one_time_keys[bobUserId][bobDeviceId];
         expect(claimType).toEqual("signed_curve25519");
         let keyId = null;
         for (keyId in bobOneTimeKeys) {
@@ -170,7 +170,7 @@ function expectAliClaimKeys() {
                 }
             }
         }
-        let result = {};
+        const result = {};
         result[bobUserId] = {};
         result[bobUserId][bobDeviceId] = {};
         result[bobUserId][bobDeviceId][keyId] = bobOneTimeKeys[keyId];
@@ -185,7 +185,7 @@ function aliDownloadsKeys() {
     // can't query keys before bob has uploaded them
     expect(bobDeviceEd25519Key).toBeDefined();
 
-    let p1 = aliClient.downloadKeys([bobUserId]).then(function() {
+    const p1 = aliClient.downloadKeys([bobUserId]).then(function() {
         expect(aliClient.listDeviceKeys(bobUserId)).toEqual([{
             id: "bvcxz",
             key: bobDeviceEd25519Key,
@@ -194,12 +194,12 @@ function aliDownloadsKeys() {
             display_name: null,
         }]);
     });
-    let p2 = expectAliQueryKeys();
+    const p2 = expectAliQueryKeys();
 
     // check that the localStorage is updated as we expect (not sure this is
     // an integration test, but meh)
     return q.all([p1, p2]).then(function() {
-        let devices = aliStorage.getEndToEndDevicesForUser(bobUserId);
+        const devices = aliStorage.getEndToEndDevicesForUser(bobUserId);
         expect(devices[bobDeviceId].keys).toEqual(bobDeviceKeys.keys);
         expect(devices[bobDeviceId].verified).
             toBe(0); // DeviceVerification.UNVERIFIED
@@ -279,7 +279,7 @@ function expectAliSendMessageRequest() {
     return expectSendMessageRequest(aliHttpBackend).then(function(content) {
         aliMessages.push(content);
         expect(utils.keys(content.ciphertext)).toEqual([bobDeviceCurve25519Key]);
-        let ciphertext = content.ciphertext[bobDeviceCurve25519Key];
+        const ciphertext = content.ciphertext[bobDeviceCurve25519Key];
         expect(ciphertext).toBeDefined();
         return ciphertext;
     });
@@ -293,10 +293,10 @@ function expectAliSendMessageRequest() {
 function expectBobSendMessageRequest() {
     return expectSendMessageRequest(bobHttpBackend).then(function(content) {
         bobMessages.push(content);
-        let aliKeyId = "curve25519:" + aliDeviceId;
-        let aliDeviceCurve25519Key = aliDeviceKeys.keys[aliKeyId];
+        const aliKeyId = "curve25519:" + aliDeviceId;
+        const aliDeviceCurve25519Key = aliDeviceKeys.keys[aliKeyId];
         expect(utils.keys(content.ciphertext)).toEqual([aliDeviceCurve25519Key]);
-        let ciphertext = content.ciphertext[aliDeviceCurve25519Key];
+        const ciphertext = content.ciphertext[aliDeviceCurve25519Key];
         expect(ciphertext).toBeDefined();
         return ciphertext;
     });
@@ -309,7 +309,7 @@ function sendMessage(client) {
 }
 
 function expectSendMessageRequest(httpBackend) {
-    let path = "/send/m.room.encrypted/";
+    const path = "/send/m.room.encrypted/";
     let sent;
     httpBackend.when("PUT", path).respond(200, function(path, content) {
         sent = content;
@@ -323,17 +323,17 @@ function expectSendMessageRequest(httpBackend) {
 }
 
 function aliRecvMessage() {
-    let message = bobMessages.shift();
+    const message = bobMessages.shift();
     return recvMessage(aliHttpBackend, aliClient, bobUserId, message);
 }
 
 function bobRecvMessage() {
-    let message = aliMessages.shift();
+    const message = aliMessages.shift();
     return recvMessage(bobHttpBackend, bobClient, aliUserId, message);
 }
 
 function recvMessage(httpBackend, client, sender, message) {
-    let syncData = {
+    const syncData = {
         next_batch: "x",
         rooms: {
             join: {
@@ -354,8 +354,8 @@ function recvMessage(httpBackend, client, sender, message) {
         },
     };
     httpBackend.when("GET", "/sync").respond(200, syncData);
-    let deferred = q.defer();
-    let onEvent = function(event) {
+    const deferred = q.defer();
+    const onEvent = function(event) {
         console.log(client.credentials.userId + " received event",
                     event);
 
@@ -388,7 +388,7 @@ function aliStartClient() {
     // ali will try to query her own keys on start
     aliHttpBackend.when("POST", "/keys/query").respond(200, function(path, content) {
         expect(content.device_keys[aliUserId]).toEqual({});
-        let result = {};
+        const result = {};
         result[aliUserId] = {};
         return {device_keys: result};
     });
@@ -405,7 +405,7 @@ function bobStartClient() {
     // bob will try to query his own keys on start
     bobHttpBackend.when("POST", "/keys/query").respond(200, function(path, content) {
         expect(content.device_keys[bobUserId]).toEqual({});
-        let result = {};
+        const result = {};
         result[bobUserId] = {};
         return {device_keys: result};
     });
@@ -429,7 +429,7 @@ function startClient(httpBackend, client) {
     httpBackend.when("POST", "/filter").respond(200, { filter_id: "fid" });
 
     // send a sync response including our test room.
-    let syncData = {
+    const syncData = {
         next_batch: "x",
         rooms: {
             join: { },
@@ -510,11 +510,11 @@ describe("MatrixClient crypto", function() {
                 },
             });
 
-            let p1 = aliClient.downloadKeys(['@bob:id']);
-            let p2 = aliHttpBackend.flush('/keys/query', 1);
+            const p1 = aliClient.downloadKeys(['@bob:id']);
+            const p2 = aliHttpBackend.flush('/keys/query', 1);
 
             q.all([p1, p2]).then(function() {
-                let devices = aliStorage.getEndToEndDevicesForUser('@bob:id');
+                const devices = aliStorage.getEndToEndDevicesForUser('@bob:id');
                 expect(utils.keys(devices).length).toEqual(0);
 
                 // request again: should be no more requests
@@ -555,9 +555,9 @@ describe("MatrixClient crypto", function() {
     });
 
     it("Ali gets keys with an incorrect userId", function(done) {
-        let eveUserId = "@eve:localhost";
+        const eveUserId = "@eve:localhost";
 
-        let bobDeviceKeys = {
+        const bobDeviceKeys = {
             algorithms: ['m.olm.v1.curve25519-aes-sha2', 'm.megolm.v1.aes-sha2'],
             device_id: 'bvcxz',
             keys: {
@@ -573,10 +573,10 @@ describe("MatrixClient crypto", function() {
             },
         };
 
-        let bobKeys = {};
+        const bobKeys = {};
         bobKeys[bobDeviceId] = bobDeviceKeys;
         aliHttpBackend.when("POST", "/keys/query").respond(200, function(path, content) {
-            let result = {};
+            const result = {};
             result[bobUserId] = bobKeys;
             return {device_keys: result};
         });
@@ -592,7 +592,7 @@ describe("MatrixClient crypto", function() {
     });
 
     it("Ali gets keys with an incorrect deviceId", function(done) {
-        let bobDeviceKeys = {
+        const bobDeviceKeys = {
             algorithms: ['m.olm.v1.curve25519-aes-sha2', 'm.megolm.v1.aes-sha2'],
             device_id: 'bad_device',
             keys: {
@@ -608,10 +608,10 @@ describe("MatrixClient crypto", function() {
             },
         };
 
-        let bobKeys = {};
+        const bobKeys = {};
         bobKeys[bobDeviceId] = bobDeviceKeys;
         aliHttpBackend.when("POST", "/keys/query").respond(200, function(path, content) {
-            let result = {};
+            const result = {};
             result[bobUserId] = bobKeys;
             return {device_keys: result};
         });
@@ -661,8 +661,8 @@ describe("MatrixClient crypto", function() {
             .then(aliSendsFirstMessage)
             .then(bobStartClient)
             .then(function() {
-                let message = aliMessages.shift();
-                let syncData = {
+                const message = aliMessages.shift();
+                const syncData = {
                     next_batch: "x",
                     rooms: {
                         join: {
@@ -684,8 +684,8 @@ describe("MatrixClient crypto", function() {
                 };
                 bobHttpBackend.when("GET", "/sync").respond(200, syncData);
 
-                let deferred = q.defer();
-                let onEvent = function(event) {
+                const deferred = q.defer();
+                const onEvent = function(event) {
                     console.log(bobClient.credentials.userId + " received event",
                                 event);
 
@@ -718,8 +718,8 @@ describe("MatrixClient crypto", function() {
             .then(aliDownloadsKeys)
             .then(function() {
                 aliClient.setDeviceBlocked(bobUserId, bobDeviceId, true);
-                let p1 = sendMessage(aliClient);
-                let p2 = expectAliQueryKeys()
+                const p1 = sendMessage(aliClient);
+                const p2 = expectAliQueryKeys()
                     .then(expectAliClaimKeys)
                     .then(function() {
                         return expectSendMessageRequest(aliHttpBackend);
@@ -765,7 +765,7 @@ describe("MatrixClient crypto", function() {
             .then(bobUploadsKeys)
             .then(aliStartClient)
             .then(function() {
-                let syncData = {
+                const syncData = {
                     next_batch: '2',
                     to_device: {
                         events: [
diff --git a/spec/integ/matrix-client-event-emitter.spec.js b/spec/integ/matrix-client-event-emitter.spec.js
index 24741c29a..26bf8bcf3 100644
--- a/spec/integ/matrix-client-event-emitter.spec.js
+++ b/spec/integ/matrix-client-event-emitter.spec.js
@@ -1,14 +1,14 @@
 "use strict";
-let sdk = require("../..");
-let HttpBackend = require("../mock-request");
-let utils = require("../test-utils");
+const sdk = require("../..");
+const HttpBackend = require("../mock-request");
+const utils = require("../test-utils");
 
 describe("MatrixClient events", function() {
-    let baseUrl = "http://localhost.or.something";
+    const baseUrl = "http://localhost.or.something";
     let client;
     let httpBackend;
-    let selfUserId = "@alice:localhost";
-    let selfAccessToken = "aseukfgwef";
+    const selfUserId = "@alice:localhost";
+    const selfAccessToken = "aseukfgwef";
 
     beforeEach(function() {
         utils.beforeEach(this); // eslint-disable-line no-invalid-this
@@ -29,7 +29,7 @@ describe("MatrixClient events", function() {
     });
 
     describe("emissions", function() {
-        let SYNC_DATA = {
+        const SYNC_DATA = {
             next_batch: "s_5_3",
             presence: {
                 events: [
@@ -67,7 +67,7 @@ describe("MatrixClient events", function() {
                 },
             },
         };
-        let NEXT_SYNC_DATA = {
+        const NEXT_SYNC_DATA = {
             next_batch: "e_6_7",
             rooms: {
                 join: {
@@ -198,7 +198,7 @@ describe("MatrixClient events", function() {
             httpBackend.when("GET", "/sync").respond(200, SYNC_DATA);
             httpBackend.when("GET", "/sync").respond(200, NEXT_SYNC_DATA);
 
-            let roomStateEventTypes = [
+            const roomStateEventTypes = [
                 "m.room.member", "m.room.create",
             ];
             let eventsInvokeCount = 0;
@@ -206,7 +206,7 @@ describe("MatrixClient events", function() {
             let newMemberInvokeCount = 0;
             client.on("RoomState.events", function(event, state) {
                 eventsInvokeCount++;
-                let index = roomStateEventTypes.indexOf(event.getType());
+                const index = roomStateEventTypes.indexOf(event.getType());
                 expect(index).not.toEqual(
                     -1, "Unexpected room state event type: " + event.getType()
                 );
diff --git a/spec/integ/matrix-client-event-timeline.spec.js b/spec/integ/matrix-client-event-timeline.spec.js
index e53b82495..1acc1318c 100644
--- a/spec/integ/matrix-client-event-timeline.spec.js
+++ b/spec/integ/matrix-client-event-timeline.spec.js
@@ -1,29 +1,29 @@
 "use strict";
-let q = require("q");
-let sdk = require("../..");
-let HttpBackend = require("../mock-request");
-let utils = require("../test-utils");
-let EventTimeline = sdk.EventTimeline;
+const q = require("q");
+const sdk = require("../..");
+const HttpBackend = require("../mock-request");
+const utils = require("../test-utils");
+const EventTimeline = sdk.EventTimeline;
 
-let baseUrl = "http://localhost.or.something";
-let userId = "@alice:localhost";
-let userName = "Alice";
-let accessToken = "aseukfgwef";
-let roomId = "!foo:bar";
-let otherUserId = "@bob:localhost";
+const baseUrl = "http://localhost.or.something";
+const userId = "@alice:localhost";
+const userName = "Alice";
+const accessToken = "aseukfgwef";
+const roomId = "!foo:bar";
+const otherUserId = "@bob:localhost";
 
-let USER_MEMBERSHIP_EVENT = utils.mkMembership({
+const USER_MEMBERSHIP_EVENT = utils.mkMembership({
     room: roomId, mship: "join", user: userId, name: userName,
 });
 
-let ROOM_NAME_EVENT = utils.mkEvent({
+const ROOM_NAME_EVENT = utils.mkEvent({
     type: "m.room.name", room: roomId, user: otherUserId,
     content: {
         name: "Old room name",
     },
 });
 
-let INITIAL_SYNC_DATA = {
+const INITIAL_SYNC_DATA = {
     next_batch: "s_5_3",
     rooms: {
         join: {
@@ -57,7 +57,7 @@ let INITIAL_SYNC_DATA = {
     },
 };
 
-let EVENTS = [
+const EVENTS = [
     utils.mkMessage({
         room: roomId, user: userId, msg: "we",
     }),
@@ -81,7 +81,7 @@ function startClient(httpBackend, client) {
     client.startClient();
 
     // set up a promise which will resolve once the client is initialised
-    let deferred = q.defer();
+    const deferred = q.defer();
     client.on("sync", function(state) {
         console.log("sync", state);
         if (state != "SYNCING") {
@@ -120,8 +120,8 @@ describe("getEventTimeline support", function() {
 
         startClient(httpBackend, client
         ).then(function() {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
             expect(function() {
                 client.getEventTimeline(timelineSet, "event");
             }).toThrow();
@@ -138,8 +138,8 @@ describe("getEventTimeline support", function() {
 
         startClient(httpBackend, client
         ).then(function() {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
             expect(function() {
                 client.getEventTimeline(timelineSet, "event");
             }).not.toThrow();
@@ -246,8 +246,8 @@ describe("MatrixClient event timelines", function() {
 
     describe("getEventTimeline", function() {
         it("should create a new timeline for new events", function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
             httpBackend.when("GET", "/rooms/!foo%3Abar/context/event1%3Abar")
                 .respond(200, function() {
                     return {
@@ -279,8 +279,8 @@ describe("MatrixClient event timelines", function() {
         });
 
         it("should return existing timeline for known events", function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
             httpBackend.when("GET", "/sync").respond(200, {
                 next_batch: "s_5_4",
                 rooms: {
@@ -311,8 +311,8 @@ describe("MatrixClient event timelines", function() {
         });
 
         it("should update timelines where they overlap a previous /sync", function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
             httpBackend.when("GET", "/sync").respond(200, {
                 next_batch: "s_5_4",
                 rooms: {
@@ -361,8 +361,8 @@ describe("MatrixClient event timelines", function() {
 
         it("should join timelines where they overlap a previous /context",
           function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
 
             // we fetch event 0, then 2, then 3, and finally 1. 1 is returned
             // with context which joins them all up.
@@ -455,8 +455,8 @@ describe("MatrixClient event timelines", function() {
         });
 
         it("should fail gracefully if there is no event field", function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
             // we fetch event 0, then 2, then 3, and finally 1. 1 is returned
             // with context which joins them all up.
             httpBackend.when("GET", "/rooms/!foo%3Abar/context/event1")
@@ -484,8 +484,8 @@ describe("MatrixClient event timelines", function() {
 
     describe("paginateEventTimeline", function() {
         it("should allow you to paginate backwards", function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
 
             httpBackend.when("GET", "/rooms/!foo%3Abar/context/" +
                              encodeURIComponent(EVENTS[0].event_id))
@@ -502,7 +502,7 @@ describe("MatrixClient event timelines", function() {
 
             httpBackend.when("GET", "/rooms/!foo%3Abar/messages")
                 .check(function(req) {
-                    let params = req.queryParams;
+                    const params = req.queryParams;
                     expect(params.dir).toEqual("b");
                     expect(params.from).toEqual("start_token0");
                     expect(params.limit).toEqual(30);
@@ -535,8 +535,8 @@ describe("MatrixClient event timelines", function() {
 
 
         it("should allow you to paginate forwards", function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
 
             httpBackend.when("GET", "/rooms/!foo%3Abar/context/" +
                              encodeURIComponent(EVENTS[0].event_id))
@@ -553,7 +553,7 @@ describe("MatrixClient event timelines", function() {
 
             httpBackend.when("GET", "/rooms/!foo%3Abar/messages")
                 .check(function(req) {
-                    let params = req.queryParams;
+                    const params = req.queryParams;
                     expect(params.dir).toEqual("f");
                     expect(params.from).toEqual("end_token0");
                     expect(params.limit).toEqual(20);
@@ -587,8 +587,8 @@ describe("MatrixClient event timelines", function() {
     });
 
     describe("event timeline for sent events", function() {
-        let TXN_ID = "txn1";
-        let event = utils.mkMessage({
+        const TXN_ID = "txn1";
+        const event = utils.mkMessage({
             room: roomId, user: userId, msg: "a body",
         });
         event.unsigned = {transaction_id: TXN_ID};
@@ -618,8 +618,8 @@ describe("MatrixClient event timelines", function() {
         });
 
         it("should work when /send returns before /sync", function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
 
             client.sendTextMessage(roomId, "a body", TXN_ID).then(function(res) {
                 expect(res.event_id).toEqual(event.event_id);
@@ -642,8 +642,8 @@ describe("MatrixClient event timelines", function() {
         });
 
         it("should work when /send returns after /sync", function(done) {
-            let room = client.getRoom(roomId);
-            let timelineSet = room.getTimelineSets()[0];
+            const room = client.getRoom(roomId);
+            const timelineSet = room.getTimelineSets()[0];
 
             // initiate the send, and set up checks to be done when it completes
             // - but note that it won't complete until after the /sync does, below.
@@ -675,10 +675,10 @@ describe("MatrixClient event timelines", function() {
         // https://github.com/vector-im/vector-web/issues/1389
 
         // a state event, followed by a redaction thereof
-        let event = utils.mkMembership({
+        const event = utils.mkMembership({
             room: roomId, mship: "join", user: otherUserId,
         });
-        let redaction = utils.mkEvent({
+        const redaction = utils.mkEvent({
             type: "m.room.redaction",
             room_id: roomId,
             sender: otherUserId,
@@ -686,7 +686,7 @@ describe("MatrixClient event timelines", function() {
         });
         redaction.redacts = event.event_id;
 
-        let syncData = {
+        const syncData = {
             next_batch: "batch1",
             rooms: {
                 join: {},
@@ -704,12 +704,12 @@ describe("MatrixClient event timelines", function() {
         httpBackend.when("GET", "/sync").respond(200, syncData);
 
         httpBackend.flush().then(function() {
-            let room = client.getRoom(roomId);
-            let tl = room.getLiveTimeline();
+            const room = client.getRoom(roomId);
+            const tl = room.getLiveTimeline();
             expect(tl.getEvents().length).toEqual(3);
             expect(tl.getEvents()[1].isRedacted()).toBe(true);
 
-            let sync2 = {
+            const sync2 = {
                 next_batch: "batch2",
                 rooms: {
                     join: {},
@@ -730,8 +730,8 @@ describe("MatrixClient event timelines", function() {
 
             return httpBackend.flush();
         }).then(function() {
-            let room = client.getRoom(roomId);
-            let tl = room.getLiveTimeline();
+            const room = client.getRoom(roomId);
+            const tl = room.getLiveTimeline();
             expect(tl.getEvents().length).toEqual(1);
         }).catch(utils.failTest).done(done);
     });
diff --git a/spec/integ/matrix-client-methods.spec.js b/spec/integ/matrix-client-methods.spec.js
index 5affcf936..662d9211c 100644
--- a/spec/integ/matrix-client-methods.spec.js
+++ b/spec/integ/matrix-client-methods.spec.js
@@ -1,28 +1,28 @@
 "use strict";
-let sdk = require("../..");
-let HttpBackend = require("../mock-request");
-let publicGlobals = require("../../lib/matrix");
-let Room = publicGlobals.Room;
-let MatrixInMemoryStore = publicGlobals.MatrixInMemoryStore;
-let Filter = publicGlobals.Filter;
-let utils = require("../test-utils");
-let MockStorageApi = require("../MockStorageApi");
+const sdk = require("../..");
+const HttpBackend = require("../mock-request");
+const publicGlobals = require("../../lib/matrix");
+const Room = publicGlobals.Room;
+const MatrixInMemoryStore = publicGlobals.MatrixInMemoryStore;
+const Filter = publicGlobals.Filter;
+const utils = require("../test-utils");
+const MockStorageApi = require("../MockStorageApi");
 
 describe("MatrixClient", function() {
-    let baseUrl = "http://localhost.or.something";
+    const baseUrl = "http://localhost.or.something";
     let client = null;
     let httpBackend = null;
     let store = null;
     let sessionStore = null;
-    let userId = "@alice:localhost";
-    let accessToken = "aseukfgwef";
+    const userId = "@alice:localhost";
+    const accessToken = "aseukfgwef";
 
     beforeEach(function() {
         utils.beforeEach(this); // eslint-disable-line no-invalid-this
         httpBackend = new HttpBackend();
         store = new MatrixInMemoryStore();
 
-        let mockStorage = new MockStorageApi();
+        const mockStorage = new MockStorageApi();
         sessionStore = new sdk.WebStorageSessionStore(mockStorage);
 
         sdk.request(httpBackend.requestFn);
@@ -41,7 +41,7 @@ describe("MatrixClient", function() {
     });
 
     describe("uploadContent", function() {
-        let buf = new Buffer('hello world');
+        const buf = new Buffer('hello world');
         it("should upload the file", function(done) {
             httpBackend.when(
                 "POST", "/_matrix/media/v1/upload"
@@ -54,7 +54,7 @@ describe("MatrixClient", function() {
                 expect(req.opts.timeout).toBe(undefined);
             }).respond(200, "content");
 
-            let prom = client.uploadContent({
+            const prom = client.uploadContent({
                 stream: buf,
                 name: "hi.txt",
                 type: "text/plain",
@@ -62,7 +62,7 @@ describe("MatrixClient", function() {
 
             expect(prom).toBeDefined();
 
-            let uploads = client.getCurrentUploads();
+            const uploads = client.getCurrentUploads();
             expect(uploads.length).toEqual(1);
             expect(uploads[0].promise).toBe(prom);
             expect(uploads[0].loaded).toEqual(0);
@@ -71,7 +71,7 @@ describe("MatrixClient", function() {
                 // for backwards compatibility, we return the raw JSON
                 expect(response).toEqual("content");
 
-                let uploads = client.getCurrentUploads();
+                const uploads = client.getCurrentUploads();
                 expect(uploads.length).toEqual(0);
             }).catch(utils.failTest).done(done);
 
@@ -126,13 +126,13 @@ describe("MatrixClient", function() {
         });
 
         it("should return a promise which can be cancelled", function(done) {
-            let prom = client.uploadContent({
+            const prom = client.uploadContent({
                 stream: buf,
                 name: "hi.txt",
                 type: "text/plain",
             });
 
-            let uploads = client.getCurrentUploads();
+            const uploads = client.getCurrentUploads();
             expect(uploads.length).toEqual(1);
             expect(uploads[0].promise).toBe(prom);
             expect(uploads[0].loaded).toEqual(0);
@@ -142,19 +142,19 @@ describe("MatrixClient", function() {
             }, function(error) {
                 expect(error).toEqual("aborted");
 
-                let uploads = client.getCurrentUploads();
+                const uploads = client.getCurrentUploads();
                 expect(uploads.length).toEqual(0);
             }).catch(utils.failTest).done(done);
 
-            let r = client.cancelUpload(prom);
+            const r = client.cancelUpload(prom);
             expect(r).toBe(true);
         });
     });
 
     describe("joinRoom", function() {
         it("should no-op if you've already joined a room", function() {
-            let roomId = "!foo:bar";
-            let room = new Room(roomId);
+            const roomId = "!foo:bar";
+            const room = new Room(roomId);
             room.addLiveEvents([
                 utils.mkMembership({
                     user: userId, room: roomId, mship: "join", event: true,
@@ -167,10 +167,10 @@ describe("MatrixClient", function() {
     });
 
     describe("getFilter", function() {
-        let filterId = "f1lt3r1d";
+        const filterId = "f1lt3r1d";
 
         it("should return a filter from the store if allowCached", function(done) {
-            let filter = Filter.fromJson(userId, filterId, {
+            const filter = Filter.fromJson(userId, filterId, {
                 event_format: "client",
             });
             store.storeFilter(filter);
@@ -183,7 +183,7 @@ describe("MatrixClient", function() {
 
         it("should do an HTTP request if !allowCached even if one exists",
         function(done) {
-            let httpFilterDefinition = {
+            const httpFilterDefinition = {
                 event_format: "federation",
             };
 
@@ -191,7 +191,7 @@ describe("MatrixClient", function() {
                 "GET", "/user/" + encodeURIComponent(userId) + "/filter/" + filterId
             ).respond(200, httpFilterDefinition);
 
-            let storeFilter = Filter.fromJson(userId, filterId, {
+            const storeFilter = Filter.fromJson(userId, filterId, {
                 event_format: "client",
             });
             store.storeFilter(storeFilter);
@@ -205,7 +205,7 @@ describe("MatrixClient", function() {
 
         it("should do an HTTP request if nothing is in the cache and then store it",
         function(done) {
-            let httpFilterDefinition = {
+            const httpFilterDefinition = {
                 event_format: "federation",
             };
             expect(store.getFilter(userId, filterId)).toBeNull();
@@ -224,12 +224,12 @@ describe("MatrixClient", function() {
     });
 
     describe("createFilter", function() {
-        let filterId = "f1llllllerid";
+        const filterId = "f1llllllerid";
 
         it("should do an HTTP request and then store the filter", function(done) {
             expect(store.getFilter(userId, filterId)).toBeNull();
 
-            let filterDefinition = {
+            const filterDefinition = {
                 event_format: "client",
             };
 
@@ -252,7 +252,7 @@ describe("MatrixClient", function() {
     });
 
     describe("searching", function() {
-        let response = {
+        const response = {
             search_categories: {
                 room_events: {
                     count: 24,
@@ -297,9 +297,9 @@ describe("MatrixClient", function() {
 
     describe("downloadKeys", function() {
         it("should do an HTTP request and then store the keys", function(done) {
-            let ed25519key = "7wG2lzAqbjcyEkOP7O4gU7ItYcn+chKzh5sT/5r2l78";
+            const ed25519key = "7wG2lzAqbjcyEkOP7O4gU7ItYcn+chKzh5sT/5r2l78";
             // ed25519key = client.getDeviceEd25519Key();
-            let borisKeys = {
+            const borisKeys = {
                 dev1: {
                     algorithms: ["1"],
                     device_id: "dev1",
@@ -315,7 +315,7 @@ describe("MatrixClient", function() {
                     user_id: "boris",
                 },
             };
-            let chazKeys = {
+            const chazKeys = {
                 dev2: {
                     algorithms: ["2"],
                     device_id: "dev2",
@@ -376,7 +376,7 @@ describe("MatrixClient", function() {
     });
 
     describe("deleteDevice", function() {
-        let auth = {a: 1};
+        const auth = {a: 1};
         it("should pass through an auth dict", function(done) {
             httpBackend.when(
                 "DELETE", "/_matrix/client/unstable/devices/my_device"
@@ -394,7 +394,7 @@ describe("MatrixClient", function() {
 });
 
 function assertObjectContains(obj, expected) {
-    for (let k in expected) {
+    for (const k in expected) {
         if (expected.hasOwnProperty(k)) {
             expect(obj[k]).toEqual(expected[k]);
         }
diff --git a/spec/integ/matrix-client-opts.spec.js b/spec/integ/matrix-client-opts.spec.js
index 688a52645..d339d9ae8 100644
--- a/spec/integ/matrix-client-opts.spec.js
+++ b/spec/integ/matrix-client-opts.spec.js
@@ -1,18 +1,18 @@
 "use strict";
-let sdk = require("../..");
-let MatrixClient = sdk.MatrixClient;
-let HttpBackend = require("../mock-request");
-let utils = require("../test-utils");
+const sdk = require("../..");
+const MatrixClient = sdk.MatrixClient;
+const HttpBackend = require("../mock-request");
+const utils = require("../test-utils");
 
 describe("MatrixClient opts", function() {
-    let baseUrl = "http://localhost.or.something";
+    const baseUrl = "http://localhost.or.something";
     let client = null;
     let httpBackend = null;
-    let userId = "@alice:localhost";
-    let userB = "@bob:localhost";
-    let accessToken = "aseukfgwef";
-    let roomId = "!foo:bar";
-    let syncData = {
+    const userId = "@alice:localhost";
+    const userB = "@bob:localhost";
+    const accessToken = "aseukfgwef";
+    const roomId = "!foo:bar";
+    const syncData = {
         next_batch: "s_5_3",
         presence: {},
         rooms: {
@@ -79,7 +79,7 @@ describe("MatrixClient opts", function() {
         });
 
         it("should be able to send messages", function(done) {
-            let eventId = "$flibble:wibble";
+            const eventId = "$flibble:wibble";
             httpBackend.when("PUT", "/txn1").respond(200, {
                 event_id: eventId,
             });
@@ -91,7 +91,7 @@ describe("MatrixClient opts", function() {
         });
 
         it("should be able to sync / get new events", function(done) {
-            let expectedEventTypes = [ // from /initialSync
+            const expectedEventTypes = [ // from /initialSync
                 "m.room.message", "m.room.name", "m.room.member", "m.room.member",
                 "m.room.create",
             ];
diff --git a/spec/integ/matrix-client-retrying.spec.js b/spec/integ/matrix-client-retrying.spec.js
index 3fdcb2451..f96660122 100644
--- a/spec/integ/matrix-client-retrying.spec.js
+++ b/spec/integ/matrix-client-retrying.spec.js
@@ -1,17 +1,17 @@
 "use strict";
-let sdk = require("../..");
-let HttpBackend = require("../mock-request");
-let utils = require("../test-utils");
-let EventStatus = sdk.EventStatus;
+const sdk = require("../..");
+const HttpBackend = require("../mock-request");
+const utils = require("../test-utils");
+const EventStatus = sdk.EventStatus;
 
 describe("MatrixClient retrying", function() {
-    let baseUrl = "http://localhost.or.something";
+    const baseUrl = "http://localhost.or.something";
     let client = null;
     let httpBackend = null;
     let scheduler;
-    let userId = "@alice:localhost";
-    let accessToken = "aseukfgwef";
-    let roomId = "!room:here";
+    const userId = "@alice:localhost";
+    const accessToken = "aseukfgwef";
+    const roomId = "!room:here";
     let room;
 
     beforeEach(function() {
@@ -61,7 +61,7 @@ describe("MatrixClient retrying", function() {
         });
 
         // both events should be in the timeline at this point
-        let tl = room.getLiveTimeline().getEvents();
+        const tl = room.getLiveTimeline().getEvents();
         expect(tl.length).toEqual(2);
         ev1 = tl[0];
         ev2 = tl[1];
diff --git a/spec/integ/matrix-client-room-timeline.spec.js b/spec/integ/matrix-client-room-timeline.spec.js
index dbd35f8e8..ac9a91ba1 100644
--- a/spec/integ/matrix-client-room-timeline.spec.js
+++ b/spec/integ/matrix-client-room-timeline.spec.js
@@ -1,29 +1,29 @@
 "use strict";
-let sdk = require("../..");
-let EventStatus = sdk.EventStatus;
-let HttpBackend = require("../mock-request");
-let utils = require("../test-utils");
+const sdk = require("../..");
+const EventStatus = sdk.EventStatus;
+const HttpBackend = require("../mock-request");
+const utils = require("../test-utils");
 
 describe("MatrixClient room timelines", function() {
-    let baseUrl = "http://localhost.or.something";
+    const baseUrl = "http://localhost.or.something";
     let client = null;
     let httpBackend = null;
-    let userId = "@alice:localhost";
-    let userName = "Alice";
-    let accessToken = "aseukfgwef";
-    let roomId = "!foo:bar";
-    let otherUserId = "@bob:localhost";
-    let USER_MEMBERSHIP_EVENT = utils.mkMembership({
+    const userId = "@alice:localhost";
+    const userName = "Alice";
+    const accessToken = "aseukfgwef";
+    const roomId = "!foo:bar";
+    const otherUserId = "@bob:localhost";
+    const USER_MEMBERSHIP_EVENT = utils.mkMembership({
         room: roomId, mship: "join", user: userId, name: userName,
     });
-    let ROOM_NAME_EVENT = utils.mkEvent({
+    const ROOM_NAME_EVENT = utils.mkEvent({
         type: "m.room.name", room: roomId, user: otherUserId,
         content: {
             name: "Old room name",
         },
     });
     let NEXT_SYNC_DATA;
-    let SYNC_DATA = {
+    const SYNC_DATA = {
         next_batch: "s_5_3",
         rooms: {
             join: {
@@ -135,7 +135,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 expect(room.timeline.length).toEqual(1);
 
                 client.sendTextMessage(roomId, "I am a fish", "txn1");
@@ -144,7 +144,7 @@ describe("MatrixClient room timelines", function() {
                 // check status
                 expect(room.timeline[1].status).toEqual(EventStatus.SENDING);
                 // check member
-                let member = room.timeline[1].sender;
+                const member = room.timeline[1].sender;
                 expect(member.userId).toEqual(userId);
                 expect(member.name).toEqual(userName);
 
@@ -157,12 +157,12 @@ describe("MatrixClient room timelines", function() {
 
         it("should be updated correctly when the send request finishes " +
         "BEFORE the event comes down the event stream", function(done) {
-            let eventId = "$foo:bar";
+            const eventId = "$foo:bar";
             httpBackend.when("PUT", "/txn1").respond(200, {
                 event_id: eventId,
             });
 
-            let ev = utils.mkMessage({
+            const ev = utils.mkMessage({
                 body: "I am a fish", user: userId, room: roomId,
             });
             ev.event_id = eventId;
@@ -173,7 +173,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 client.sendTextMessage(roomId, "I am a fish", "txn1").done(
                 function() {
                     expect(room.timeline[1].getId()).toEqual(eventId);
@@ -189,12 +189,12 @@ describe("MatrixClient room timelines", function() {
 
         it("should be updated correctly when the send request finishes " +
         "AFTER the event comes down the event stream", function(done) {
-            let eventId = "$foo:bar";
+            const eventId = "$foo:bar";
             httpBackend.when("PUT", "/txn1").respond(200, {
                 event_id: eventId,
             });
 
-            let ev = utils.mkMessage({
+            const ev = utils.mkMessage({
                 body: "I am a fish", user: userId, room: roomId,
             });
             ev.event_id = eventId;
@@ -205,8 +205,8 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
-                let promise = client.sendTextMessage(roomId, "I am a fish", "txn1");
+                const room = client.getRoom(roomId);
+                const promise = client.sendTextMessage(roomId, "I am a fish", "txn1");
                 httpBackend.flush("/sync", 1).done(function() {
                     expect(room.timeline.length).toEqual(2);
                     httpBackend.flush("/txn1", 1);
@@ -223,7 +223,7 @@ describe("MatrixClient room timelines", function() {
 
     describe("paginated events", function() {
         let sbEvents;
-        let sbEndTok = "pagin_end";
+        const sbEndTok = "pagin_end";
 
         beforeEach(function() {
             sbEvents = [];
@@ -242,7 +242,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 expect(room.timeline.length).toEqual(1);
 
                 client.scrollback(room).done(function() {
@@ -268,14 +268,14 @@ describe("MatrixClient room timelines", function() {
             // <Bob> hello
 
             // make an m.room.member event for alice's join
-            let joinMshipEvent = utils.mkMembership({
+            const joinMshipEvent = utils.mkMembership({
                 mship: "join", user: userId, room: roomId, name: "Old Alice",
                 url: null,
             });
 
             // make an m.room.member event with prev_content for alice's nick
             // change
-            let oldMshipEvent = utils.mkMembership({
+            const oldMshipEvent = utils.mkMembership({
                 mship: "join", user: userId, room: roomId, name: userName,
                 url: "mxc://some/url",
             });
@@ -302,17 +302,17 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 // sync response
                 expect(room.timeline.length).toEqual(1);
 
                 client.scrollback(room).done(function() {
                     expect(room.timeline.length).toEqual(5);
-                    let joinMsg = room.timeline[0];
+                    const joinMsg = room.timeline[0];
                     expect(joinMsg.sender.name).toEqual("Old Alice");
-                    let oldMsg = room.timeline[1];
+                    const oldMsg = room.timeline[1];
                     expect(oldMsg.sender.name).toEqual("Old Alice");
-                    let newMsg = room.timeline[3];
+                    const newMsg = room.timeline[3];
                     expect(newMsg.sender.name).toEqual(userName);
                     done();
                 });
@@ -338,7 +338,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 expect(room.timeline.length).toEqual(1);
 
                 client.scrollback(room).done(function() {
@@ -366,7 +366,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 expect(room.oldState.paginationToken).toBeDefined();
 
                 client.scrollback(room, 1).done(function() {
@@ -384,7 +384,7 @@ describe("MatrixClient room timelines", function() {
 
     describe("new events", function() {
         it("should be added to the right place in the timeline", function(done) {
-            let eventData = [
+            const eventData = [
                 utils.mkMessage({user: userId, room: roomId}),
                 utils.mkMessage({user: userId, room: roomId}),
             ];
@@ -394,7 +394,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
 
                 let index = 0;
                 client.on("Room.timeline", function(event, rm, toStart) {
@@ -420,7 +420,7 @@ describe("MatrixClient room timelines", function() {
         });
 
         it("should set the right event.sender values", function(done) {
-            let eventData = [
+            const eventData = [
                 utils.mkMessage({user: userId, room: roomId}),
                 utils.mkMembership({
                     user: userId, room: roomId, mship: "join", name: "New Name",
@@ -434,10 +434,10 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 httpBackend.flush("/sync", 1).then(function() {
-                    let preNameEvent = room.timeline[room.timeline.length - 3];
-                    let postNameEvent = room.timeline[room.timeline.length - 1];
+                    const preNameEvent = room.timeline[room.timeline.length - 3];
+                    const postNameEvent = room.timeline[room.timeline.length - 1];
                     expect(preNameEvent.sender.name).toEqual(userName);
                     expect(postNameEvent.sender.name).toEqual("New Name");
                 }).catch(utils.failTest).done(done);
@@ -446,7 +446,7 @@ describe("MatrixClient room timelines", function() {
         });
 
         it("should set the right room.name", function(done) {
-            let secondRoomNameEvent = utils.mkEvent({
+            const secondRoomNameEvent = utils.mkEvent({
                 user: userId, room: roomId, type: "m.room.name", content: {
                     name: "Room 2",
                 },
@@ -458,7 +458,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 let nameEmitCount = 0;
                 client.on("Room.name", function(rm) {
                     nameEmitCount += 1;
@@ -468,7 +468,7 @@ describe("MatrixClient room timelines", function() {
                     expect(nameEmitCount).toEqual(1);
                     expect(room.name).toEqual("Room 2");
                     // do another round
-                    let thirdRoomNameEvent = utils.mkEvent({
+                    const thirdRoomNameEvent = utils.mkEvent({
                         user: userId, room: roomId, type: "m.room.name", content: {
                             name: "Room 3",
                         },
@@ -487,9 +487,9 @@ describe("MatrixClient room timelines", function() {
         });
 
         it("should set the right room members", function(done) {
-            let userC = "@cee:bar";
-            let userD = "@dee:bar";
-            let eventData = [
+            const userC = "@cee:bar";
+            const userD = "@dee:bar";
+            const eventData = [
                 utils.mkMembership({
                     user: userC, room: roomId, mship: "join", name: "C",
                 }),
@@ -505,7 +505,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
                 httpBackend.flush("/sync", 1).then(function() {
                     expect(room.currentState.getMembers().length).toEqual(4);
                     expect(room.currentState.getMember(userC).name).toEqual("C");
@@ -524,7 +524,7 @@ describe("MatrixClient room timelines", function() {
 
     describe("gappy sync", function() {
         it("should copy the last known state to the new timeline", function(done) {
-            let eventData = [
+            const eventData = [
                 utils.mkMessage({user: userId, room: roomId}),
             ];
             setNextSyncData(eventData);
@@ -534,7 +534,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
 
                 httpBackend.flush("/messages", 1);
                 httpBackend.flush("/sync", 1).done(function() {
@@ -556,7 +556,7 @@ describe("MatrixClient room timelines", function() {
         });
 
         it("should emit a 'Room.timelineReset' event", function(done) {
-            let eventData = [
+            const eventData = [
                 utils.mkMessage({user: userId, room: roomId}),
             ];
             setNextSyncData(eventData);
@@ -566,7 +566,7 @@ describe("MatrixClient room timelines", function() {
                 if (state !== "PREPARED") {
                     return;
                 }
-                let room = client.getRoom(roomId);
+                const room = client.getRoom(roomId);
 
                 let emitCount = 0;
                 client.on("Room.timelineReset", function(emitRoom) {
diff --git a/spec/integ/matrix-client-syncing.spec.js b/spec/integ/matrix-client-syncing.spec.js
index d4414fb6f..8a8c8a721 100644
--- a/spec/integ/matrix-client-syncing.spec.js
+++ b/spec/integ/matrix-client-syncing.spec.js
@@ -1,22 +1,22 @@
 "use strict";
-let sdk = require("../..");
-let HttpBackend = require("../mock-request");
-let utils = require("../test-utils");
-let MatrixEvent = sdk.MatrixEvent;
-let EventTimeline = sdk.EventTimeline;
+const sdk = require("../..");
+const HttpBackend = require("../mock-request");
+const utils = require("../test-utils");
+const MatrixEvent = sdk.MatrixEvent;
+const EventTimeline = sdk.EventTimeline;
 
 describe("MatrixClient syncing", function() {
-    let baseUrl = "http://localhost.or.something";
+    const baseUrl = "http://localhost.or.something";
     let client = null;
     let httpBackend = null;
-    let selfUserId = "@alice:localhost";
-    let selfAccessToken = "aseukfgwef";
-    let otherUserId = "@bob:localhost";
-    let userA = "@alice:bar";
-    let userB = "@bob:bar";
-    let userC = "@claire:bar";
-    let roomOne = "!foo:localhost";
-    let roomTwo = "!bar:localhost";
+    const selfUserId = "@alice:localhost";
+    const selfAccessToken = "aseukfgwef";
+    const otherUserId = "@bob:localhost";
+    const userA = "@alice:bar";
+    const userB = "@bob:bar";
+    const userC = "@claire:bar";
+    const roomOne = "!foo:localhost";
+    const roomTwo = "!bar:localhost";
 
     beforeEach(function() {
         utils.beforeEach(this); // eslint-disable-line no-invalid-this
@@ -37,7 +37,7 @@ describe("MatrixClient syncing", function() {
     });
 
     describe("startClient", function() {
-        let syncData = {
+        const syncData = {
             next_batch: "batch_token",
             rooms: {},
             presence: {},
@@ -69,7 +69,7 @@ describe("MatrixClient syncing", function() {
     });
 
     describe("resolving invites to profile info", function() {
-        let syncData = {
+        const syncData = {
             next_batch: "s_5_3",
             presence: {
                 events: [],
@@ -130,7 +130,7 @@ describe("MatrixClient syncing", function() {
             });
 
             httpBackend.flush().done(function() {
-                let member = client.getRoom(roomOne).getMember(userC);
+                const member = client.getRoom(roomOne).getMember(userC);
                 expect(member.name).toEqual("The Boss");
                 expect(
                     member.getAvatarUrl("home.server.url", null, null, null, false)
@@ -158,7 +158,7 @@ describe("MatrixClient syncing", function() {
             });
 
             httpBackend.flush().done(function() {
-                let member = client.getRoom(roomOne).getMember(userC);
+                const member = client.getRoom(roomOne).getMember(userC);
                 expect(member.name).toEqual("The Ghost");
                 done();
             });
@@ -207,7 +207,7 @@ describe("MatrixClient syncing", function() {
             client.startClient();
 
             httpBackend.flush().done(function() {
-                let member = client.getRoom(roomOne).getMember(userC);
+                const member = client.getRoom(roomOne).getMember(userC);
                 expect(member.name).toEqual(userC);
                 expect(
                     member.getAvatarUrl("home.server.url", null, null, null, false)
@@ -218,7 +218,7 @@ describe("MatrixClient syncing", function() {
     });
 
     describe("users", function() {
-        let syncData = {
+        const syncData = {
             next_batch: "nb",
             presence: {
                 events: [
@@ -247,10 +247,10 @@ describe("MatrixClient syncing", function() {
     });
 
     describe("room state", function() {
-        let msgText = "some text here";
-        let otherDisplayName = "Bob Smith";
+        const msgText = "some text here";
+        const otherDisplayName = "Bob Smith";
 
-        let syncData = {
+        const syncData = {
             rooms: {
                 join: {
 
@@ -315,7 +315,7 @@ describe("MatrixClient syncing", function() {
             },
         };
 
-        let nextSyncData = {
+        const nextSyncData = {
             rooms: {
                 join: {
 
@@ -359,7 +359,7 @@ describe("MatrixClient syncing", function() {
             client.startClient();
 
             httpBackend.flush().done(function() {
-                let room = client.getRoom(roomOne);
+                const room = client.getRoom(roomOne);
                 // should have clobbered the name to the one from /events
                 expect(room.name).toEqual(
                     nextSyncData.rooms.join[roomOne].state.events[0].content.name
@@ -375,7 +375,7 @@ describe("MatrixClient syncing", function() {
             client.startClient();
 
             httpBackend.flush().done(function() {
-                let room = client.getRoom(roomTwo);
+                const room = client.getRoom(roomTwo);
                 // should have added the message from /events
                 expect(room.timeline.length).toEqual(2);
                 expect(room.timeline[1].getContent().body).toEqual(msgText);
@@ -389,7 +389,7 @@ describe("MatrixClient syncing", function() {
 
             client.startClient();
             httpBackend.flush().done(function() {
-                let room = client.getRoom(roomTwo);
+                const room = client.getRoom(roomTwo);
                 // should use the display name of the other person.
                 expect(room.name).toEqual(otherDisplayName);
                 done();
@@ -403,7 +403,7 @@ describe("MatrixClient syncing", function() {
             client.startClient();
 
             httpBackend.flush().done(function() {
-                let room = client.getRoom(roomTwo);
+                const room = client.getRoom(roomTwo);
                 let member = room.getMember(otherUserId);
                 expect(member).toBeDefined();
                 expect(member.typing).toEqual(true);
@@ -425,7 +425,7 @@ describe("MatrixClient syncing", function() {
 
     describe("timeline", function() {
         beforeEach(function() {
-            let syncData = {
+            const syncData = {
                 next_batch: "batch_token",
                 rooms: {
                     join: {},
@@ -449,7 +449,7 @@ describe("MatrixClient syncing", function() {
         });
 
         it("should set the back-pagination token on new rooms", function(done) {
-            let syncData = {
+            const syncData = {
                 next_batch: "batch_token",
                 rooms: {
                     join: {},
@@ -469,8 +469,8 @@ describe("MatrixClient syncing", function() {
             httpBackend.when("GET", "/sync").respond(200, syncData);
 
             httpBackend.flush().then(function() {
-                let room = client.getRoom(roomTwo);
-                let tok = room.getLiveTimeline()
+                const room = client.getRoom(roomTwo);
+                const tok = room.getLiveTimeline()
                     .getPaginationToken(EventTimeline.BACKWARDS);
                 expect(tok).toEqual("roomtwotok");
                 done();
@@ -478,7 +478,7 @@ describe("MatrixClient syncing", function() {
         });
 
         it("should set the back-pagination token on gappy syncs", function(done) {
-            let syncData = {
+            const syncData = {
                 next_batch: "batch_token",
                 rooms: {
                     join: {},
@@ -502,15 +502,15 @@ describe("MatrixClient syncing", function() {
             client.on("Room.timelineReset", function(room) {
                 resetCallCount++;
 
-                let tl = room.getLiveTimeline();
+                const tl = room.getLiveTimeline();
                 expect(tl.getEvents().length).toEqual(0);
-                let tok = tl.getPaginationToken(EventTimeline.BACKWARDS);
+                const tok = tl.getPaginationToken(EventTimeline.BACKWARDS);
                 expect(tok).toEqual("newerTok");
             });
 
             httpBackend.flush().then(function() {
-                let room = client.getRoom(roomOne);
-                let tl = room.getLiveTimeline();
+                const room = client.getRoom(roomOne);
+                const tl = room.getLiveTimeline();
                 expect(tl.getEvents().length).toEqual(1);
                 expect(resetCallCount).toEqual(1);
                 done();
@@ -519,7 +519,7 @@ describe("MatrixClient syncing", function() {
     });
 
     describe("receipts", function() {
-        let syncData = {
+        const syncData = {
             rooms: {
                 join: {
 
@@ -568,8 +568,8 @@ describe("MatrixClient syncing", function() {
         });
 
         it("should sync receipts from /sync.", function(done) {
-            let ackEvent = syncData.rooms.join[roomOne].timeline.events[0];
-            let receipt = {};
+            const ackEvent = syncData.rooms.join[roomOne].timeline.events[0];
+            const receipt = {};
             receipt[ackEvent.event_id] = {
                 "m.read": {},
             };
@@ -586,7 +586,7 @@ describe("MatrixClient syncing", function() {
             client.startClient();
 
             httpBackend.flush().done(function() {
-                let room = client.getRoom(roomOne);
+                const room = client.getRoom(roomOne);
                 expect(room.getReceiptsForEvent(new MatrixEvent(ackEvent))).toEqual([{
                     type: "m.read",
                     userId: userC,
@@ -647,7 +647,7 @@ describe("MatrixClient syncing", function() {
         });
 
         it("should set the back-pagination token on left rooms", function(done) {
-            let syncData = {
+            const syncData = {
                 next_batch: "batch_token",
                 rooms: {
                     leave: {},
@@ -672,8 +672,8 @@ describe("MatrixClient syncing", function() {
             httpBackend.when("GET", "/sync").respond(200, syncData);
 
             client.syncLeftRooms().then(function() {
-                let room = client.getRoom(roomTwo);
-                let tok = room.getLiveTimeline().getPaginationToken(
+                const room = client.getRoom(roomTwo);
+                const tok = room.getLiveTimeline().getPaginationToken(
                     EventTimeline.BACKWARDS);
 
                 expect(tok).toEqual("pagTok");
diff --git a/spec/integ/megolm.spec.js b/spec/integ/megolm.spec.js
index 1312e12f4..badbff266 100644
--- a/spec/integ/megolm.spec.js
+++ b/spec/integ/megolm.spec.js
@@ -22,15 +22,15 @@ try {
     Olm = require('olm');
 } catch (e) {}
 
-let anotherjson = require('another-json');
-let q = require('q');
+const anotherjson = require('another-json');
+const q = require('q');
 
-let sdk = require('../..');
-let utils = require('../../lib/utils');
-let testUtils = require('../test-utils');
-let MockHttpBackend = require('../mock-request');
+const sdk = require('../..');
+const utils = require('../../lib/utils');
+const testUtils = require('../test-utils');
+const MockHttpBackend = require('../mock-request');
 
-let ROOM_ID = "!room:id";
+const ROOM_ID = "!room:id";
 
 /**
  * Wrapper for a MockStorageApi, MockHttpBackend and MatrixClient
@@ -67,7 +67,7 @@ function TestClient(userId, deviceId, accessToken) {
  * @return {Promise}
  */
 TestClient.prototype.start = function(existingDevices) {
-    let self = this;
+    const self = this;
 
     this.httpBackend.when("GET", "/pushrules").respond(200, {});
     this.httpBackend.when("POST", "/filter").respond(200, { filter_id: "fid" });
@@ -115,7 +115,7 @@ TestClient.prototype.stop = function() {
  * @return {string} base64 device key
  */
 TestClient.prototype.getDeviceKey = function() {
-    let keyId = 'curve25519:' + this.deviceId;
+    const keyId = 'curve25519:' + this.deviceId;
     return this.deviceKeys.keys[keyId];
 };
 
@@ -126,7 +126,7 @@ TestClient.prototype.getDeviceKey = function() {
  * @return {string} base64 device key
  */
 TestClient.prototype.getSigningKey = function() {
-    let keyId = 'ed25519:' + this.deviceId;
+    const keyId = 'ed25519:' + this.deviceId;
     return this.deviceKeys.keys[keyId];
 };
 
@@ -138,10 +138,10 @@ TestClient.prototype.getSigningKey = function() {
  * @return {Olm.Session}
  */
 function createOlmSession(olmAccount, recipientTestClient) {
-    let otkId = utils.keys(recipientTestClient.oneTimeKeys)[0];
-    let otk = recipientTestClient.oneTimeKeys[otkId];
+    const otkId = utils.keys(recipientTestClient.oneTimeKeys)[0];
+    const otk = recipientTestClient.oneTimeKeys[otkId];
 
-    let session = new Olm.Session();
+    const session = new Olm.Session();
     session.create_outbound(
         olmAccount, recipientTestClient.getDeviceKey(), otk.key
     );
@@ -166,7 +166,7 @@ function encryptOlmEvent(opts) {
     expect(opts.p2pSession).toBeDefined();
     expect(opts.recipient).toBeDefined();
 
-    let plaintext = {
+    const plaintext = {
         content: opts.plaincontent || {},
         recipient: opts.recipient.userId,
         recipient_keys: {
@@ -176,7 +176,7 @@ function encryptOlmEvent(opts) {
         type: opts.plaintype || 'm.test',
     };
 
-    let event = {
+    const event = {
         content: {
             algorithm: 'm.olm.v1.curve25519-aes-sha2',
             ciphertext: {},
@@ -205,7 +205,7 @@ function encryptMegolmEvent(opts) {
     expect(opts.senderKey).toBeDefined();
     expect(opts.groupSession).toBeDefined();
 
-    let plaintext = opts.plaintext || {};
+    const plaintext = opts.plaintext || {};
     if (!plaintext.content) {
         plaintext.content = {
             body: '42',
@@ -268,7 +268,7 @@ function encryptGroupSessionKey(opts) {
  * @return {object} event
  */
 function getSyncResponse(roomMembers) {
-    let roomResponse = {
+    const roomResponse = {
         state: {
             events: [
                 testUtils.mkEvent({
@@ -291,7 +291,7 @@ function getSyncResponse(roomMembers) {
         );
     }
 
-    let syncResponse = {
+    const syncResponse = {
         next_batch: 1,
         rooms: {
             join: {},
@@ -319,8 +319,8 @@ describe("megolm", function() {
      * @returns {Object} The fake query response
      */
     function getTestKeysQueryResponse(userId) {
-        let testE2eKeys = JSON.parse(testOlmAccount.identity_keys());
-        let testDeviceKeys = {
+        const testE2eKeys = JSON.parse(testOlmAccount.identity_keys());
+        const testDeviceKeys = {
             algorithms: ['m.olm.v1.curve25519-aes-sha2', 'm.megolm.v1.aes-sha2'],
             device_id: 'DEVICE_ID',
             keys: {
@@ -329,14 +329,14 @@ describe("megolm", function() {
             },
             user_id: userId,
         };
-        let j = anotherjson.stringify(testDeviceKeys);
-        let sig = testOlmAccount.sign(j);
+        const j = anotherjson.stringify(testDeviceKeys);
+        const sig = testOlmAccount.sign(j);
         testDeviceKeys.signatures = {};
         testDeviceKeys.signatures[userId] = {
             'ed25519:DEVICE_ID': sig,
         };
 
-        let queryResponse = {
+        const queryResponse = {
             device_keys: {},
         };
 
@@ -356,22 +356,22 @@ describe("megolm", function() {
      */
     function getTestKeysClaimResponse(userId) {
         testOlmAccount.generate_one_time_keys(1);
-        let testOneTimeKeys = JSON.parse(testOlmAccount.one_time_keys());
+        const testOneTimeKeys = JSON.parse(testOlmAccount.one_time_keys());
         testOlmAccount.mark_keys_as_published();
 
-        let keyId = utils.keys(testOneTimeKeys.curve25519)[0];
-        let oneTimeKey = testOneTimeKeys.curve25519[keyId];
-        let keyResult = {
+        const keyId = utils.keys(testOneTimeKeys.curve25519)[0];
+        const oneTimeKey = testOneTimeKeys.curve25519[keyId];
+        const keyResult = {
             'key': oneTimeKey,
         };
-        let j = anotherjson.stringify(keyResult);
-        let sig = testOlmAccount.sign(j);
+        const j = anotherjson.stringify(keyResult);
+        const sig = testOlmAccount.sign(j);
         keyResult.signatures = {};
         keyResult.signatures[userId] = {
             'ed25519:DEVICE_ID': sig,
         };
 
-        let claimResponse = {one_time_keys: {}};
+        const claimResponse = {one_time_keys: {}};
         claimResponse.one_time_keys[userId] = {
             'DEVICE_ID': {},
         };
@@ -389,7 +389,7 @@ describe("megolm", function() {
 
         testOlmAccount = new Olm.Account();
         testOlmAccount.create();
-        let testE2eKeys = JSON.parse(testOlmAccount.identity_keys());
+        const testE2eKeys = JSON.parse(testOlmAccount.identity_keys());
         testSenderKey = testE2eKeys.curve25519;
     });
 
@@ -399,13 +399,13 @@ describe("megolm", function() {
 
     it("Alice receives a megolm message", function(done) {
         return aliceTestClient.start().then(function() {
-            let p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
+            const p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
 
-            let groupSession = new Olm.OutboundGroupSession();
+            const groupSession = new Olm.OutboundGroupSession();
             groupSession.create();
 
             // make the room_key event
-            let roomKeyEncrypted = encryptGroupSessionKey({
+            const roomKeyEncrypted = encryptGroupSessionKey({
                 senderKey: testSenderKey,
                 recipient: aliceTestClient,
                 p2pSession: p2pSession,
@@ -414,14 +414,14 @@ describe("megolm", function() {
             });
 
             // encrypt a message with the group session
-            let messageEncrypted = encryptMegolmEvent({
+            const messageEncrypted = encryptMegolmEvent({
                 senderKey: testSenderKey,
                 groupSession: groupSession,
                 room_id: ROOM_ID,
             });
 
             // Alice gets both the events in a single sync
-            let syncResponse = {
+            const syncResponse = {
                 next_batch: 1,
                 to_device: {
                     events: [roomKeyEncrypted],
@@ -439,21 +439,21 @@ describe("megolm", function() {
             aliceTestClient.httpBackend.when("GET", "/sync").respond(200, syncResponse);
             return aliceTestClient.httpBackend.flush("/sync", 1);
         }).then(function() {
-            let room = aliceTestClient.client.getRoom(ROOM_ID);
-            let event = room.getLiveTimeline().getEvents()[0];
+            const room = aliceTestClient.client.getRoom(ROOM_ID);
+            const event = room.getLiveTimeline().getEvents()[0];
             expect(event.getContent().body).toEqual('42');
         }).nodeify(done);
     });
 
     it("Alice gets a second room_key message", function(done) {
         return aliceTestClient.start().then(function() {
-            let p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
+            const p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
 
-            let groupSession = new Olm.OutboundGroupSession();
+            const groupSession = new Olm.OutboundGroupSession();
             groupSession.create();
 
             // make the room_key event
-            let roomKeyEncrypted1 = encryptGroupSessionKey({
+            const roomKeyEncrypted1 = encryptGroupSessionKey({
                 senderKey: testSenderKey,
                 recipient: aliceTestClient,
                 p2pSession: p2pSession,
@@ -462,7 +462,7 @@ describe("megolm", function() {
             });
 
             // encrypt a message with the group session
-            let messageEncrypted = encryptMegolmEvent({
+            const messageEncrypted = encryptMegolmEvent({
                 senderKey: testSenderKey,
                 groupSession: groupSession,
                 room_id: ROOM_ID,
@@ -470,7 +470,7 @@ describe("megolm", function() {
 
             // make a second room_key event now that we have advanced the group
             // session.
-            let roomKeyEncrypted2 = encryptGroupSessionKey({
+            const roomKeyEncrypted2 = encryptGroupSessionKey({
                 senderKey: testSenderKey,
                 recipient: aliceTestClient,
                 p2pSession: p2pSession,
@@ -489,7 +489,7 @@ describe("megolm", function() {
             // on the second sync, send the advanced room key, along with the
             // message.  This simulates the situation where Alice has been sent a
             // later copy of the room key and is reloading the client.
-            let syncResponse2 = {
+            const syncResponse2 = {
                 next_batch: 2,
                 to_device: {
                     events: [roomKeyEncrypted2],
@@ -507,8 +507,8 @@ describe("megolm", function() {
 
             return aliceTestClient.httpBackend.flush("/sync", 2);
         }).then(function() {
-            let room = aliceTestClient.client.getRoom(ROOM_ID);
-            let event = room.getLiveTimeline().getEvents()[0];
+            const room = aliceTestClient.client.getRoom(ROOM_ID);
+            const event = room.getLiveTimeline().getEvents()[0];
             expect(event.getContent().body).toEqual('42');
         }).nodeify(done);
     });
@@ -517,12 +517,12 @@ describe("megolm", function() {
         let p2pSession;
 
         return aliceTestClient.start().then(function() {
-            let syncResponse = getSyncResponse(['@bob:xyz']);
+            const syncResponse = getSyncResponse(['@bob:xyz']);
 
             // establish an olm session with alice
             p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
 
-            let olmEvent = encryptOlmEvent({
+            const olmEvent = encryptOlmEvent({
                 senderKey: testSenderKey,
                 recipient: aliceTestClient,
                 p2pSession: p2pSession,
@@ -541,9 +541,9 @@ describe("megolm", function() {
             aliceTestClient.httpBackend.when(
                 'PUT', '/sendToDevice/m.room.encrypted/'
             ).respond(200, function(path, content) {
-                let m = content.messages['@bob:xyz'].DEVICE_ID;
-                let ct = m.ciphertext[testSenderKey];
-                let decrypted = JSON.parse(p2pSession.decrypt(ct.type, ct.body));
+                const m = content.messages['@bob:xyz'].DEVICE_ID;
+                const ct = m.ciphertext[testSenderKey];
+                const decrypted = JSON.parse(p2pSession.decrypt(ct.type, ct.body));
 
                 expect(decrypted.type).toEqual('m.room_key');
                 inboundGroupSession = new Olm.InboundGroupSession();
@@ -554,12 +554,12 @@ describe("megolm", function() {
             aliceTestClient.httpBackend.when(
                 'PUT', '/send/'
             ).respond(200, function(path, content) {
-                let ct = content.ciphertext;
-                let r = inboundGroupSession.decrypt(ct);
+                const ct = content.ciphertext;
+                const r = inboundGroupSession.decrypt(ct);
                 console.log('Decrypted received megolm message', r);
 
                 expect(r.message_index).toEqual(0);
-                let decrypted = JSON.parse(r.plaintext);
+                const decrypted = JSON.parse(r.plaintext);
                 expect(decrypted.type).toEqual('m.room.message');
                 expect(decrypted.content.body).toEqual('test');
 
@@ -577,7 +577,7 @@ describe("megolm", function() {
 
     it("Alice shouldn't do a second /query for non-e2e-capable devices", function(done) {
         return aliceTestClient.start().then(function() {
-            let syncResponse = getSyncResponse(['@bob:xyz']);
+            const syncResponse = getSyncResponse(['@bob:xyz']);
             aliceTestClient.httpBackend.when('GET', '/sync').respond(200, syncResponse);
 
             return aliceTestClient.httpBackend.flush('/sync', 1);
@@ -613,12 +613,12 @@ describe("megolm", function() {
 
     it("We shouldn't attempt to send to blocked devices", function(done) {
         return aliceTestClient.start().then(function() {
-            let syncResponse = getSyncResponse(['@bob:xyz']);
+            const syncResponse = getSyncResponse(['@bob:xyz']);
 
             // establish an olm session with alice
-            let p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
+            const p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
 
-            let olmEvent = encryptOlmEvent({
+            const olmEvent = encryptOlmEvent({
                 senderKey: testSenderKey,
                 recipient: aliceTestClient,
                 p2pSession: p2pSession,
@@ -662,12 +662,12 @@ describe("megolm", function() {
         let megolmSessionId;
 
         return aliceTestClient.start().then(function() {
-            let syncResponse = getSyncResponse(['@bob:xyz']);
+            const syncResponse = getSyncResponse(['@bob:xyz']);
 
             // establish an olm session with alice
             p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
 
-            let olmEvent = encryptOlmEvent({
+            const olmEvent = encryptOlmEvent({
                 senderKey: testSenderKey,
                 recipient: aliceTestClient,
                 p2pSession: p2pSession,
@@ -688,10 +688,10 @@ describe("megolm", function() {
                 'PUT', '/sendToDevice/m.room.encrypted/'
             ).respond(200, function(path, content) {
                 console.log('sendToDevice: ', content);
-                let m = content.messages['@bob:xyz'].DEVICE_ID;
-                let ct = m.ciphertext[testSenderKey];
+                const m = content.messages['@bob:xyz'].DEVICE_ID;
+                const ct = m.ciphertext[testSenderKey];
                 expect(ct.type).toEqual(1); // normal message
-                let decrypted = JSON.parse(p2pSession.decrypt(ct.type, ct.body));
+                const decrypted = JSON.parse(p2pSession.decrypt(ct.type, ct.body));
                 console.log('decrypted sendToDevice:', decrypted);
                 expect(decrypted.type).toEqual('m.room_key');
                 megolmSessionId = decrypted.content.session_id;
@@ -747,7 +747,7 @@ describe("megolm", function() {
             getTestKeysQueryResponse(aliceTestClient.userId)
         ).then(function() {
             // an encrypted room with just alice
-            let syncResponse = {
+            const syncResponse = {
                 next_batch: 1,
                 rooms: {
                     join: {},
@@ -785,13 +785,13 @@ describe("megolm", function() {
                 'PUT', '/sendToDevice/m.room.encrypted/'
             ).respond(200, function(path, content) {
                 console.log("sendToDevice: ", content);
-                let m = content.messages[aliceTestClient.userId].DEVICE_ID;
-                let ct = m.ciphertext[testSenderKey];
+                const m = content.messages[aliceTestClient.userId].DEVICE_ID;
+                const ct = m.ciphertext[testSenderKey];
                 expect(ct.type).toEqual(0); // pre-key message
 
                 p2pSession = new Olm.Session();
                 p2pSession.create_inbound(testOlmAccount, ct.body);
-                let decrypted = JSON.parse(p2pSession.decrypt(ct.type, ct.body));
+                const decrypted = JSON.parse(p2pSession.decrypt(ct.type, ct.body));
 
                 expect(decrypted.type).toEqual('m.room_key');
                 inboundGroupSession = new Olm.InboundGroupSession();
@@ -802,8 +802,8 @@ describe("megolm", function() {
             aliceTestClient.httpBackend.when(
                 'PUT', '/send/'
             ).respond(200, function(path, content) {
-                let ct = content.ciphertext;
-                let r = inboundGroupSession.decrypt(ct);
+                const ct = content.ciphertext;
+                const r = inboundGroupSession.decrypt(ct);
                 console.log('Decrypted received megolm message', r);
                 decrypted = JSON.parse(r.plaintext);
 
@@ -834,9 +834,9 @@ describe("megolm", function() {
         aliceTestClient.httpBackend.when(
             'PUT', '/sendToDevice/m.room.encrypted/'
         ).respond(200, function(path, content) {
-            let m = content.messages['@bob:xyz'].DEVICE_ID;
-            let ct = m.ciphertext[testSenderKey];
-            let decrypted = JSON.parse(p2pSession.decrypt(ct.type, ct.body));
+            const m = content.messages['@bob:xyz'].DEVICE_ID;
+            const ct = m.ciphertext[testSenderKey];
+            const decrypted = JSON.parse(p2pSession.decrypt(ct.type, ct.body));
 
             expect(decrypted.type).toEqual('m.room_key');
             inboundGroupSession = new Olm.InboundGroupSession();
@@ -847,12 +847,12 @@ describe("megolm", function() {
         aliceTestClient.httpBackend.when(
             'PUT', '/send/'
         ).respond(200, function(path, content) {
-            let ct = content.ciphertext;
-            let r = inboundGroupSession.decrypt(ct);
+            const ct = content.ciphertext;
+            const r = inboundGroupSession.decrypt(ct);
             console.log('Decrypted received megolm message', r);
 
             expect(r.message_index).toEqual(0);
-            let decrypted = JSON.parse(r.plaintext);
+            const decrypted = JSON.parse(r.plaintext);
             expect(decrypted.type).toEqual('m.room.message');
             expect(decrypted.content.body).toEqual('test');
 
@@ -862,12 +862,12 @@ describe("megolm", function() {
         });
 
         return aliceTestClient.start().then(function() {
-            let syncResponse = getSyncResponse(['@bob:xyz']);
+            const syncResponse = getSyncResponse(['@bob:xyz']);
 
             // establish an olm session with alice
             p2pSession = createOlmSession(testOlmAccount, aliceTestClient);
 
-            let olmEvent = encryptOlmEvent({
+            const olmEvent = encryptOlmEvent({
                 senderKey: testSenderKey,
                 recipient: aliceTestClient,
                 p2pSession: p2pSession,
diff --git a/spec/mock-request.js b/spec/mock-request.js
index 5c9366fce..9229fd662 100644
--- a/spec/mock-request.js
+++ b/spec/mock-request.js
@@ -1,5 +1,5 @@
 "use strict";
-let q = require("q");
+const q = require("q");
 
 /**
  * Construct a mock HTTP backend, heavily inspired by Angular.js.
@@ -8,15 +8,15 @@ let q = require("q");
 function HttpBackend() {
     this.requests = [];
     this.expectedRequests = [];
-    let self = this;
+    const self = this;
     // the request function dependency that the SDK needs.
     this.requestFn = function(opts, callback) {
-        let req = new Request(opts, callback);
+        const req = new Request(opts, callback);
         console.log("HTTP backend received request: %s", req);
         self.requests.push(req);
 
-        let abort = function() {
-            let idx = self.requests.indexOf(req);
+        const abort = function() {
+            const idx = self.requests.indexOf(req);
             if (idx >= 0) {
                 console.log("Aborting HTTP request: %s %s", opts.method,
                             opts.uri);
@@ -38,14 +38,14 @@ HttpBackend.prototype = {
      * @return {Promise} resolved when there is nothing left to flush.
      */
     flush: function(path, numToFlush) {
-        let defer = q.defer();
-        let self = this;
+        const defer = q.defer();
+        const self = this;
         let flushed = 0;
         let triedWaiting = false;
         console.log(
             "HTTP backend flushing... (path=%s  numToFlush=%s)", path, numToFlush
         );
-        let tryFlush = function() {
+        const tryFlush = function() {
             // if there's more real requests and more expected requests, flush 'em.
             console.log(
                 "  trying to flush queue => reqs=%s expected=%s [%s]",
@@ -137,7 +137,7 @@ HttpBackend.prototype = {
      * Makes sure that the SDK hasn't sent any more requests to the backend.
      */
     verifyNoOutstandingRequests: function() {
-        let firstOutstandingReq = this.requests[0] || {};
+        const firstOutstandingReq = this.requests[0] || {};
         expect(this.requests.length).toEqual(0,
             "Expected no more HTTP requests but received request to " +
             firstOutstandingReq.path
@@ -148,7 +148,7 @@ HttpBackend.prototype = {
      * Makes sure that the test doesn't have any unresolved requests.
      */
     verifyNoOutstandingExpectation: function() {
-        let firstOutstandingExpectation = this.expectedRequests[0] || {};
+        const firstOutstandingExpectation = this.expectedRequests[0] || {};
         expect(this.expectedRequests.length).toEqual(0,
             "Expected to see HTTP request for " + firstOutstandingExpectation.path
         );
@@ -162,7 +162,7 @@ HttpBackend.prototype = {
      * @return {Request} An expected request.
      */
     when: function(method, path, data) {
-        let pendingReq = new ExpectedRequest(method, path, data);
+        const pendingReq = new ExpectedRequest(method, path, data);
         this.expectedRequests.push(pendingReq);
         return pendingReq;
     },
diff --git a/spec/test-utils.js b/spec/test-utils.js
index d05e5004b..718c672ed 100644
--- a/spec/test-utils.js
+++ b/spec/test-utils.js
@@ -1,6 +1,6 @@
 "use strict";
-let sdk = require("..");
-let MatrixEvent = sdk.MatrixEvent;
+const sdk = require("..");
+const MatrixEvent = sdk.MatrixEvent;
 
 /**
  * Perform common actions before each test case, e.g. printing the test case
@@ -8,7 +8,7 @@ let MatrixEvent = sdk.MatrixEvent;
  * @param {TestCase} testCase The test case that is about to be run.
  */
 module.exports.beforeEach = function(testCase) {
-    let desc = testCase.suite.description + " : " + testCase.description;
+    const desc = testCase.suite.description + " : " + testCase.description;
     console.log(desc);
     console.log(new Array(1 + desc.length).join("="));
 };
@@ -22,13 +22,13 @@ module.exports.beforeEach = function(testCase) {
 module.exports.mock = function(constr, name) {
     // By Tim Buschtöns
     // http://eclipsesource.com/blogs/2014/03/27/mocks-in-jasmine-tests/
-    let HelperConstr = new Function(); // jshint ignore:line
+    const HelperConstr = new Function(); // jshint ignore:line
     HelperConstr.prototype = constr.prototype;
-    let result = new HelperConstr();
+    const result = new HelperConstr();
     result.jasmineToString = function() {
         return "mock" + (name ? " of " + name : "");
     };
-    for (let key in constr.prototype) { // eslint-disable-line guard-for-in
+    for (const key in constr.prototype) { // eslint-disable-line guard-for-in
         try {
             if (constr.prototype[key] instanceof Function) {
                 result[key] = jasmine.createSpy((name || "mock") + '.' + key);
@@ -57,7 +57,7 @@ module.exports.mkEvent = function(opts) {
     if (!opts.type || !opts.content) {
         throw new Error("Missing .type or .content =>" + JSON.stringify(opts));
     }
-    let event = {
+    const event = {
         type: opts.type,
         room_id: opts.room,
         sender: opts.sender || opts.user, // opts.user for backwards-compat
@@ -83,7 +83,7 @@ module.exports.mkPresence = function(opts) {
     if (!opts.user) {
         throw new Error("Missing user");
     }
-    let event = {
+    const event = {
         event_id: "$" + Math.random() + "-" + Math.random(),
         type: "m.presence",
         sender: opts.sender || opts.user, // opts.user for backwards-compat
diff --git a/spec/unit/content-repo.spec.js b/spec/unit/content-repo.spec.js
index de8e6fb3c..383002406 100644
--- a/spec/unit/content-repo.spec.js
+++ b/spec/unit/content-repo.spec.js
@@ -1,9 +1,9 @@
 "use strict";
-let ContentRepo = require("../../lib/content-repo");
-let testUtils = require("../test-utils");
+const ContentRepo = require("../../lib/content-repo");
+const testUtils = require("../test-utils");
 
 describe("ContentRepo", function() {
-    let baseUrl = "https://my.home.server";
+    const baseUrl = "https://my.home.server";
 
     beforeEach(function() {
         testUtils.beforeEach(this); // eslint-disable-line no-invalid-this
@@ -11,7 +11,7 @@ describe("ContentRepo", function() {
 
     describe("getHttpUriForMxc", function() {
         it("should do nothing to HTTP URLs when allowing direct links", function() {
-            let httpUrl = "http://example.com/image.jpeg";
+            const httpUrl = "http://example.com/image.jpeg";
             expect(
                 ContentRepo.getHttpUriForMxc(
                     baseUrl, httpUrl, undefined, undefined, undefined, true
@@ -20,13 +20,13 @@ describe("ContentRepo", function() {
         });
 
         it("should return the empty string HTTP URLs by default", function() {
-            let httpUrl = "http://example.com/image.jpeg";
+            const httpUrl = "http://example.com/image.jpeg";
             expect(ContentRepo.getHttpUriForMxc(baseUrl, httpUrl)).toEqual("");
         });
 
         it("should return a download URL if no width/height/resize are specified",
         function() {
-            let mxcUri = "mxc://server.name/resourceid";
+            const mxcUri = "mxc://server.name/resourceid";
             expect(ContentRepo.getHttpUriForMxc(baseUrl, mxcUri)).toEqual(
                 baseUrl + "/_matrix/media/v1/download/server.name/resourceid"
             );
@@ -38,7 +38,7 @@ describe("ContentRepo", function() {
 
         it("should return a thumbnail URL if a width/height/resize is specified",
         function() {
-            let mxcUri = "mxc://server.name/resourceid";
+            const mxcUri = "mxc://server.name/resourceid";
             expect(ContentRepo.getHttpUriForMxc(baseUrl, mxcUri, 32, 64, "crop")).toEqual(
                 baseUrl + "/_matrix/media/v1/thumbnail/server.name/resourceid" +
                 "?width=32&height=64&method=crop"
@@ -47,7 +47,7 @@ describe("ContentRepo", function() {
 
         it("should put fragments from mxc:// URIs after any query parameters",
         function() {
-            let mxcUri = "mxc://server.name/resourceid#automade";
+            const mxcUri = "mxc://server.name/resourceid#automade";
             expect(ContentRepo.getHttpUriForMxc(baseUrl, mxcUri, 32)).toEqual(
                 baseUrl + "/_matrix/media/v1/thumbnail/server.name/resourceid" +
                 "?width=32#automade"
@@ -56,7 +56,7 @@ describe("ContentRepo", function() {
 
         it("should put fragments from mxc:// URIs at the end of the HTTP URI",
         function() {
-            let mxcUri = "mxc://server.name/resourceid#automade";
+            const mxcUri = "mxc://server.name/resourceid#automade";
             expect(ContentRepo.getHttpUriForMxc(baseUrl, mxcUri)).toEqual(
                 baseUrl + "/_matrix/media/v1/download/server.name/resourceid#automade"
             );
diff --git a/spec/unit/crypto.spec.js b/spec/unit/crypto.spec.js
index bde8c6c8b..eb0747d3d 100644
--- a/spec/unit/crypto.spec.js
+++ b/spec/unit/crypto.spec.js
@@ -1,7 +1,7 @@
 
 "use strict";
-let Crypto = require("../../lib/crypto");
-let sdk = require("../..");
+const Crypto = require("../../lib/crypto");
+const sdk = require("../..");
 
 describe("Crypto", function() {
     if (!sdk.CRYPTO_ENABLED) {
diff --git a/spec/unit/event-timeline.spec.js b/spec/unit/event-timeline.spec.js
index 9876b8c76..90e2b29f4 100644
--- a/spec/unit/event-timeline.spec.js
+++ b/spec/unit/event-timeline.spec.js
@@ -1,7 +1,7 @@
 "use strict";
-let sdk = require("../..");
-let EventTimeline = sdk.EventTimeline;
-let utils = require("../test-utils");
+const sdk = require("../..");
+const EventTimeline = sdk.EventTimeline;
+const utils = require("../test-utils");
 
 function mockRoomStates(timeline) {
     timeline._startState = utils.mock(sdk.RoomState, "startState");
@@ -9,16 +9,16 @@ function mockRoomStates(timeline) {
 }
 
 describe("EventTimeline", function() {
-    let roomId = "!foo:bar";
-    let userA = "@alice:bar";
-    let userB = "@bertha:bar";
+    const roomId = "!foo:bar";
+    const userA = "@alice:bar";
+    const userB = "@bertha:bar";
     let timeline;
 
     beforeEach(function() {
         utils.beforeEach(this); // eslint-disable-line no-invalid-this
 
         // XXX: this is a horrid hack; should use sinon or something instead to mock
-        let timelineSet = { room: { roomId: roomId }};
+        const timelineSet = { room: { roomId: roomId }};
         timelineSet.room.getUnfilteredTimelineSet = function() {
             return timelineSet;
         };
@@ -28,7 +28,7 @@ describe("EventTimeline", function() {
 
     describe("construction", function() {
         it("getRoomId should get room id", function() {
-            let v = timeline.getRoomId();
+            const v = timeline.getRoomId();
             expect(v).toEqual(roomId);
         });
     });
@@ -39,7 +39,7 @@ describe("EventTimeline", function() {
         });
 
         it("should copy state events to start and end state", function() {
-            let events = [
+            const events = [
                 utils.mkMembership({
                     room: roomId, mship: "invite", user: userB, skey: userA,
                     event: true,
@@ -60,13 +60,13 @@ describe("EventTimeline", function() {
         });
 
         it("should raise an exception if called after events are added", function() {
-            let event =
+            const event =
                 utils.mkMessage({
                     room: roomId, user: userA, msg: "Adam stole the plushies",
                     event: true,
                 });
 
-            let state = [
+            const state = [
                 utils.mkMembership({
                     room: roomId, mship: "invite", user: userB, skey: userA,
                     event: true,
@@ -105,8 +105,8 @@ describe("EventTimeline", function() {
         });
 
         it("setNeighbouringTimeline should set neighbour", function() {
-            let prev = {a: "a"};
-            let next = {b: "b"};
+            const prev = {a: "a"};
+            const next = {b: "b"};
             timeline.setNeighbouringTimeline(prev, EventTimeline.BACKWARDS);
             timeline.setNeighbouringTimeline(next, EventTimeline.FORWARDS);
             expect(timeline.getNeighbouringTimeline(EventTimeline.BACKWARDS)).toBe(prev);
@@ -114,8 +114,8 @@ describe("EventTimeline", function() {
         });
 
         it("setNeighbouringTimeline should throw if called twice", function() {
-            let prev = {a: "a"};
-            let next = {b: "b"};
+            const prev = {a: "a"};
+            const next = {b: "b"};
             expect(function() {
                 timeline.setNeighbouringTimeline(prev, EventTimeline.BACKWARDS);
             }).not.toThrow();
@@ -141,7 +141,7 @@ describe("EventTimeline", function() {
             mockRoomStates(timeline);
         });
 
-        let events = [
+        const events = [
             utils.mkMessage({
                 room: roomId, user: userA, msg: "hungry hungry hungry",
                 event: true,
@@ -154,7 +154,7 @@ describe("EventTimeline", function() {
 
         it("should be able to add events to the end", function() {
             timeline.addEvent(events[0], false);
-            let initialIndex = timeline.getBaseIndex();
+            const initialIndex = timeline.getBaseIndex();
             timeline.addEvent(events[1], false);
             expect(timeline.getBaseIndex()).toEqual(initialIndex);
             expect(timeline.getEvents().length).toEqual(2);
@@ -164,7 +164,7 @@ describe("EventTimeline", function() {
 
         it("should be able to add events to the start", function() {
             timeline.addEvent(events[0], true);
-            let initialIndex = timeline.getBaseIndex();
+            const initialIndex = timeline.getBaseIndex();
             timeline.addEvent(events[1], true);
             expect(timeline.getBaseIndex()).toEqual(initialIndex + 1);
             expect(timeline.getEvents().length).toEqual(2);
@@ -173,12 +173,12 @@ describe("EventTimeline", function() {
         });
 
         it("should set event.sender for new and old events", function() {
-            let sentinel = {
+            const sentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Alice",
             };
-            let oldSentinel = {
+            const oldSentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Old Alice",
@@ -198,11 +198,11 @@ describe("EventTimeline", function() {
                     return null;
                 });
 
-            let newEv = utils.mkEvent({
+            const newEv = utils.mkEvent({
                 type: "m.room.name", room: roomId, user: userA, event: true,
                 content: { name: "New Room Name" },
             });
-            let oldEv = utils.mkEvent({
+            const oldEv = utils.mkEvent({
                 type: "m.room.name", room: roomId, user: userA, event: true,
                 content: { name: "Old Room Name" },
             });
@@ -215,12 +215,12 @@ describe("EventTimeline", function() {
 
         it("should set event.target for new and old m.room.member events",
         function() {
-            let sentinel = {
+            const sentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Alice",
             };
-            let oldSentinel = {
+            const oldSentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Old Alice",
@@ -240,10 +240,10 @@ describe("EventTimeline", function() {
                     return null;
                 });
 
-            let newEv = utils.mkMembership({
+            const newEv = utils.mkMembership({
                 room: roomId, mship: "invite", user: userB, skey: userA, event: true,
             });
-            let oldEv = utils.mkMembership({
+            const oldEv = utils.mkMembership({
                 room: roomId, mship: "ban", user: userB, skey: userA, event: true,
             });
             timeline.addEvent(newEv, false);
@@ -254,7 +254,7 @@ describe("EventTimeline", function() {
 
         it("should call setStateEvents on the right RoomState with the right " +
            "forwardLooking value for new events", function() {
-            let events = [
+            const events = [
                 utils.mkMembership({
                     room: roomId, mship: "invite", user: userB, skey: userA, event: true,
                 }),
@@ -284,7 +284,7 @@ describe("EventTimeline", function() {
 
         it("should call setStateEvents on the right RoomState with the right " +
            "forwardLooking value for old events", function() {
-            let events = [
+            const events = [
                 utils.mkMembership({
                     room: roomId, mship: "invite", user: userB, skey: userA, event: true,
                 }),
@@ -313,7 +313,7 @@ describe("EventTimeline", function() {
     });
 
     describe("removeEvent", function() {
-        let events = [
+        const events = [
             utils.mkMessage({
                 room: roomId, user: userA, msg: "hungry hungry hungry",
                 event: true,
@@ -365,7 +365,7 @@ describe("EventTimeline", function() {
            function() {
                timeline.addEvent(events[0], true);
                timeline.removeEvent(events[0].getId());
-               let initialIndex = timeline.getBaseIndex();
+               const initialIndex = timeline.getBaseIndex();
                timeline.addEvent(events[1], false);
                timeline.addEvent(events[2], false);
                expect(timeline.getBaseIndex()).toEqual(initialIndex);
diff --git a/spec/unit/filter.spec.js b/spec/unit/filter.spec.js
index 527db651f..9a28c2b03 100644
--- a/spec/unit/filter.spec.js
+++ b/spec/unit/filter.spec.js
@@ -1,11 +1,11 @@
 "use strict";
-let sdk = require("../..");
-let Filter = sdk.Filter;
-let utils = require("../test-utils");
+const sdk = require("../..");
+const Filter = sdk.Filter;
+const utils = require("../test-utils");
 
 describe("Filter", function() {
-    let filterId = "f1lt3ring15g00d4ursoul";
-    let userId = "@sir_arthur_david:humming.tiger";
+    const filterId = "f1lt3ring15g00d4ursoul";
+    const userId = "@sir_arthur_david:humming.tiger";
     let filter;
 
     beforeEach(function() {
@@ -15,10 +15,10 @@ describe("Filter", function() {
 
     describe("fromJson", function() {
         it("create a new Filter from the provided values", function() {
-            let definition = {
+            const definition = {
                 event_fields: ["type", "content"],
             };
-            let f = Filter.fromJson(userId, filterId, definition);
+            const f = Filter.fromJson(userId, filterId, definition);
             expect(f.getDefinition()).toEqual(definition);
             expect(f.userId).toEqual(userId);
             expect(f.filterId).toEqual(filterId);
@@ -40,7 +40,7 @@ describe("Filter", function() {
 
     describe("setDefinition/getDefinition", function() {
         it("should set and get the filter body", function() {
-            let definition = {
+            const definition = {
                 event_format: "client",
             };
             filter.setDefinition(definition);
diff --git a/spec/unit/interactive-auth.spec.js b/spec/unit/interactive-auth.spec.js
index b03dd0629..5c783db3d 100644
--- a/spec/unit/interactive-auth.spec.js
+++ b/spec/unit/interactive-auth.spec.js
@@ -15,12 +15,12 @@ limitations under the License.
 */
 "use strict";
 
-let q = require("q");
-let sdk = require("../..");
-let utils = require("../test-utils");
+const q = require("q");
+const sdk = require("../..");
+const utils = require("../test-utils");
 
-let InteractiveAuth = sdk.InteractiveAuth;
-let MatrixError = sdk.MatrixError;
+const InteractiveAuth = sdk.InteractiveAuth;
+const MatrixError = sdk.MatrixError;
 
 describe("InteractiveAuth", function() {
     beforeEach(function() {
@@ -28,10 +28,10 @@ describe("InteractiveAuth", function() {
     });
 
     it("should start an auth stage and complete it", function(done) {
-        let doRequest = jasmine.createSpy('doRequest');
-        let startAuthStage = jasmine.createSpy('startAuthStage');
+        const doRequest = jasmine.createSpy('doRequest');
+        const startAuthStage = jasmine.createSpy('startAuthStage');
 
-        let ia = new InteractiveAuth({
+        const ia = new InteractiveAuth({
             doRequest: doRequest,
             startAuthStage: startAuthStage,
             authData: {
@@ -60,7 +60,7 @@ describe("InteractiveAuth", function() {
         });
 
         // .. which should trigger a call here
-        let requestRes = {"a": "b"};
+        const requestRes = {"a": "b"};
         doRequest.andCallFake(function(authData) {
             expect(authData).toEqual({
                 session: "sessionId",
@@ -78,10 +78,10 @@ describe("InteractiveAuth", function() {
     });
 
     it("should make a request if no authdata is provided", function(done) {
-        let doRequest = jasmine.createSpy('doRequest');
-        let startAuthStage = jasmine.createSpy('startAuthStage');
+        const doRequest = jasmine.createSpy('doRequest');
+        const startAuthStage = jasmine.createSpy('startAuthStage');
 
-        let ia = new InteractiveAuth({
+        const ia = new InteractiveAuth({
             doRequest: doRequest,
             startAuthStage: startAuthStage,
         });
@@ -93,7 +93,7 @@ describe("InteractiveAuth", function() {
         doRequest.andCallFake(function(authData) {
             console.log("request1", authData);
             expect(authData).toBe(null);
-            let err = new MatrixError({
+            const err = new MatrixError({
                 session: "sessionId",
                 flows: [
                     { stages: ["logintype"] },
@@ -107,7 +107,7 @@ describe("InteractiveAuth", function() {
         });
 
         // .. which should be followed by a call to startAuthStage
-        let requestRes = {"a": "b"};
+        const requestRes = {"a": "b"};
         startAuthStage.andCallFake(function(stage) {
             expect(stage).toEqual("logintype");
             expect(ia.getSessionId()).toEqual("sessionId");
diff --git a/spec/unit/matrix-client.spec.js b/spec/unit/matrix-client.spec.js
index 11897cd7c..5990bcd67 100644
--- a/spec/unit/matrix-client.spec.js
+++ b/spec/unit/matrix-client.spec.js
@@ -1,40 +1,40 @@
 "use strict";
-let q = require("q");
-let sdk = require("../..");
-let MatrixClient = sdk.MatrixClient;
-let utils = require("../test-utils");
+const q = require("q");
+const sdk = require("../..");
+const MatrixClient = sdk.MatrixClient;
+const utils = require("../test-utils");
 
 describe("MatrixClient", function() {
-    let userId = "@alice:bar";
-    let identityServerUrl = "https://identity.server";
-    let identityServerDomain = "identity.server";
+    const userId = "@alice:bar";
+    const identityServerUrl = "https://identity.server";
+    const identityServerDomain = "identity.server";
     let client;
     let store;
     let scheduler;
 
-    let KEEP_ALIVE_PATH = "/_matrix/client/versions";
+    const KEEP_ALIVE_PATH = "/_matrix/client/versions";
 
-    let PUSH_RULES_RESPONSE = {
+    const PUSH_RULES_RESPONSE = {
         method: "GET",
         path: "/pushrules/",
         data: {},
     };
 
-    let FILTER_PATH = "/user/" + encodeURIComponent(userId) + "/filter";
+    const FILTER_PATH = "/user/" + encodeURIComponent(userId) + "/filter";
 
-    let FILTER_RESPONSE = {
+    const FILTER_RESPONSE = {
         method: "POST",
         path: FILTER_PATH,
         data: { filter_id: "f1lt3r" },
     };
 
-    let SYNC_DATA = {
+    const SYNC_DATA = {
         next_batch: "s_5_3",
         presence: { events: [] },
         rooms: {},
     };
 
-    let SYNC_RESPONSE = {
+    const SYNC_RESPONSE = {
         method: "GET",
         path: "/sync",
         data: SYNC_DATA,
@@ -59,8 +59,8 @@ describe("MatrixClient", function() {
         if (path === KEEP_ALIVE_PATH && acceptKeepalives) {
             return q();
         }
-        let next = httpLookups.shift();
-        let logLine = (
+        const next = httpLookups.shift();
+        const logLine = (
             "MatrixClient[UT] RECV " + method + " " + path + "  " +
             "EXPECT " + (next ? next.method : next) + " " + (next ? next.path : next)
         );
@@ -176,9 +176,9 @@ describe("MatrixClient", function() {
         httpLookups = [];
         httpLookups.push(PUSH_RULES_RESPONSE);
         httpLookups.push(SYNC_RESPONSE);
-        let filterId = "ehfewf";
+        const filterId = "ehfewf";
         store.getFilterIdByName.andReturn(filterId);
-        let filter = new sdk.Filter(0, filterId);
+        const filter = new sdk.Filter(0, filterId);
         filter.setDefinition({"room": {"timeline": {"limit": 8}}});
         store.getFilter.andReturn(filter);
         client.startClient();
@@ -220,7 +220,7 @@ describe("MatrixClient", function() {
                 // and they all need to be stored!
                 return "FILTER_SYNC_" + userId + (suffix ? "_" + suffix : "");
             }
-            let invalidFilterId = 'invalidF1lt3r';
+            const invalidFilterId = 'invalidF1lt3r';
             httpLookups = [];
             httpLookups.push({
                 method: "GET",
@@ -236,9 +236,9 @@ describe("MatrixClient", function() {
             httpLookups.push(FILTER_RESPONSE);
             store.getFilterIdByName.andReturn(invalidFilterId);
 
-            let filterName = getFilterName(client.credentials.userId);
+            const filterName = getFilterName(client.credentials.userId);
             client.store.setFilterIdByName(filterName, invalidFilterId);
-            let filter = new sdk.Filter(client.credentials.userId);
+            const filter = new sdk.Filter(client.credentials.userId);
 
             client.getOrCreateFilter(filterName, filter).then(function(filterId) {
                 expect(filterId).toEqual(FILTER_RESPONSE.data.filter_id);
@@ -332,7 +332,7 @@ describe("MatrixClient", function() {
     describe("emitted sync events", function() {
         function syncChecker(expectedStates, done) {
             return function syncListener(state, old) {
-                let expected = expectedStates.shift();
+                const expected = expectedStates.shift();
                 console.log(
                     "'sync' curr=%s old=%s EXPECT=%s", state, old, expected
                 );
@@ -352,14 +352,14 @@ describe("MatrixClient", function() {
         }
 
         it("should transition null -> PREPARED after the first /sync", function(done) {
-            let expectedStates = [];
+            const expectedStates = [];
             expectedStates.push(["PREPARED", null]);
             client.on("sync", syncChecker(expectedStates, done));
             client.startClient();
         });
 
         it("should transition null -> ERROR after a failed /filter", function(done) {
-            let expectedStates = [];
+            const expectedStates = [];
             httpLookups = [];
             httpLookups.push(PUSH_RULES_RESPONSE);
             httpLookups.push({
@@ -372,7 +372,7 @@ describe("MatrixClient", function() {
 
         it("should transition ERROR -> PREPARED after /sync if prev failed",
         function(done) {
-            let expectedStates = [];
+            const expectedStates = [];
             acceptKeepalives = false;
             httpLookups = [];
             httpLookups.push(PUSH_RULES_RESPONSE);
@@ -399,7 +399,7 @@ describe("MatrixClient", function() {
         });
 
         it("should transition PREPARED -> SYNCING after /sync", function(done) {
-            let expectedStates = [];
+            const expectedStates = [];
             expectedStates.push(["PREPARED", null]);
             expectedStates.push(["SYNCING", "PREPARED"]);
             client.on("sync", syncChecker(expectedStates, done));
@@ -408,7 +408,7 @@ describe("MatrixClient", function() {
 
         it("should transition SYNCING -> ERROR after a failed /sync", function(done) {
             acceptKeepalives = false;
-            let expectedStates = [];
+            const expectedStates = [];
             httpLookups.push({
                 method: "GET", path: "/sync", error: { errcode: "NONONONONO" },
             });
@@ -427,7 +427,7 @@ describe("MatrixClient", function() {
 
         xit("should transition ERROR -> SYNCING after /sync if prev failed",
         function(done) {
-            let expectedStates = [];
+            const expectedStates = [];
             httpLookups.push({
                 method: "GET", path: "/sync", error: { errcode: "NONONONONO" },
             });
@@ -442,7 +442,7 @@ describe("MatrixClient", function() {
 
         it("should transition SYNCING -> SYNCING on subsequent /sync successes",
         function(done) {
-            let expectedStates = [];
+            const expectedStates = [];
             httpLookups.push(SYNC_RESPONSE);
             httpLookups.push(SYNC_RESPONSE);
 
@@ -455,7 +455,7 @@ describe("MatrixClient", function() {
 
         it("should transition ERROR -> ERROR if keepalive keeps failing", function(done) {
             acceptKeepalives = false;
-            let expectedStates = [];
+            const expectedStates = [];
             httpLookups.push({
                 method: "GET", path: "/sync", error: { errcode: "NONONONONO" },
             });
@@ -479,7 +479,7 @@ describe("MatrixClient", function() {
     });
 
     describe("inviteByEmail", function() {
-        let roomId = "!foo:bar";
+        const roomId = "!foo:bar";
 
         it("should send an invite HTTP POST", function() {
             httpLookups = [{
diff --git a/spec/unit/pushprocessor.spec.js b/spec/unit/pushprocessor.spec.js
index f22fd5539..9c09771b5 100644
--- a/spec/unit/pushprocessor.spec.js
+++ b/spec/unit/pushprocessor.spec.js
@@ -1,18 +1,18 @@
 "use strict";
-let PushProcessor = require("../../lib/pushprocessor");
-let utils = require("../test-utils");
+const PushProcessor = require("../../lib/pushprocessor");
+const utils = require("../test-utils");
 
 describe('NotificationService', function() {
-    let testUserId = "@ali:matrix.org";
-    let testDisplayName = "Alice M";
-    let testRoomId = "!fl1bb13:localhost";
+    const testUserId = "@ali:matrix.org";
+    const testDisplayName = "Alice M";
+    const testRoomId = "!fl1bb13:localhost";
 
     let testEvent;
 
     let pushProcessor;
 
     // These would be better if individual rules were configured in the tests themselves.
-    let matrixClient = {
+    const matrixClient = {
         getRoom: function() {
             return {
                 currentState: {
@@ -213,25 +213,25 @@ describe('NotificationService', function() {
 
     it('should bing on a user ID.', function() {
         testEvent.event.content.body = "Hello @ali:matrix.org, how are you?";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
     it('should bing on a partial user ID with an @.', function() {
         testEvent.event.content.body = "Hello @ali, how are you?";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
     it('should bing on a partial user ID without @.', function() {
         testEvent.event.content.body = "Hello ali, how are you?";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
     it('should bing on a case-insensitive user ID.', function() {
         testEvent.event.content.body = "Hello @AlI:matrix.org, how are you?";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
@@ -239,13 +239,13 @@ describe('NotificationService', function() {
 
     it('should bing on a display name.', function() {
         testEvent.event.content.body = "Hello Alice M, how are you?";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
     it('should bing on a case-insensitive display name.', function() {
         testEvent.event.content.body = "Hello ALICE M, how are you?";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
@@ -253,19 +253,19 @@ describe('NotificationService', function() {
 
     it('should bing on a bing word.', function() {
         testEvent.event.content.body = "I really like coffee";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
     it('should bing on case-insensitive bing words.', function() {
         testEvent.event.content.body = "Coffee is great";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
     it('should bing on wildcard (.*) bing words.', function() {
         testEvent.event.content.body = "It was foomahbar I think.";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
@@ -280,7 +280,7 @@ describe('NotificationService', function() {
 
     it('should bing on character range ([a-z]) bing words.', function() {
         testEvent.event.content.body = "I ate 6 pies";
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(true);
     });
 
@@ -297,7 +297,7 @@ describe('NotificationService', function() {
 
     it('should gracefully handle bad input.', function() {
         testEvent.event.content.body = { "foo": "bar" };
-        let actions = pushProcessor.actionsForEvent(testEvent);
+        const actions = pushProcessor.actionsForEvent(testEvent);
         expect(actions.tweaks.highlight).toEqual(false);
     });
 });
diff --git a/spec/unit/realtime-callbacks.spec.js b/spec/unit/realtime-callbacks.spec.js
index a44d6a6dc..92ed513db 100644
--- a/spec/unit/realtime-callbacks.spec.js
+++ b/spec/unit/realtime-callbacks.spec.js
@@ -1,10 +1,10 @@
 "use strict";
 
-let callbacks = require("../../lib/realtime-callbacks");
-let testUtils = require("../test-utils.js");
+const callbacks = require("../../lib/realtime-callbacks");
+const testUtils = require("../test-utils.js");
 
 describe("realtime-callbacks", function() {
-    let clock = jasmine.Clock;
+    const clock = jasmine.Clock;
     let fakeDate;
 
     function tick(millis) {
@@ -28,7 +28,7 @@ describe("realtime-callbacks", function() {
 
     describe("setTimeout", function() {
         it("should call the callback after the timeout", function() {
-            let callback = jasmine.createSpy();
+            const callback = jasmine.createSpy();
             callbacks.setTimeout(callback, 100);
 
             expect(callback).not.toHaveBeenCalled();
@@ -38,7 +38,7 @@ describe("realtime-callbacks", function() {
 
 
         it("should default to a zero timeout", function() {
-            let callback = jasmine.createSpy();
+            const callback = jasmine.createSpy();
             callbacks.setTimeout(callback);
 
             expect(callback).not.toHaveBeenCalled();
@@ -47,14 +47,14 @@ describe("realtime-callbacks", function() {
         });
 
         it("should pass any parameters to the callback", function() {
-            let callback = jasmine.createSpy();
+            const callback = jasmine.createSpy();
             callbacks.setTimeout(callback, 0, "a", "b", "c");
             tick(0);
             expect(callback).toHaveBeenCalledWith("a", "b", "c");
         });
 
         it("should set 'this' to the global object", function() {
-            let callback = jasmine.createSpy();
+            const callback = jasmine.createSpy();
             callback.andCallFake(function() {
                 expect(this).toBe(global); // eslint-disable-line no-invalid-this
                 expect(this.console).toBeDefined(); // eslint-disable-line no-invalid-this
@@ -65,7 +65,7 @@ describe("realtime-callbacks", function() {
         });
 
         it("should handle timeouts of several seconds", function() {
-            let callback = jasmine.createSpy();
+            const callback = jasmine.createSpy();
             callbacks.setTimeout(callback, 2000);
 
             expect(callback).not.toHaveBeenCalled();
@@ -76,9 +76,9 @@ describe("realtime-callbacks", function() {
         });
 
         it("should call multiple callbacks in the right order", function() {
-            let callback1 = jasmine.createSpy("callback1");
-            let callback2 = jasmine.createSpy("callback2");
-            let callback3 = jasmine.createSpy("callback3");
+            const callback1 = jasmine.createSpy("callback1");
+            const callback2 = jasmine.createSpy("callback2");
+            const callback3 = jasmine.createSpy("callback3");
             callbacks.setTimeout(callback2, 200);
             callbacks.setTimeout(callback1, 100);
             callbacks.setTimeout(callback3, 300);
@@ -101,8 +101,8 @@ describe("realtime-callbacks", function() {
         });
 
         it("should treat -ve timeouts the same as a zero timeout", function() {
-            let callback1 = jasmine.createSpy("callback1");
-            let callback2 = jasmine.createSpy("callback2");
+            const callback1 = jasmine.createSpy("callback1");
+            const callback2 = jasmine.createSpy("callback2");
 
             // check that cb1 is called before cb2
             callback1.andCallFake(function() {
@@ -120,8 +120,8 @@ describe("realtime-callbacks", function() {
         });
 
         it("should not get confused by chained calls", function() {
-            let callback2 = jasmine.createSpy("callback2");
-            let callback1 = jasmine.createSpy("callback1");
+            const callback2 = jasmine.createSpy("callback2");
+            const callback1 = jasmine.createSpy("callback1");
             callback1.andCallFake(function() {
                 callbacks.setTimeout(callback2, 0);
                 expect(callback2).not.toHaveBeenCalled();
@@ -136,11 +136,11 @@ describe("realtime-callbacks", function() {
         });
 
         it("should be immune to exceptions", function() {
-            let callback1 = jasmine.createSpy("callback1");
+            const callback1 = jasmine.createSpy("callback1");
             callback1.andCallFake(function() {
                 throw new Error("prepare to die");
             });
-            let callback2 = jasmine.createSpy("callback2");
+            const callback2 = jasmine.createSpy("callback2");
             callbacks.setTimeout(callback1, 0);
             callbacks.setTimeout(callback2, 0);
 
@@ -154,19 +154,19 @@ describe("realtime-callbacks", function() {
 
     describe("cancelTimeout", function() {
         it("should cancel a pending timeout", function() {
-            let callback = jasmine.createSpy();
-            let k = callbacks.setTimeout(callback);
+            const callback = jasmine.createSpy();
+            const k = callbacks.setTimeout(callback);
             callbacks.clearTimeout(k);
             tick(0);
             expect(callback).not.toHaveBeenCalled();
         });
 
         it("should not affect sooner timeouts", function() {
-            let callback1 = jasmine.createSpy("callback1");
-            let callback2 = jasmine.createSpy("callback2");
+            const callback1 = jasmine.createSpy("callback1");
+            const callback2 = jasmine.createSpy("callback2");
 
             callbacks.setTimeout(callback1, 100);
-            let k = callbacks.setTimeout(callback2, 200);
+            const k = callbacks.setTimeout(callback2, 200);
             callbacks.clearTimeout(k);
 
             tick(100);
diff --git a/spec/unit/room-member.spec.js b/spec/unit/room-member.spec.js
index 6cd3ab109..04622c6ab 100644
--- a/spec/unit/room-member.spec.js
+++ b/spec/unit/room-member.spec.js
@@ -1,13 +1,13 @@
 "use strict";
-let sdk = require("../..");
-let RoomMember = sdk.RoomMember;
-let utils = require("../test-utils");
+const sdk = require("../..");
+const RoomMember = sdk.RoomMember;
+const utils = require("../test-utils");
 
 describe("RoomMember", function() {
-    let roomId = "!foo:bar";
-    let userA = "@alice:bar";
-    let userB = "@bertha:bar";
-    let userC = "@clarissa:bar";
+    const roomId = "!foo:bar";
+    const userA = "@alice:bar";
+    const userB = "@bertha:bar";
+    const userC = "@clarissa:bar";
     let member;
 
     beforeEach(function() {
@@ -16,7 +16,7 @@ describe("RoomMember", function() {
     });
 
     describe("getAvatarUrl", function() {
-        let hsUrl = "https://my.home.server";
+        const hsUrl = "https://my.home.server";
 
         it("should return the URL from m.room.member preferentially", function() {
             member.events.member = utils.mkEvent({
@@ -30,7 +30,7 @@ describe("RoomMember", function() {
                     avatar_url: "mxc://flibble/wibble",
                 },
             });
-            let url = member.getAvatarUrl(hsUrl);
+            const url = member.getAvatarUrl(hsUrl);
             // we don't care about how the mxc->http conversion is done, other
             // than it contains the mxc body.
             expect(url.indexOf("flibble/wibble")).not.toEqual(-1);
@@ -38,20 +38,20 @@ describe("RoomMember", function() {
 
         it("should return an identicon HTTP URL if allowDefault was set and there " +
         "was no m.room.member event", function() {
-            let url = member.getAvatarUrl(hsUrl, 64, 64, "crop", true);
+            const url = member.getAvatarUrl(hsUrl, 64, 64, "crop", true);
             expect(url.indexOf("http")).toEqual(0); // don't care about form
         });
 
         it("should return nothing if there is no m.room.member and allowDefault=false",
         function() {
-            let url = member.getAvatarUrl(hsUrl, 64, 64, "crop", false);
+            const url = member.getAvatarUrl(hsUrl, 64, 64, "crop", false);
             expect(url).toEqual(null);
         });
     });
 
     describe("setPowerLevelEvent", function() {
         it("should set 'powerLevel' and 'powerLevelNorm'.", function() {
-            let event = utils.mkEvent({
+            const event = utils.mkEvent({
                 type: "m.room.power_levels",
                 room: roomId,
                 user: userA,
@@ -68,7 +68,7 @@ describe("RoomMember", function() {
             expect(member.powerLevel).toEqual(20);
             expect(member.powerLevelNorm).toEqual(10);
 
-            let memberB = new RoomMember(roomId, userB);
+            const memberB = new RoomMember(roomId, userB);
             memberB.setPowerLevelEvent(event);
             expect(memberB.powerLevel).toEqual(200);
             expect(memberB.powerLevelNorm).toEqual(100);
@@ -76,7 +76,7 @@ describe("RoomMember", function() {
 
         it("should emit 'RoomMember.powerLevel' if the power level changes.",
         function() {
-            let event = utils.mkEvent({
+            const event = utils.mkEvent({
                 type: "m.room.power_levels",
                 room: roomId,
                 user: userA,
@@ -105,7 +105,7 @@ describe("RoomMember", function() {
 
         it("should honour power levels of zero.",
         function() {
-            let event = utils.mkEvent({
+            const event = utils.mkEvent({
                 type: "m.room.power_levels",
                 room: roomId,
                 user: userA,
@@ -138,12 +138,12 @@ describe("RoomMember", function() {
     describe("setTypingEvent", function() {
         it("should set 'typing'", function() {
             member.typing = false;
-            let memberB = new RoomMember(roomId, userB);
+            const memberB = new RoomMember(roomId, userB);
             memberB.typing = true;
-            let memberC = new RoomMember(roomId, userC);
+            const memberC = new RoomMember(roomId, userC);
             memberC.typing = true;
 
-            let event = utils.mkEvent({
+            const event = utils.mkEvent({
                 type: "m.typing",
                 user: userA,
                 room: roomId,
@@ -165,7 +165,7 @@ describe("RoomMember", function() {
 
         it("should emit 'RoomMember.typing' if the typing state changes",
         function() {
-            let event = utils.mkEvent({
+            const event = utils.mkEvent({
                 type: "m.typing",
                 room: roomId,
                 content: {
@@ -190,7 +190,7 @@ describe("RoomMember", function() {
     });
 
     describe("setMembershipEvent", function() {
-        let joinEvent = utils.mkMembership({
+        const joinEvent = utils.mkMembership({
             event: true,
             mship: "join",
             user: userA,
@@ -198,7 +198,7 @@ describe("RoomMember", function() {
             name: "Alice",
         });
 
-        let inviteEvent = utils.mkMembership({
+        const inviteEvent = utils.mkMembership({
             event: true,
             mship: "invite",
             user: userB,
@@ -218,7 +218,7 @@ describe("RoomMember", function() {
 
         it("should set 'name' based on user_id, displayname and room state",
         function() {
-            let roomState = {
+            const roomState = {
                 getStateEvents: function(type) {
                     if (type !== "m.room.member") {
                         return [];
diff --git a/spec/unit/room-state.spec.js b/spec/unit/room-state.spec.js
index 20903785a..eb2fb0595 100644
--- a/spec/unit/room-state.spec.js
+++ b/spec/unit/room-state.spec.js
@@ -1,13 +1,13 @@
 "use strict";
-let sdk = require("../..");
-let RoomState = sdk.RoomState;
-let RoomMember = sdk.RoomMember;
-let utils = require("../test-utils");
+const sdk = require("../..");
+const RoomState = sdk.RoomState;
+const RoomMember = sdk.RoomMember;
+const utils = require("../test-utils");
 
 describe("RoomState", function() {
-    let roomId = "!foo:bar";
-    let userA = "@alice:bar";
-    let userB = "@bob:bar";
+    const roomId = "!foo:bar";
+    const userA = "@alice:bar";
+    const userB = "@bob:bar";
     let state;
 
     beforeEach(function() {
@@ -40,7 +40,7 @@ describe("RoomState", function() {
         });
 
         it("should return a member for each m.room.member event", function() {
-            let members = state.getMembers();
+            const members = state.getMembers();
             expect(members.length).toEqual(2);
             // ordering unimportant
             expect([userA, userB].indexOf(members[0].userId)).not.toEqual(-1);
@@ -58,7 +58,7 @@ describe("RoomState", function() {
         });
 
         it("should return a member which changes as state changes", function() {
-            let member = state.getMember(userB);
+            const member = state.getMember(userB);
             expect(member.membership).toEqual("join");
             expect(member.name).toEqual(userB);
 
@@ -81,14 +81,14 @@ describe("RoomState", function() {
 
         it("should return a member which doesn't change when the state is updated",
         function() {
-            let preLeaveUser = state.getSentinelMember(userA);
+            const preLeaveUser = state.getSentinelMember(userA);
             state.setStateEvents([
                 utils.mkMembership({
                     room: roomId, user: userA, mship: "leave", event: true,
                     name: "AliceIsGone",
                 }),
             ]);
-            let postLeaveUser = state.getSentinelMember(userA);
+            const postLeaveUser = state.getSentinelMember(userA);
 
             expect(preLeaveUser.membership).toEqual("join");
             expect(preLeaveUser.name).toEqual(userA);
@@ -111,7 +111,7 @@ describe("RoomState", function() {
 
         it("should return a list of matching events if no state_key was specified",
         function() {
-            let events = state.getStateEvents("m.room.member");
+            const events = state.getStateEvents("m.room.member");
             expect(events.length).toEqual(2);
             // ordering unimportant
             expect([userA, userB].indexOf(events[0].getStateKey())).not.toEqual(-1);
@@ -120,7 +120,7 @@ describe("RoomState", function() {
 
         it("should return a single MatrixEvent if a state_key was specified",
         function() {
-            let event = state.getStateEvents("m.room.member", userA);
+            const event = state.getStateEvents("m.room.member", userA);
             expect(event.getContent()).toEqual({
                 membership: "join",
             });
@@ -129,7 +129,7 @@ describe("RoomState", function() {
 
     describe("setStateEvents", function() {
         it("should emit 'RoomState.members' for each m.room.member event", function() {
-            let memberEvents = [
+            const memberEvents = [
                 utils.mkMembership({
                     user: "@cleo:bar", mship: "invite", room: roomId, event: true,
                 }),
@@ -149,7 +149,7 @@ describe("RoomState", function() {
         });
 
         it("should emit 'RoomState.newMember' for each new member added", function() {
-            let memberEvents = [
+            const memberEvents = [
                 utils.mkMembership({
                     user: "@cleo:bar", mship: "invite", room: roomId, event: true,
                 }),
@@ -168,7 +168,7 @@ describe("RoomState", function() {
         });
 
         it("should emit 'RoomState.events' for each state event", function() {
-            let events = [
+            const events = [
                 utils.mkMembership({
                     user: "@cleo:bar", mship: "invite", room: roomId, event: true,
                 }),
@@ -198,7 +198,7 @@ describe("RoomState", function() {
             state.members[userA] = utils.mock(RoomMember);
             state.members[userB] = utils.mock(RoomMember);
 
-            let powerLevelEvent = utils.mkEvent({
+            const powerLevelEvent = utils.mkEvent({
                 type: "m.room.power_levels", room: roomId, user: userA, event: true,
                 content: {
                     users_default: 10,
@@ -219,11 +219,11 @@ describe("RoomState", function() {
 
         it("should call setPowerLevelEvent on a new RoomMember if power levels exist",
         function() {
-            let userC = "@cleo:bar";
-            let memberEvent = utils.mkMembership({
+            const userC = "@cleo:bar";
+            const memberEvent = utils.mkMembership({
                 mship: "join", user: userC, room: roomId, event: true,
             });
-            let powerLevelEvent = utils.mkEvent({
+            const powerLevelEvent = utils.mkEvent({
                 type: "m.room.power_levels", room: roomId, user: userA, event: true,
                 content: {
                     users_default: 10,
@@ -247,7 +247,7 @@ describe("RoomState", function() {
             state.members[userA] = utils.mock(RoomMember);
             state.members[userB] = utils.mock(RoomMember);
 
-            let memberEvent = utils.mkMembership({
+            const memberEvent = utils.mkMembership({
                 user: userB, mship: "leave", room: roomId, event: true,
             });
             state.setStateEvents([memberEvent]);
@@ -261,7 +261,7 @@ describe("RoomState", function() {
 
     describe("setTypingEvent", function() {
         it("should call setTypingEvent on each RoomMember", function() {
-            let typingEvent = utils.mkEvent({
+            const typingEvent = utils.mkEvent({
                 type: "m.typing", room: roomId, event: true, content: {
                     user_ids: [userA],
                 },
@@ -296,7 +296,7 @@ describe("RoomState", function() {
         it("should say members with power >=50 may send state with power level event " +
         "but no state default",
         function() {
-            let powerLevelEvent = {
+            const powerLevelEvent = {
                 type: "m.room.power_levels", room: roomId, user: userA, event: true,
                 content: {
                     users_default: 10,
@@ -316,7 +316,7 @@ describe("RoomState", function() {
 
         it("should obey state_default",
         function() {
-            let powerLevelEvent = {
+            const powerLevelEvent = {
                 type: "m.room.power_levels", room: roomId, user: userA, event: true,
                 content: {
                     users_default: 10,
@@ -337,7 +337,7 @@ describe("RoomState", function() {
 
         it("should honour explicit event power levels in the power_levels event",
         function() {
-            let powerLevelEvent = {
+            const powerLevelEvent = {
                 type: "m.room.power_levels", room: roomId, user: userA, event: true,
                 content: {
                     events: {
@@ -380,7 +380,7 @@ describe("RoomState", function() {
 
         it("should obey events_default",
         function() {
-            let powerLevelEvent = {
+            const powerLevelEvent = {
                 type: "m.room.power_levels", room: roomId, user: userA, event: true,
                 content: {
                     users_default: 10,
@@ -404,7 +404,7 @@ describe("RoomState", function() {
 
         it("should honour explicit event power levels in the power_levels event",
         function() {
-            let powerLevelEvent = {
+            const powerLevelEvent = {
                 type: "m.room.power_levels", room: roomId, user: userA, event: true,
                 content: {
                     events: {
diff --git a/spec/unit/room.spec.js b/spec/unit/room.spec.js
index 599dbbc2a..8c1999c46 100644
--- a/spec/unit/room.spec.js
+++ b/spec/unit/room.spec.js
@@ -1,18 +1,18 @@
 "use strict";
-let sdk = require("../..");
-let Room = sdk.Room;
-let RoomState = sdk.RoomState;
-let MatrixEvent = sdk.MatrixEvent;
-let EventStatus = sdk.EventStatus;
-let EventTimeline = sdk.EventTimeline;
-let utils = require("../test-utils");
+const sdk = require("../..");
+const Room = sdk.Room;
+const RoomState = sdk.RoomState;
+const MatrixEvent = sdk.MatrixEvent;
+const EventStatus = sdk.EventStatus;
+const EventTimeline = sdk.EventTimeline;
+const utils = require("../test-utils");
 
 describe("Room", function() {
-    let roomId = "!foo:bar";
-    let userA = "@alice:bar";
-    let userB = "@bertha:bar";
-    let userC = "@clarissa:bar";
-    let userD = "@dorothy:bar";
+    const roomId = "!foo:bar";
+    const userA = "@alice:bar";
+    const userB = "@bertha:bar";
+    const userC = "@clarissa:bar";
+    const userD = "@dorothy:bar";
     let room;
 
     beforeEach(function() {
@@ -26,7 +26,7 @@ describe("Room", function() {
     });
 
     describe("getAvatarUrl", function() {
-        let hsUrl = "https://my.home.server";
+        const hsUrl = "https://my.home.server";
 
         it("should return the URL from m.room.avatar preferentially", function() {
             room.currentState.getStateEvents.andCallFake(function(type, key) {
@@ -43,7 +43,7 @@ describe("Room", function() {
                     });
                 }
             });
-            let url = room.getAvatarUrl(hsUrl);
+            const url = room.getAvatarUrl(hsUrl);
             // we don't care about how the mxc->http conversion is done, other
             // than it contains the mxc body.
             expect(url.indexOf("flibble/wibble")).not.toEqual(-1);
@@ -51,13 +51,13 @@ describe("Room", function() {
 
         it("should return an identicon HTTP URL if allowDefault was set and there " +
         "was no m.room.avatar event", function() {
-            let url = room.getAvatarUrl(hsUrl, 64, 64, "crop", true);
+            const url = room.getAvatarUrl(hsUrl, 64, 64, "crop", true);
             expect(url.indexOf("http")).toEqual(0); // don't care about form
         });
 
         it("should return nothing if there is no m.room.avatar and allowDefault=false",
         function() {
-            let url = room.getAvatarUrl(hsUrl, 64, 64, "crop", false);
+            const url = room.getAvatarUrl(hsUrl, 64, 64, "crop", false);
             expect(url).toEqual(null);
         });
     });
@@ -83,7 +83,7 @@ describe("Room", function() {
     });
 
     describe("addLiveEvents", function() {
-        let events = [
+        const events = [
             utils.mkMessage({
                 room: roomId, user: userA, msg: "changing room name", event: true,
             }),
@@ -95,7 +95,7 @@ describe("Room", function() {
 
         it("should call RoomState.setTypingEvent on m.typing events", function() {
             room.currentState = utils.mock(RoomState);
-            let typing = utils.mkEvent({
+            const typing = utils.mkEvent({
                 room: roomId, type: "m.typing", event: true, content: {
                     user_ids: [userA],
                 },
@@ -112,7 +112,7 @@ describe("Room", function() {
 
         it("should replace a timeline event if dupe strategy is 'replace'", function() {
             // make a duplicate
-            let dupe = utils.mkMessage({
+            const dupe = utils.mkMessage({
                 room: roomId, user: userA, msg: "dupe", event: true,
             });
             dupe.event.event_id = events[0].getId();
@@ -124,7 +124,7 @@ describe("Room", function() {
 
         it("should ignore a given dupe event if dupe strategy is 'ignore'", function() {
             // make a duplicate
-            let dupe = utils.mkMessage({
+            const dupe = utils.mkMessage({
                 room: roomId, user: userA, msg: "dupe", event: true,
             });
             dupe.event.event_id = events[0].getId();
@@ -150,7 +150,7 @@ describe("Room", function() {
 
         it("should call setStateEvents on the right RoomState with the right " +
         "forwardLooking value for new events", function() {
-            let events = [
+            const events = [
                 utils.mkMembership({
                     room: roomId, mship: "invite", user: userB, skey: userA, event: true,
                 }),
@@ -174,7 +174,7 @@ describe("Room", function() {
         });
 
         it("should synthesize read receipts for the senders of events", function() {
-            let sentinel = {
+            const sentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Alice",
@@ -190,17 +190,17 @@ describe("Room", function() {
         });
 
         it("should emit Room.localEchoUpdated when a local echo is updated", function() {
-            let localEvent = utils.mkMessage({
+            const localEvent = utils.mkMessage({
                 room: roomId, user: userA, event: true,
             });
             localEvent.status = EventStatus.SENDING;
-            let localEventId = localEvent.getId();
+            const localEventId = localEvent.getId();
 
-            let remoteEvent = utils.mkMessage({
+            const remoteEvent = utils.mkMessage({
                 room: roomId, user: userA, event: true,
             });
             remoteEvent.event.unsigned = {transaction_id: "TXN_ID"};
-            let remoteEventId = remoteEvent.getId();
+            const remoteEventId = remoteEvent.getId();
 
             let callCount = 0;
             room.on("Room.localEchoUpdated",
@@ -238,7 +238,7 @@ describe("Room", function() {
     });
 
     describe("addEventsToTimeline", function() {
-        let events = [
+        const events = [
             utils.mkMessage({
                 room: roomId, user: userA, msg: "changing room name", event: true,
             }),
@@ -278,12 +278,12 @@ describe("Room", function() {
 
     describe("event metadata handling", function() {
         it("should set event.sender for new and old events", function() {
-            let sentinel = {
+            const sentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Alice",
             };
-            let oldSentinel = {
+            const oldSentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Old Alice",
@@ -301,11 +301,11 @@ describe("Room", function() {
                 return null;
             });
 
-            let newEv = utils.mkEvent({
+            const newEv = utils.mkEvent({
                 type: "m.room.name", room: roomId, user: userA, event: true,
                 content: { name: "New Room Name" },
             });
-            let oldEv = utils.mkEvent({
+            const oldEv = utils.mkEvent({
                 type: "m.room.name", room: roomId, user: userA, event: true,
                 content: { name: "Old Room Name" },
             });
@@ -317,12 +317,12 @@ describe("Room", function() {
 
         it("should set event.target for new and old m.room.member events",
         function() {
-            let sentinel = {
+            const sentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Alice",
             };
-            let oldSentinel = {
+            const oldSentinel = {
                 userId: userA,
                 membership: "join",
                 name: "Old Alice",
@@ -340,10 +340,10 @@ describe("Room", function() {
                 return null;
             });
 
-            let newEv = utils.mkMembership({
+            const newEv = utils.mkMembership({
                 room: roomId, mship: "invite", user: userB, skey: userA, event: true,
             });
-            let oldEv = utils.mkMembership({
+            const oldEv = utils.mkMembership({
                 room: roomId, mship: "ban", user: userB, skey: userA, event: true,
             });
             room.addLiveEvents([newEv]);
@@ -354,7 +354,7 @@ describe("Room", function() {
 
         it("should call setStateEvents on the right RoomState with the right " +
         "forwardLooking value for old events", function() {
-            let events = [
+            const events = [
                 utils.mkMembership({
                     room: roomId, mship: "invite", user: userB, skey: userA, event: true,
                 }),
@@ -379,8 +379,8 @@ describe("Room", function() {
         });
     });
 
-    let resetTimelineTests = function(timelineSupport) {
-        let events = [
+    const resetTimelineTests = function(timelineSupport) {
+        const events = [
             utils.mkMessage({
                 room: roomId, user: userA, msg: "A message", event: true,
             }),
@@ -404,8 +404,8 @@ describe("Room", function() {
             room.resetLiveTimeline();
 
             room.addLiveEvents([events[2]]);
-            let oldState = room.getLiveTimeline().getState(EventTimeline.BACKWARDS);
-            let newState = room.getLiveTimeline().getState(EventTimeline.FORWARDS);
+            const oldState = room.getLiveTimeline().getState(EventTimeline.BACKWARDS);
+            const newState = room.getLiveTimeline().getState(EventTimeline.FORWARDS);
             expect(room.getLiveTimeline().getEvents().length).toEqual(1);
             expect(oldState.getStateEvents("m.room.name", "")).toEqual(events[1]);
             expect(newState.getStateEvents("m.room.name", "")).toEqual(events[2]);
@@ -417,7 +417,7 @@ describe("Room", function() {
             room.resetLiveTimeline();
 
             room.addLiveEvents([events[2]]);
-            let newLiveTimeline = room.getLiveTimeline();
+            const newLiveTimeline = room.getLiveTimeline();
             expect(room.timeline).toEqual(newLiveTimeline.getEvents());
             expect(room.oldState).toEqual(
                 newLiveTimeline.getState(EventTimeline.BACKWARDS));
@@ -434,7 +434,7 @@ describe("Room", function() {
 
                 // make sure that the pagination token has been set before the
                 // event is emitted.
-                let tok = emitRoom.getLiveTimeline()
+                const tok = emitRoom.getLiveTimeline()
                     .getPaginationToken(EventTimeline.BACKWARDS);
 
                 expect(tok).toEqual("pagToken");
@@ -447,10 +447,10 @@ describe("Room", function() {
                 " old timelines", function() {
             room.addLiveEvents([events[0]]);
             expect(room.timeline.length).toEqual(1);
-            let firstLiveTimeline = room.getLiveTimeline();
+            const firstLiveTimeline = room.getLiveTimeline();
             room.resetLiveTimeline();
 
-            let tl = room.getTimelineForEvent(events[0].getId());
+            const tl = room.getTimelineForEvent(events[0].getId());
             expect(tl).toBe(timelineSupport ? firstLiveTimeline : null);
         });
     };
@@ -465,7 +465,7 @@ describe("Room", function() {
             room = new Room(roomId, {timelineSupport: true});
         });
 
-        let events = [
+        const events = [
             utils.mkMessage({
                 room: roomId, user: userA, msg: "1111", event: true,
             }),
@@ -492,7 +492,7 @@ describe("Room", function() {
         });
 
         it("should handle events in adjacent timelines", function() {
-            let oldTimeline = room.addTimeline();
+            const oldTimeline = room.addTimeline();
             oldTimeline.setNeighbouringTimeline(room.getLiveTimeline(), 'f');
             room.getLiveTimeline().setNeighbouringTimeline(oldTimeline, 'b');
 
@@ -508,7 +508,7 @@ describe("Room", function() {
         });
 
         it("should return null for events in non-adjacent timelines", function() {
-            let oldTimeline = room.addTimeline();
+            const oldTimeline = room.addTimeline();
 
             room.addEventsToTimeline([events[0]], false, oldTimeline);
             room.addLiveEvents([events[1]]);
@@ -545,7 +545,7 @@ describe("Room", function() {
                     { userId: "@cleo:bar", membership: "leave" },
                 ];
             });
-            let res = room.getJoinedMembers();
+            const res = room.getJoinedMembers();
             expect(res.length).toEqual(1);
             expect(res[0].userId).toEqual("@alice:bar");
         });
@@ -556,7 +556,7 @@ describe("Room", function() {
                     { userId: "@bob:bar", membership: "invite" },
                 ];
             });
-            let res = room.getJoinedMembers();
+            const res = room.getJoinedMembers();
             expect(res.length).toEqual(0);
         });
     });
@@ -607,14 +607,14 @@ describe("Room", function() {
             // event.type + "$" event.state_key : MatrixEvent
         };
 
-        let setJoinRule = function(rule) {
+        const setJoinRule = function(rule) {
             stateLookup["m.room.join_rules$"] = utils.mkEvent({
                 type: "m.room.join_rules", room: roomId, user: userA, content: {
                     join_rule: rule,
                 }, event: true,
             });
         };
-        let setAliases = function(aliases, stateKey) {
+        const setAliases = function(aliases, stateKey) {
             if (!stateKey) {
                 stateKey = "flibble";
             }
@@ -624,14 +624,14 @@ describe("Room", function() {
                 }, event: true,
             });
         };
-        let setRoomName = function(name) {
+        const setRoomName = function(name) {
             stateLookup["m.room.name$"] = utils.mkEvent({
                 type: "m.room.name", room: roomId, user: userA, content: {
                     name: name,
                 }, event: true,
             });
         };
-        let addMember = function(userId, state, opts) {
+        const addMember = function(userId, state, opts) {
             if (!state) {
                 state = "join";
             }
@@ -648,9 +648,9 @@ describe("Room", function() {
             stateLookup = {};
             room.currentState.getStateEvents.andCallFake(function(type, key) {
                 if (key === undefined) {
-                    let prefix = type + "$";
-                    let list = [];
-                    for (let stateBlob in stateLookup) {
+                    const prefix = type + "$";
+                    const list = [];
+                    for (const stateBlob in stateLookup) {
                         if (!stateLookup.hasOwnProperty(stateBlob)) {
                             continue;
                         }
@@ -664,8 +664,8 @@ describe("Room", function() {
                 }
             });
             room.currentState.getMembers.andCallFake(function() {
-                let memberEvents = room.currentState.getStateEvents("m.room.member");
-                let members = [];
+                const memberEvents = room.currentState.getStateEvents("m.room.member");
+                const members = [];
                 for (let i = 0; i < memberEvents.length; i++) {
                     members.push({
                         name: memberEvents[i].event.content &&
@@ -679,7 +679,7 @@ describe("Room", function() {
                 return members;
             });
             room.currentState.getMember.andCallFake(function(userId) {
-                let memberEvent = room.currentState.getStateEvents(
+                const memberEvent = room.currentState.getStateEvents(
                     "m.room.member", userId
                 );
                 return {
@@ -696,7 +696,7 @@ describe("Room", function() {
         describe("Room.recalculate => Stripped State Events", function() {
             it("should set stripped state events as actual state events if the " +
             "room is an invite room", function() {
-                let roomName = "flibble";
+                const roomName = "flibble";
 
                 addMember(userA, "invite");
                 stateLookup["m.room.member$" + userA].event.invite_room_state = [
@@ -712,7 +712,7 @@ describe("Room", function() {
                 room.recalculate(userA);
                 expect(room.currentState.setStateEvents).toHaveBeenCalled();
                 // first call, first arg (which is an array), first element in array
-                let fakeEvent = room.currentState.setStateEvents.calls[0].args[0][0];
+                const fakeEvent = room.currentState.setStateEvents.calls[0].args[0][0];
                 expect(fakeEvent.getContent()).toEqual({
                     name: roomName,
                 });
@@ -745,9 +745,9 @@ describe("Room", function() {
                 addMember(userC);
                 addMember(userD);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 // we expect at least 1 member to be mentioned
-                let others = [userB, userC, userD];
+                const others = [userB, userC, userD];
                 let found = false;
                 for (let i = 0; i < others.length; i++) {
                     if (name.indexOf(others[i]) !== -1) {
@@ -766,7 +766,7 @@ describe("Room", function() {
                 addMember(userB);
                 addMember(userC);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name.indexOf(userB)).not.toEqual(-1, name);
                 expect(name.indexOf(userC)).not.toEqual(-1, name);
             });
@@ -779,7 +779,7 @@ describe("Room", function() {
                 addMember(userB);
                 addMember(userC);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name.indexOf(userB)).not.toEqual(-1, name);
                 expect(name.indexOf(userC)).not.toEqual(-1, name);
             });
@@ -791,7 +791,7 @@ describe("Room", function() {
                 addMember(userA);
                 addMember(userB);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name.indexOf(userB)).not.toEqual(-1, name);
             });
 
@@ -802,7 +802,7 @@ describe("Room", function() {
                 addMember(userA);
                 addMember(userB);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name.indexOf(userB)).not.toEqual(-1, name);
             });
 
@@ -812,47 +812,47 @@ describe("Room", function() {
                 addMember(userA, "invite", {user: userB});
                 addMember(userB);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name.indexOf(userB)).not.toEqual(-1, name);
             });
 
             it("should show the room alias if one exists for private " +
             "(invite join_rules) rooms if a room name doesn't exist.", function() {
-                let alias = "#room_alias:here";
+                const alias = "#room_alias:here";
                 setJoinRule("invite");
                 setAliases([alias, "#another:one"]);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual(alias);
             });
 
             it("should show the room alias if one exists for public " +
             "(public join_rules) rooms if a room name doesn't exist.", function() {
-                let alias = "#room_alias:here";
+                const alias = "#room_alias:here";
                 setJoinRule("public");
                 setAliases([alias, "#another:one"]);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual(alias);
             });
 
             it("should show the room name if one exists for private " +
             "(invite join_rules) rooms.", function() {
-                let roomName = "A mighty name indeed";
+                const roomName = "A mighty name indeed";
                 setJoinRule("invite");
                 setRoomName(roomName);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual(roomName);
             });
 
             it("should show the room name if one exists for public " +
             "(public join_rules) rooms.", function() {
-                let roomName = "A mighty name indeed";
+                const roomName = "A mighty name indeed";
                 setJoinRule("public");
                 setRoomName(roomName);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual(roomName);
             });
 
@@ -861,7 +861,7 @@ describe("Room", function() {
                 setJoinRule("invite");
                 addMember(userA);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual("Empty room");
             });
 
@@ -870,7 +870,7 @@ describe("Room", function() {
                 setJoinRule("public");
                 addMember(userA);
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual("Empty room");
             });
 
@@ -878,7 +878,7 @@ describe("Room", function() {
                "alias or members in the room.",
             function() {
                 room.recalculate(userA);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual("Empty room");
             });
 
@@ -889,7 +889,7 @@ describe("Room", function() {
                 addMember(userA, 'join', {name: "Alice"});
                 addMember(userB, "invite", {user: userA});
                 room.recalculate(userB);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual("Invite from Alice");
             });
 
@@ -899,20 +899,20 @@ describe("Room", function() {
                 addMember(userA);
                 addMember(userB, "invite", {user: userA});
                 room.recalculate(userB);
-                let name = room.name;
+                const name = room.name;
                 expect(name).toEqual("Invite from " + userA);
             });
         });
     });
 
     describe("receipts", function() {
-        let eventToAck = utils.mkMessage({
+        const eventToAck = utils.mkMessage({
             room: roomId, user: userA, msg: "PLEASE ACKNOWLEDGE MY EXISTENCE",
             event: true,
         });
 
         function mkReceipt(roomId, records) {
-            let content = {};
+            const content = {};
             records.forEach(function(r) {
                 if (!content[r.eventId]) {
                     content[r.eventId] = {};
@@ -944,7 +944,7 @@ describe("Room", function() {
         describe("addReceipt", function() {
             it("should store the receipt so it can be obtained via getReceiptsForEvent",
             function() {
-                let ts = 13787898424;
+                const ts = 13787898424;
                 room.addReceipt(mkReceipt(roomId, [
                     mkRecord(eventToAck.getId(), "m.read", userB, ts),
                 ]));
@@ -959,12 +959,12 @@ describe("Room", function() {
 
             it("should emit an event when a receipt is added",
             function() {
-                let listener = jasmine.createSpy('spy');
+                const listener = jasmine.createSpy('spy');
                 room.on("Room.receipt", listener);
 
-                let ts = 13787898424;
+                const ts = 13787898424;
 
-                let receiptEvent = mkReceipt(roomId, [
+                const receiptEvent = mkReceipt(roomId, [
                     mkRecord(eventToAck.getId(), "m.read", userB, ts),
                 ]);
 
@@ -973,15 +973,15 @@ describe("Room", function() {
             });
 
             it("should clobber receipts based on type and user ID", function() {
-                let nextEventToAck = utils.mkMessage({
+                const nextEventToAck = utils.mkMessage({
                     room: roomId, user: userA, msg: "I AM HERE YOU KNOW",
                     event: true,
                 });
-                let ts = 13787898424;
+                const ts = 13787898424;
                 room.addReceipt(mkReceipt(roomId, [
                     mkRecord(eventToAck.getId(), "m.read", userB, ts),
                 ]));
-                let ts2 = 13787899999;
+                const ts2 = 13787899999;
                 room.addReceipt(mkReceipt(roomId, [
                     mkRecord(nextEventToAck.getId(), "m.read", userB, ts2),
                 ]));
@@ -996,7 +996,7 @@ describe("Room", function() {
             });
 
             it("should persist multiple receipts for a single event ID", function() {
-                let ts = 13787898424;
+                const ts = 13787898424;
                 room.addReceipt(mkReceipt(roomId, [
                     mkRecord(eventToAck.getId(), "m.read", userB, ts),
                     mkRecord(eventToAck.getId(), "m.read", userC, ts),
@@ -1008,15 +1008,15 @@ describe("Room", function() {
             });
 
             it("should persist multiple receipts for a single receipt type", function() {
-                let eventTwo = utils.mkMessage({
+                const eventTwo = utils.mkMessage({
                     room: roomId, user: userA, msg: "2222",
                     event: true,
                 });
-                let eventThree = utils.mkMessage({
+                const eventThree = utils.mkMessage({
                     room: roomId, user: userA, msg: "3333",
                     event: true,
                 });
-                let ts = 13787898424;
+                const ts = 13787898424;
                 room.addReceipt(mkReceipt(roomId, [
                     mkRecord(eventToAck.getId(), "m.read", userB, ts),
                     mkRecord(eventTwo.getId(), "m.read", userC, ts),
@@ -1059,7 +1059,7 @@ describe("Room", function() {
             });
 
             it("should prioritise the most recent event", function() {
-                let events = [
+                const events = [
                     utils.mkMessage({
                         room: roomId, user: userA, msg: "1111",
                         event: true,
@@ -1075,7 +1075,7 @@ describe("Room", function() {
                 ];
 
                 room.addLiveEvents(events);
-                let ts = 13787898424;
+                const ts = 13787898424;
 
                 // check it initialises correctly
                 room.addReceipt(mkReceipt(roomId, [
@@ -1099,7 +1099,7 @@ describe("Room", function() {
 
         describe("getUsersReadUpTo", function() {
             it("should return user IDs read up to the given event", function() {
-                let ts = 13787898424;
+                const ts = 13787898424;
                 room.addReceipt(mkReceipt(roomId, [
                     mkRecord(eventToAck.getId(), "m.read", userB, ts),
                 ]));
@@ -1110,7 +1110,7 @@ describe("Room", function() {
 
     describe("tags", function() {
         function mkTags(roomId, tags) {
-            let content = { "tags": tags };
+            const content = { "tags": tags };
             return new MatrixEvent({
                 content: content,
                 room_id: roomId,
@@ -1122,7 +1122,7 @@ describe("Room", function() {
             it("should set tags on rooms from event stream so " +
                "they can be obtained by the tags property",
             function() {
-                let tags = { "m.foo": { "order": 0.5 } };
+                const tags = { "m.foo": { "order": 0.5 } };
                 room.addTags(mkTags(roomId, tags));
                 expect(room.tags).toEqual(tags);
             });
@@ -1130,11 +1130,11 @@ describe("Room", function() {
             it("should emit Room.tags event when new tags are " +
                "received on the event stream",
             function() {
-                let listener = jasmine.createSpy('spy');
+                const listener = jasmine.createSpy('spy');
                 room.on("Room.tags", listener);
 
-                let tags = { "m.foo": { "order": 0.5 } };
-                let event = mkTags(roomId, tags);
+                const tags = { "m.foo": { "order": 0.5 } };
+                const event = mkTags(roomId, tags);
                 room.addTags(event);
                 expect(listener).toHaveBeenCalledWith(event, room);
             });
@@ -1147,17 +1147,17 @@ describe("Room", function() {
     describe("addPendingEvent", function() {
         it("should add pending events to the pendingEventList if " +
                       "pendingEventOrdering == 'detached'", function() {
-            let room = new Room(roomId, {
+            const room = new Room(roomId, {
                 pendingEventOrdering: "detached",
             });
-            let eventA = utils.mkMessage({
+            const eventA = utils.mkMessage({
                 room: roomId, user: userA, msg: "remote 1", event: true,
             });
-            let eventB = utils.mkMessage({
+            const eventB = utils.mkMessage({
                 room: roomId, user: userA, msg: "local 1", event: true,
             });
             eventB.status = EventStatus.SENDING;
-            let eventC = utils.mkMessage({
+            const eventC = utils.mkMessage({
                 room: roomId, user: userA, msg: "remote 2", event: true,
             });
             room.addLiveEvents([eventA]);
@@ -1176,14 +1176,14 @@ describe("Room", function() {
             room = new Room(roomId, {
                 pendingEventOrdering: "chronological",
             });
-            let eventA = utils.mkMessage({
+            const eventA = utils.mkMessage({
                 room: roomId, user: userA, msg: "remote 1", event: true,
             });
-            let eventB = utils.mkMessage({
+            const eventB = utils.mkMessage({
                 room: roomId, user: userA, msg: "local 1", event: true,
             });
             eventB.status = EventStatus.SENDING;
-            let eventC = utils.mkMessage({
+            const eventC = utils.mkMessage({
                 room: roomId, user: userA, msg: "remote 2", event: true,
             });
             room.addLiveEvents([eventA]);
@@ -1197,14 +1197,14 @@ describe("Room", function() {
 
     describe("updatePendingEvent", function() {
         it("should remove cancelled events from the pending list", function() {
-            let room = new Room(roomId, {
+            const room = new Room(roomId, {
                 pendingEventOrdering: "detached",
             });
-            let eventA = utils.mkMessage({
+            const eventA = utils.mkMessage({
                 room: roomId, user: userA, event: true,
             });
             eventA.status = EventStatus.SENDING;
-            let eventId = eventA.getId();
+            const eventId = eventA.getId();
 
             room.addPendingEvent(eventA, "TXN1");
             expect(room.getPendingEvents()).toEqual(
@@ -1233,12 +1233,12 @@ describe("Room", function() {
 
 
         it("should remove cancelled events from the timeline", function() {
-            let room = new Room(roomId);
-            let eventA = utils.mkMessage({
+            const room = new Room(roomId);
+            const eventA = utils.mkMessage({
                 room: roomId, user: userA, event: true,
             });
             eventA.status = EventStatus.SENDING;
-            let eventId = eventA.getId();
+            const eventId = eventA.getId();
 
             room.addPendingEvent(eventA, "TXN1");
             expect(room.getLiveTimeline().getEvents()).toEqual(
diff --git a/spec/unit/scheduler.spec.js b/spec/unit/scheduler.spec.js
index c2f4c6741..b6364dc02 100644
--- a/spec/unit/scheduler.spec.js
+++ b/spec/unit/scheduler.spec.js
@@ -1,22 +1,22 @@
 // This file had a function whose name is all caps, which displeases eslint
 /* eslint new-cap: "off" */
 
-let q = require("q");
-let sdk = require("../..");
-let MatrixScheduler = sdk.MatrixScheduler;
-let MatrixError = sdk.MatrixError;
-let utils = require("../test-utils");
+const q = require("q");
+const sdk = require("../..");
+const MatrixScheduler = sdk.MatrixScheduler;
+const MatrixError = sdk.MatrixError;
+const utils = require("../test-utils");
 
 describe("MatrixScheduler", function() {
     let scheduler;
     let retryFn;
     let queueFn;
     let defer;
-    let roomId = "!foo:bar";
-    let eventA = utils.mkMessage({
+    const roomId = "!foo:bar";
+    const eventA = utils.mkMessage({
         user: "@alice:bar", room: roomId, event: true,
     });
-    let eventB = utils.mkMessage({
+    const eventB = utils.mkMessage({
         user: "@alice:bar", room: roomId, event: true,
     });
 
@@ -46,8 +46,8 @@ describe("MatrixScheduler", function() {
         queueFn = function() {
             return "one_big_queue";
         };
-        let deferA = q.defer();
-        let deferB = q.defer();
+        const deferA = q.defer();
+        const deferB = q.defer();
         let resolvedA = false;
         scheduler.setProcessFunction(function(event) {
             if (resolvedA) {
@@ -70,8 +70,8 @@ describe("MatrixScheduler", function() {
 
     it("should invoke the retryFn on failure and wait the amount of time specified",
     function(done) {
-        let waitTimeMs = 1500;
-        let retryDefer = q.defer();
+        const waitTimeMs = 1500;
+        const retryDefer = q.defer();
         retryFn = function() {
             retryDefer.resolve();
             return waitTimeMs;
@@ -116,8 +116,8 @@ describe("MatrixScheduler", function() {
  return "yep";
 };
 
-        let deferA = q.defer();
-        let deferB = q.defer();
+        const deferA = q.defer();
+        const deferB = q.defer();
         let procCount = 0;
         scheduler.setProcessFunction(function(ev) {
             procCount += 1;
@@ -131,7 +131,7 @@ describe("MatrixScheduler", function() {
             expect(procCount).toBeLessThan(3);
         });
 
-        let globalA = scheduler.queueEvent(eventA);
+        const globalA = scheduler.queueEvent(eventA);
         scheduler.queueEvent(eventB);
 
         expect(procCount).toEqual(1);
@@ -149,10 +149,10 @@ describe("MatrixScheduler", function() {
         // Expect to have processFn invoked for A&B.
         // Resolve A.
         // Expect to have processFn invoked for D.
-        let eventC = utils.mkMessage({user: "@a:bar", room: roomId, event: true});
-        let eventD = utils.mkMessage({user: "@b:bar", room: roomId, event: true});
+        const eventC = utils.mkMessage({user: "@a:bar", room: roomId, event: true});
+        const eventD = utils.mkMessage({user: "@b:bar", room: roomId, event: true});
 
-        let buckets = {};
+        const buckets = {};
         buckets[eventA.getId()] = "queue_A";
         buckets[eventD.getId()] = "queue_A";
         buckets[eventB.getId()] = "queue_B";
@@ -165,12 +165,12 @@ describe("MatrixScheduler", function() {
             return buckets[event.getId()];
         };
 
-        let expectOrder = [
+        const expectOrder = [
             eventA.getId(), eventB.getId(), eventD.getId(),
         ];
-        let deferA = q.defer();
+        const deferA = q.defer();
         scheduler.setProcessFunction(function(event) {
-            let id = expectOrder.shift();
+            const id = expectOrder.shift();
             expect(id).toEqual(event.getId());
             if (expectOrder.length === 0) {
                 done();
@@ -201,7 +201,7 @@ describe("MatrixScheduler", function() {
             queueFn = function() {
                 return "yep";
             };
-            let prom = scheduler.queueEvent(eventA);
+            const prom = scheduler.queueEvent(eventA);
             expect(prom).toBeDefined();
             expect(prom.then).toBeDefined();
         });
@@ -229,15 +229,15 @@ describe("MatrixScheduler", function() {
             };
             scheduler.queueEvent(eventA);
             scheduler.queueEvent(eventB);
-            let queue = scheduler.getQueueForEvent(eventA);
+            const queue = scheduler.getQueueForEvent(eventA);
             expect(queue.length).toEqual(2);
             expect(queue).toEqual([eventA, eventB]);
             // modify the queue
-            let eventC = utils.mkMessage(
+            const eventC = utils.mkMessage(
                 {user: "@a:bar", room: roomId, event: true}
             );
             queue.push(eventC);
-            let queueAgain = scheduler.getQueueForEvent(eventA);
+            const queueAgain = scheduler.getQueueForEvent(eventA);
             expect(queueAgain.length).toEqual(2);
         });
 
@@ -248,9 +248,9 @@ describe("MatrixScheduler", function() {
             };
             scheduler.queueEvent(eventA);
             scheduler.queueEvent(eventB);
-            let queue = scheduler.getQueueForEvent(eventA);
+            const queue = scheduler.getQueueForEvent(eventA);
             queue[1].event.content.body = "foo";
-            let queueAgain = scheduler.getQueueForEvent(eventA);
+            const queueAgain = scheduler.getQueueForEvent(eventA);
             expect(queueAgain[1].event.content.body).toEqual("foo");
         });
     });
@@ -320,7 +320,7 @@ describe("MatrixScheduler", function() {
 
     describe("RETRY_BACKOFF_RATELIMIT", function() {
         it("should wait at least the time given on M_LIMIT_EXCEEDED", function() {
-            let res = MatrixScheduler.RETRY_BACKOFF_RATELIMIT(
+            const res = MatrixScheduler.RETRY_BACKOFF_RATELIMIT(
                 eventA, 1, new MatrixError({
                     errcode: "M_LIMIT_EXCEEDED", retry_after_ms: 5000,
                 })
@@ -329,7 +329,7 @@ describe("MatrixScheduler", function() {
         });
 
         it("should give up after 5 attempts", function() {
-            let res = MatrixScheduler.RETRY_BACKOFF_RATELIMIT(
+            const res = MatrixScheduler.RETRY_BACKOFF_RATELIMIT(
                 eventA, 5, {}
             );
             expect(res).toBe(-1, "Didn't give up.");
diff --git a/spec/unit/timeline-window.spec.js b/spec/unit/timeline-window.spec.js
index 4a0833da5..23a04bfdf 100644
--- a/spec/unit/timeline-window.spec.js
+++ b/spec/unit/timeline-window.spec.js
@@ -1,14 +1,14 @@
 "use strict";
-let q = require("q");
-let sdk = require("../..");
-let EventTimeline = sdk.EventTimeline;
-let TimelineWindow = sdk.TimelineWindow;
-let TimelineIndex = require("../../lib/timeline-window").TimelineIndex;
+const q = require("q");
+const sdk = require("../..");
+const EventTimeline = sdk.EventTimeline;
+const TimelineWindow = sdk.TimelineWindow;
+const TimelineIndex = require("../../lib/timeline-window").TimelineIndex;
 
-let utils = require("../test-utils");
+const utils = require("../test-utils");
 
-let ROOM_ID = "roomId";
-let USER_ID = "userId";
+const ROOM_ID = "roomId";
+const USER_ID = "userId";
 
 /*
  * create a timeline with a bunch (default 3) events.
@@ -23,12 +23,12 @@ function createTimeline(numEvents, baseIndex) {
     }
 
     // XXX: this is a horrid hack
-    let timelineSet = { room: { roomId: ROOM_ID }};
+    const timelineSet = { room: { roomId: ROOM_ID }};
     timelineSet.room.getUnfilteredTimelineSet = function() {
         return timelineSet;
     };
 
-    let timeline = new EventTimeline(timelineSet);
+    const timeline = new EventTimeline(timelineSet);
 
     // add the events after the baseIndex first
     addEventsToTimeline(timeline, numEvents - baseIndex, false);
@@ -56,8 +56,8 @@ function addEventsToTimeline(timeline, numEvents, atStart) {
  * create a pair of linked timelines
  */
 function createLinkedTimelines() {
-    let tl1 = createTimeline();
-    let tl2 = createTimeline();
+    const tl1 = createTimeline();
+    const tl2 = createTimeline();
     tl1.setNeighbouringTimeline(tl2, EventTimeline.FORWARDS);
     tl2.setNeighbouringTimeline(tl1, EventTimeline.BACKWARDS);
     return [tl1, tl2];
@@ -71,42 +71,42 @@ describe("TimelineIndex", function() {
 
     describe("minIndex", function() {
         it("should return the min index relative to BaseIndex", function() {
-            let timelineIndex = new TimelineIndex(createTimeline(), 0);
+            const timelineIndex = new TimelineIndex(createTimeline(), 0);
             expect(timelineIndex.minIndex()).toEqual(-1);
         });
     });
 
     describe("maxIndex", function() {
         it("should return the max index relative to BaseIndex", function() {
-            let timelineIndex = new TimelineIndex(createTimeline(), 0);
+            const timelineIndex = new TimelineIndex(createTimeline(), 0);
             expect(timelineIndex.maxIndex()).toEqual(2);
         });
     });
 
     describe("advance", function() {
         it("should advance up to the end of the timeline", function() {
-            let timelineIndex = new TimelineIndex(createTimeline(), 0);
-            let result = timelineIndex.advance(3);
+            const timelineIndex = new TimelineIndex(createTimeline(), 0);
+            const result = timelineIndex.advance(3);
             expect(result).toEqual(2);
             expect(timelineIndex.index).toEqual(2);
         });
 
         it("should retreat back to the start of the timeline", function() {
-            let timelineIndex = new TimelineIndex(createTimeline(), 0);
-            let result = timelineIndex.advance(-2);
+            const timelineIndex = new TimelineIndex(createTimeline(), 0);
+            const result = timelineIndex.advance(-2);
             expect(result).toEqual(-1);
             expect(timelineIndex.index).toEqual(-1);
         });
 
         it("should advance into the next timeline", function() {
-            let timelines = createLinkedTimelines();
-            let tl1 = timelines[0];
-            let tl2 = timelines[1];
+            const timelines = createLinkedTimelines();
+            const tl1 = timelines[0];
+            const tl2 = timelines[1];
 
             // initialise the index pointing at the end of the first timeline
-            let timelineIndex = new TimelineIndex(tl1, 2);
+            const timelineIndex = new TimelineIndex(tl1, 2);
 
-            let result = timelineIndex.advance(1);
+            const result = timelineIndex.advance(1);
             expect(result).toEqual(1);
             expect(timelineIndex.timeline).toBe(tl2);
 
@@ -117,15 +117,15 @@ describe("TimelineIndex", function() {
         });
 
         it("should retreat into the previous timeline", function() {
-            let timelines = createLinkedTimelines();
-            let tl1 = timelines[0];
-            let tl2 = timelines[1];
+            const timelines = createLinkedTimelines();
+            const tl1 = timelines[0];
+            const tl2 = timelines[1];
 
             // initialise the index pointing at the start of the second
             // timeline
-            let timelineIndex = new TimelineIndex(tl2, -1);
+            const timelineIndex = new TimelineIndex(tl2, -1);
 
-            let result = timelineIndex.advance(-1);
+            const result = timelineIndex.advance(-1);
             expect(result).toEqual(-1);
             expect(timelineIndex.timeline).toBe(tl1);
             expect(timelineIndex.index).toEqual(1);
@@ -134,8 +134,8 @@ describe("TimelineIndex", function() {
 
     describe("retreat", function() {
         it("should retreat up to the start of the timeline", function() {
-            let timelineIndex = new TimelineIndex(createTimeline(), 0);
-            let result = timelineIndex.retreat(2);
+            const timelineIndex = new TimelineIndex(createTimeline(), 0);
+            const result = timelineIndex.retreat(2);
             expect(result).toEqual(1);
             expect(timelineIndex.index).toEqual(-1);
         });
@@ -167,50 +167,50 @@ describe("TimelineWindow", function() {
 
     describe("load", function() {
         it("should initialise from the live timeline", function(done) {
-            let liveTimeline = createTimeline();
-            let room = {};
+            const liveTimeline = createTimeline();
+            const room = {};
             room.getLiveTimeline = function() {
                 return liveTimeline;
             };
 
-            let timelineWindow = new TimelineWindow(undefined, room);
+            const timelineWindow = new TimelineWindow(undefined, room);
             timelineWindow.load(undefined, 2).then(function() {
-                let expectedEvents = liveTimeline.getEvents().slice(1);
+                const expectedEvents = liveTimeline.getEvents().slice(1);
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
             }).catch(utils.failTest).done(done);
         });
 
         it("should initialise from a specific event", function(done) {
-            let timeline = createTimeline();
-            let eventId = timeline.getEvents()[1].getId();
+            const timeline = createTimeline();
+            const eventId = timeline.getEvents()[1].getId();
 
-            let timelineSet = {};
-            let client = {};
+            const timelineSet = {};
+            const client = {};
             client.getEventTimeline = function(timelineSet0, eventId0) {
                 expect(timelineSet0).toBe(timelineSet);
                 expect(eventId0).toEqual(eventId);
                 return q(timeline);
             };
 
-            let timelineWindow = new TimelineWindow(client, timelineSet);
+            const timelineWindow = new TimelineWindow(client, timelineSet);
             timelineWindow.load(eventId, 3).then(function() {
-                let expectedEvents = timeline.getEvents();
+                const expectedEvents = timeline.getEvents();
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
             }).catch(utils.failTest).done(done);
         });
 
         it("canPaginate should return false until load has returned",
            function(done) {
-            let timeline = createTimeline();
+            const timeline = createTimeline();
             timeline.setPaginationToken("toktok1", EventTimeline.BACKWARDS);
             timeline.setPaginationToken("toktok2", EventTimeline.FORWARDS);
 
-            let eventId = timeline.getEvents()[1].getId();
+            const eventId = timeline.getEvents()[1].getId();
 
-            let timelineSet = {};
-            let client = {};
+            const timelineSet = {};
+            const client = {};
 
-            let timelineWindow = new TimelineWindow(client, timelineSet);
+            const timelineWindow = new TimelineWindow(client, timelineSet);
 
             client.getEventTimeline = function(timelineSet0, eventId0) {
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -221,7 +221,7 @@ describe("TimelineWindow", function() {
             };
 
             timelineWindow.load(eventId, 3).then(function() {
-                let expectedEvents = timeline.getEvents();
+                const expectedEvents = timeline.getEvents();
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
                     .toBe(true);
@@ -234,12 +234,12 @@ describe("TimelineWindow", function() {
     describe("pagination", function() {
         it("should be able to advance across the initial timeline",
            function(done) {
-            let timeline = createTimeline();
-            let eventId = timeline.getEvents()[1].getId();
-            let timelineWindow = createWindow(timeline);
+            const timeline = createTimeline();
+            const eventId = timeline.getEvents()[1].getId();
+            const timelineWindow = createWindow(timeline);
 
             timelineWindow.load(eventId, 1).then(function() {
-                let expectedEvents = [timeline.getEvents()[1]];
+                const expectedEvents = [timeline.getEvents()[1]];
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -250,7 +250,7 @@ describe("TimelineWindow", function() {
                 return timelineWindow.paginate(EventTimeline.FORWARDS, 2);
             }).then(function(success) {
                 expect(success).toBe(true);
-                let expectedEvents = timeline.getEvents().slice(1);
+                const expectedEvents = timeline.getEvents().slice(1);
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -265,7 +265,7 @@ describe("TimelineWindow", function() {
                 return timelineWindow.paginate(EventTimeline.BACKWARDS, 2);
             }).then(function(success) {
                 expect(success).toBe(true);
-                let expectedEvents = timeline.getEvents();
+                const expectedEvents = timeline.getEvents();
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -279,12 +279,12 @@ describe("TimelineWindow", function() {
         });
 
         it("should advance into next timeline", function(done) {
-            let tls = createLinkedTimelines();
-            let eventId = tls[0].getEvents()[1].getId();
-            let timelineWindow = createWindow(tls[0], {windowLimit: 5});
+            const tls = createLinkedTimelines();
+            const eventId = tls[0].getEvents()[1].getId();
+            const timelineWindow = createWindow(tls[0], {windowLimit: 5});
 
             timelineWindow.load(eventId, 3).then(function() {
-                let expectedEvents = tls[0].getEvents();
+                const expectedEvents = tls[0].getEvents();
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -295,7 +295,7 @@ describe("TimelineWindow", function() {
                 return timelineWindow.paginate(EventTimeline.FORWARDS, 2);
             }).then(function(success) {
                 expect(success).toBe(true);
-                let expectedEvents = tls[0].getEvents()
+                const expectedEvents = tls[0].getEvents()
                     .concat(tls[1].getEvents().slice(0, 2));
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
@@ -309,7 +309,7 @@ describe("TimelineWindow", function() {
                 expect(success).toBe(true);
                 // the windowLimit should have made us drop an event from
                 // tls[0]
-                let expectedEvents = tls[0].getEvents().slice(1)
+                const expectedEvents = tls[0].getEvents().slice(1)
                     .concat(tls[1].getEvents());
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
@@ -324,12 +324,12 @@ describe("TimelineWindow", function() {
         });
 
         it("should retreat into previous timeline", function(done) {
-            let tls = createLinkedTimelines();
-            let eventId = tls[1].getEvents()[1].getId();
-            let timelineWindow = createWindow(tls[1], {windowLimit: 5});
+            const tls = createLinkedTimelines();
+            const eventId = tls[1].getEvents()[1].getId();
+            const timelineWindow = createWindow(tls[1], {windowLimit: 5});
 
             timelineWindow.load(eventId, 3).then(function() {
-                let expectedEvents = tls[1].getEvents();
+                const expectedEvents = tls[1].getEvents();
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -340,7 +340,7 @@ describe("TimelineWindow", function() {
                 return timelineWindow.paginate(EventTimeline.BACKWARDS, 2);
             }).then(function(success) {
                 expect(success).toBe(true);
-                let expectedEvents = tls[0].getEvents().slice(1, 3)
+                const expectedEvents = tls[0].getEvents().slice(1, 3)
                     .concat(tls[1].getEvents());
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
@@ -354,7 +354,7 @@ describe("TimelineWindow", function() {
                 expect(success).toBe(true);
                 // the windowLimit should have made us drop an event from
                 // tls[1]
-                let expectedEvents = tls[0].getEvents()
+                const expectedEvents = tls[0].getEvents()
                     .concat(tls[1].getEvents().slice(0, 2));
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
@@ -369,11 +369,11 @@ describe("TimelineWindow", function() {
         });
 
         it("should make forward pagination requests", function(done) {
-            let timeline = createTimeline();
+            const timeline = createTimeline();
             timeline.setPaginationToken("toktok", EventTimeline.FORWARDS);
 
-            let timelineWindow = createWindow(timeline, {windowLimit: 5});
-            let eventId = timeline.getEvents()[1].getId();
+            const timelineWindow = createWindow(timeline, {windowLimit: 5});
+            const eventId = timeline.getEvents()[1].getId();
 
             client.paginateEventTimeline = function(timeline0, opts) {
                 expect(timeline0).toBe(timeline);
@@ -385,7 +385,7 @@ describe("TimelineWindow", function() {
             };
 
             timelineWindow.load(eventId, 3).then(function() {
-                let expectedEvents = timeline.getEvents();
+                const expectedEvents = timeline.getEvents();
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -395,18 +395,18 @@ describe("TimelineWindow", function() {
                 return timelineWindow.paginate(EventTimeline.FORWARDS, 2);
             }).then(function(success) {
                 expect(success).toBe(true);
-                let expectedEvents = timeline.getEvents().slice(0, 5);
+                const expectedEvents = timeline.getEvents().slice(0, 5);
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
             }).catch(utils.failTest).done(done);
         });
 
 
         it("should make backward pagination requests", function(done) {
-            let timeline = createTimeline();
+            const timeline = createTimeline();
             timeline.setPaginationToken("toktok", EventTimeline.BACKWARDS);
 
-            let timelineWindow = createWindow(timeline, {windowLimit: 5});
-            let eventId = timeline.getEvents()[1].getId();
+            const timelineWindow = createWindow(timeline, {windowLimit: 5});
+            const eventId = timeline.getEvents()[1].getId();
 
             client.paginateEventTimeline = function(timeline0, opts) {
                 expect(timeline0).toBe(timeline);
@@ -418,7 +418,7 @@ describe("TimelineWindow", function() {
             };
 
             timelineWindow.load(eventId, 3).then(function() {
-                let expectedEvents = timeline.getEvents();
+                const expectedEvents = timeline.getEvents();
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -428,18 +428,18 @@ describe("TimelineWindow", function() {
                 return timelineWindow.paginate(EventTimeline.BACKWARDS, 2);
             }).then(function(success) {
                 expect(success).toBe(true);
-                let expectedEvents = timeline.getEvents().slice(1, 6);
+                const expectedEvents = timeline.getEvents().slice(1, 6);
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
             }).catch(utils.failTest).done(done);
         });
 
         it("should limit the number of unsuccessful pagination requests",
         function(done) {
-            let timeline = createTimeline();
+            const timeline = createTimeline();
             timeline.setPaginationToken("toktok", EventTimeline.FORWARDS);
 
-            let timelineWindow = createWindow(timeline, {windowLimit: 5});
-            let eventId = timeline.getEvents()[1].getId();
+            const timelineWindow = createWindow(timeline, {windowLimit: 5});
+            const eventId = timeline.getEvents()[1].getId();
 
             let paginateCount = 0;
             client.paginateEventTimeline = function(timeline0, opts) {
@@ -451,7 +451,7 @@ describe("TimelineWindow", function() {
             };
 
             timelineWindow.load(eventId, 3).then(function() {
-                let expectedEvents = timeline.getEvents();
+                const expectedEvents = timeline.getEvents();
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
@@ -462,7 +462,7 @@ describe("TimelineWindow", function() {
             }).then(function(success) {
                 expect(success).toBe(false);
                 expect(paginateCount).toEqual(3);
-                let expectedEvents = timeline.getEvents().slice(0, 3);
+                const expectedEvents = timeline.getEvents().slice(0, 3);
                 expect(timelineWindow.getEvents()).toEqual(expectedEvents);
 
                 expect(timelineWindow.canPaginate(EventTimeline.BACKWARDS))
diff --git a/spec/unit/user.spec.js b/spec/unit/user.spec.js
index 1ed0a0206..51a8f68d1 100644
--- a/spec/unit/user.spec.js
+++ b/spec/unit/user.spec.js
@@ -1,10 +1,10 @@
 "use strict";
-let sdk = require("../..");
-let User = sdk.User;
-let utils = require("../test-utils");
+const sdk = require("../..");
+const User = sdk.User;
+const utils = require("../test-utils");
 
 describe("User", function() {
-    let userId = "@alice:bar";
+    const userId = "@alice:bar";
     let user;
 
     beforeEach(function() {
@@ -13,7 +13,7 @@ describe("User", function() {
     });
 
     describe("setPresenceEvent", function() {
-        let event = utils.mkEvent({
+        const event = utils.mkEvent({
             type: "m.presence", content: {
                 presence: "online",
                 user_id: userId,
diff --git a/spec/unit/utils.spec.js b/spec/unit/utils.spec.js
index 0d7e31188..560c262de 100644
--- a/spec/unit/utils.spec.js
+++ b/spec/unit/utils.spec.js
@@ -1,6 +1,6 @@
 "use strict";
-let utils = require("../../lib/utils");
-let testUtils = require("../test-utils");
+const utils = require("../../lib/utils");
+const testUtils = require("../test-utils");
 
 describe("utils", function() {
     beforeEach(function() {
@@ -9,7 +9,7 @@ describe("utils", function() {
 
     describe("encodeParams", function() {
         it("should url encode and concat with &s", function() {
-            let params = {
+            const params = {
                 foo: "bar",
                 baz: "beer@",
             };
@@ -21,8 +21,8 @@ describe("utils", function() {
 
     describe("encodeUri", function() {
         it("should replace based on object keys and url encode", function() {
-            let path = "foo/bar/%something/%here";
-            let vals = {
+            const path = "foo/bar/%something/%here";
+            const vals = {
                 "%something": "baz",
                 "%here": "beer@",
             };
@@ -34,7 +34,7 @@ describe("utils", function() {
 
     describe("forEach", function() {
         it("should be invoked for each element", function() {
-            let arr = [];
+            const arr = [];
             utils.forEach([55, 66, 77], function(element) {
                 arr.push(element);
             });
@@ -44,50 +44,50 @@ describe("utils", function() {
 
     describe("findElement", function() {
         it("should find only 1 element if there is a match", function() {
-            let matchFn = function() {
+            const matchFn = function() {
                 return true;
             };
-            let arr = [55, 66, 77];
+            const arr = [55, 66, 77];
             expect(utils.findElement(arr, matchFn)).toEqual(55);
         });
         it("should be able to find in reverse order", function() {
-            let matchFn = function() {
+            const matchFn = function() {
                 return true;
             };
-            let arr = [55, 66, 77];
+            const arr = [55, 66, 77];
             expect(utils.findElement(arr, matchFn, true)).toEqual(77);
         });
         it("should find nothing if the function never returns true", function() {
-            let matchFn = function() {
+            const matchFn = function() {
                 return false;
             };
-            let arr = [55, 66, 77];
+            const arr = [55, 66, 77];
             expect(utils.findElement(arr, matchFn)).toBeFalsy();
         });
     });
 
     describe("removeElement", function() {
         it("should remove only 1 element if there is a match", function() {
-            let matchFn = function() {
+            const matchFn = function() {
                 return true;
             };
-            let arr = [55, 66, 77];
+            const arr = [55, 66, 77];
             utils.removeElement(arr, matchFn);
             expect(arr).toEqual([66, 77]);
         });
         it("should be able to remove in reverse order", function() {
-            let matchFn = function() {
+            const matchFn = function() {
                 return true;
             };
-            let arr = [55, 66, 77];
+            const arr = [55, 66, 77];
             utils.removeElement(arr, matchFn, true);
             expect(arr).toEqual([55, 66]);
         });
         it("should remove nothing if the function never returns true", function() {
-            let matchFn = function() {
+            const matchFn = function() {
                 return false;
             };
-            let arr = [55, 66, 77];
+            const arr = [55, 66, 77];
             utils.removeElement(arr, matchFn);
             expect(arr).toEqual(arr);
         });
@@ -104,7 +104,7 @@ describe("utils", function() {
             expect(utils.isFunction(555)).toBe(false);
 
             expect(utils.isFunction(function() {})).toBe(true);
-            let s = { foo: function() {} };
+            const s = { foo: function() {} };
             expect(utils.isFunction(s.foo)).toBe(true);
         });
     });
@@ -154,7 +154,7 @@ describe("utils", function() {
     });
 
     describe("deepCompare", function() {
-        let assert = {
+        const assert = {
             isTrue: function(x) {
                 expect(x).toBe(true);
             },
@@ -174,7 +174,7 @@ describe("utils", function() {
         it("should handle regexps", function() {
             assert.isTrue(utils.deepCompare(/abc/, /abc/));
             assert.isFalse(utils.deepCompare(/abc/, /123/));
-            let r = /abc/;
+            const r = /abc/;
             assert.isTrue(utils.deepCompare(r, r));
         });
 
@@ -216,10 +216,10 @@ describe("utils", function() {
             // no two different function is equal really, they capture their
             // context variables so even if they have same toString(), they
             // won't have same functionality
-            let func = function(x) {
+            const func = function(x) {
                 return true;
             };
-            let func2 = function(x) {
+            const func2 = function(x) {
                 return true;
             };
             assert.isTrue(utils.deepCompare(func, func));
@@ -231,17 +231,17 @@ describe("utils", function() {
 
 
     describe("extend", function() {
-        let SOURCE = { "prop2": 1, "string2": "x", "newprop": "new" };
+        const SOURCE = { "prop2": 1, "string2": "x", "newprop": "new" };
 
         it("should extend", function() {
-            let target = {
+            const target = {
                 "prop1": 5, "prop2": 7, "string1": "baz", "string2": "foo",
             };
-            let merged = {
+            const merged = {
                 "prop1": 5, "prop2": 1, "string1": "baz", "string2": "x",
                 "newprop": "new",
             };
-            let sourceOrig = JSON.stringify(SOURCE);
+            const sourceOrig = JSON.stringify(SOURCE);
 
             utils.extend(target, SOURCE);
             expect(JSON.stringify(target)).toEqual(JSON.stringify(merged));
@@ -251,14 +251,14 @@ describe("utils", function() {
         });
 
         it("should ignore null", function() {
-            let target = {
+            const target = {
                 "prop1": 5, "prop2": 7, "string1": "baz", "string2": "foo",
             };
-            let merged = {
+            const merged = {
                 "prop1": 5, "prop2": 1, "string1": "baz", "string2": "x",
                 "newprop": "new",
             };
-            let sourceOrig = JSON.stringify(SOURCE);
+            const sourceOrig = JSON.stringify(SOURCE);
 
             utils.extend(target, null, SOURCE);
             expect(JSON.stringify(target)).toEqual(JSON.stringify(merged));
@@ -268,7 +268,7 @@ describe("utils", function() {
         });
 
         it("should handle properties created with defineProperties", function() {
-            let source = Object.defineProperties({}, {
+            const source = Object.defineProperties({}, {
                 "enumerableProp": {
                     get: function() {
                         return true;
@@ -282,7 +282,7 @@ describe("utils", function() {
                 },
             });
 
-            let target = {};
+            const target = {};
             utils.extend(target, source);
             expect(target.enumerableProp).toBe(true);
             expect(target.nonenumerableProp).toBe(undefined);
diff --git a/src/base-apis.js b/src/base-apis.js
index 76c64a545..54a9d67be 100644
--- a/src/base-apis.js
+++ b/src/base-apis.js
@@ -22,8 +22,8 @@ limitations under the License.
  * @module base-apis
  */
 
-let httpApi = require("./http-api");
-let utils = require("./utils");
+const httpApi = require("./http-api");
+const utils = require("./utils");
 
 /**
  * Low-level wrappers for the Matrix APIs
@@ -60,7 +60,7 @@ function MatrixBaseApis(opts) {
     this.baseUrl = opts.baseUrl;
     this.idBaseUrl = opts.idBaseUrl;
 
-    let httpOpts = {
+    const httpOpts = {
         baseUrl: opts.baseUrl,
         idBaseUrl: opts.idBaseUrl,
         accessToken: opts.accessToken,
@@ -142,7 +142,7 @@ MatrixBaseApis.prototype.register = function(
         auth.session = sessionId;
     }
 
-    let params = {
+    const params = {
         auth: auth,
     };
     if (username !== undefined && username !== null) {
@@ -183,7 +183,7 @@ MatrixBaseApis.prototype.registerGuest = function(opts, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.registerRequest = function(data, kind, callback) {
-    let params = {};
+    const params = {};
     if (kind) {
         params.kind = kind;
     }
@@ -210,7 +210,7 @@ MatrixBaseApis.prototype.loginFlows = function(callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.login = function(loginType, data, callback) {
-    let login_data = {
+    const login_data = {
         type: loginType,
     };
 
@@ -318,7 +318,7 @@ MatrixBaseApis.prototype.deactivateAccount = function(auth, callback) {
  * @return {string} HS URL to hit to for the fallback interface
  */
 MatrixBaseApis.prototype.getFallbackAuthUrl = function(loginType, authSessionId) {
-    let path = utils.encodeUri("/auth/$loginType/fallback/web", {
+    const path = utils.encodeUri("/auth/$loginType/fallback/web", {
         $loginType: loginType,
     });
 
@@ -358,7 +358,7 @@ MatrixBaseApis.prototype.createRoom = function(options, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.roomState = function(roomId, callback) {
-    let path = utils.encodeUri("/rooms/$roomId/state", {$roomId: roomId});
+    const path = utils.encodeUri("/rooms/$roomId/state", {$roomId: roomId});
     return this._http.authedRequest(callback, "GET", path);
 };
 
@@ -372,7 +372,7 @@ MatrixBaseApis.prototype.roomState = function(roomId, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.getStateEvent = function(roomId, eventType, stateKey, callback) {
-    let pathParams = {
+    const pathParams = {
         $roomId: roomId,
         $eventType: eventType,
         $stateKey: stateKey,
@@ -397,7 +397,7 @@ MatrixBaseApis.prototype.getStateEvent = function(roomId, eventType, stateKey, c
  */
 MatrixBaseApis.prototype.sendStateEvent = function(roomId, eventType, content, stateKey,
                                                  callback) {
-    let pathParams = {
+    const pathParams = {
         $roomId: roomId,
         $eventType: eventType,
         $stateKey: stateKey,
@@ -419,7 +419,7 @@ MatrixBaseApis.prototype.sendStateEvent = function(roomId, eventType, content, s
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.redactEvent = function(roomId, eventId, callback) {
-    let path = utils.encodeUri("/rooms/$roomId/redact/$eventId", {
+    const path = utils.encodeUri("/rooms/$roomId/redact/$eventId", {
         $roomId: roomId,
         $eventId: eventId,
     });
@@ -437,7 +437,7 @@ MatrixBaseApis.prototype.roomInitialSync = function(roomId, limit, callback) {
     if (utils.isFunction(limit)) {
         callback = limit; limit = undefined;
     }
-    let path = utils.encodeUri("/rooms/$roomId/initialSync",
+    const path = utils.encodeUri("/rooms/$roomId/initialSync",
         {$roomId: roomId}
     );
     if (!limit) {
@@ -474,7 +474,7 @@ MatrixBaseApis.prototype.publicRooms = function(options, callback) {
         options = {};
     }
 
-    let query_params = {};
+    const query_params = {};
     if (options.server) {
         query_params.server = options.server;
         delete options.server;
@@ -498,10 +498,10 @@ MatrixBaseApis.prototype.publicRooms = function(options, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.createAlias = function(alias, roomId, callback) {
-    let path = utils.encodeUri("/directory/room/$alias", {
+    const path = utils.encodeUri("/directory/room/$alias", {
         $alias: alias,
     });
-    let data = {
+    const data = {
         room_id: roomId,
     };
     return this._http.authedRequest(
@@ -518,7 +518,7 @@ MatrixBaseApis.prototype.createAlias = function(alias, roomId, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.deleteAlias = function(alias, callback) {
-    let path = utils.encodeUri("/directory/room/$alias", {
+    const path = utils.encodeUri("/directory/room/$alias", {
         $alias: alias,
     });
     return this._http.authedRequest(
@@ -535,7 +535,7 @@ MatrixBaseApis.prototype.deleteAlias = function(alias, callback) {
  */
 MatrixBaseApis.prototype.getRoomIdForAlias = function(alias, callback) {
     // TODO: deprecate this or resolveRoomAlias
-    let path = utils.encodeUri("/directory/room/$alias", {
+    const path = utils.encodeUri("/directory/room/$alias", {
         $alias: alias,
     });
     return this._http.authedRequest(
@@ -551,7 +551,7 @@ MatrixBaseApis.prototype.getRoomIdForAlias = function(alias, callback) {
  */
 MatrixBaseApis.prototype.resolveRoomAlias = function(roomAlias, callback) {
     // TODO: deprecate this or getRoomIdForAlias
-    let path = utils.encodeUri("/directory/room/$alias", {$alias: roomAlias});
+    const path = utils.encodeUri("/directory/room/$alias", {$alias: roomAlias});
     return this._http.request(callback, "GET", path);
 };
 
@@ -564,7 +564,7 @@ MatrixBaseApis.prototype.resolveRoomAlias = function(roomAlias, callback) {
  */
 MatrixBaseApis.prototype.getRoomDirectoryVisibility =
                                 function(roomId, callback) {
-    let path = utils.encodeUri("/directory/list/room/$roomId", {
+    const path = utils.encodeUri("/directory/list/room/$roomId", {
         $roomId: roomId,
     });
     return this._http.authedRequest(callback, "GET", path);
@@ -582,7 +582,7 @@ MatrixBaseApis.prototype.getRoomDirectoryVisibility =
  */
 MatrixBaseApis.prototype.setRoomDirectoryVisibility =
                                 function(roomId, visibility, callback) {
-    let path = utils.encodeUri("/directory/list/room/$roomId", {
+    const path = utils.encodeUri("/directory/list/room/$roomId", {
         $roomId: roomId,
     });
     return this._http.authedRequest(
@@ -605,7 +605,7 @@ MatrixBaseApis.prototype.setRoomDirectoryVisibility =
  */
 MatrixBaseApis.prototype.setRoomDirectoryVisibilityAppService =
                                 function(networkId, roomId, visibility, callback) {
-    let path = utils.encodeUri("/directory/list/appservice/$networkId/$roomId", {
+    const path = utils.encodeUri("/directory/list/appservice/$networkId/$roomId", {
         $networkId: networkId,
         $roomId: roomId,
     });
@@ -692,7 +692,7 @@ MatrixBaseApis.prototype.getProfileInfo = function(userId, info, callback) {
         callback = info; info = undefined;
     }
 
-    let path = info ?
+    const path = info ?
     utils.encodeUri("/profile/$userId/$info",
              { $userId: userId, $info: info }) :
     utils.encodeUri("/profile/$userId",
@@ -710,7 +710,7 @@ MatrixBaseApis.prototype.getProfileInfo = function(userId, info, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.getThreePids = function(callback) {
-    let path = "/account/3pid";
+    const path = "/account/3pid";
     return this._http.authedRequest(
         callback, "GET", path, undefined, undefined
     );
@@ -724,8 +724,8 @@ MatrixBaseApis.prototype.getThreePids = function(callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.addThreePid = function(creds, bind, callback) {
-    let path = "/account/3pid";
-    let data = {
+    const path = "/account/3pid";
+    const data = {
         'threePidCreds': creds,
         'bind': bind,
     };
@@ -743,8 +743,8 @@ MatrixBaseApis.prototype.addThreePid = function(creds, bind, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.deleteThreePid = function(medium, address) {
-    let path = "/account/3pid/delete";
-    let data = {
+    const path = "/account/3pid/delete";
+    const data = {
         'medium': medium,
         'address': address,
     };
@@ -762,8 +762,8 @@ MatrixBaseApis.prototype.deleteThreePid = function(medium, address) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.setPassword = function(authDict, newPassword, callback) {
-    let path = "/account/password";
-    let data = {
+    const path = "/account/password";
+    const data = {
         'auth': authDict,
         'new_password': newPassword,
     };
@@ -783,7 +783,7 @@ MatrixBaseApis.prototype.setPassword = function(authDict, newPassword, callback)
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.getDevices = function() {
-    let path = "/devices";
+    const path = "/devices";
     return this._http.authedRequestWithPrefix(
         undefined, "GET", path, undefined, undefined,
         httpApi.PREFIX_UNSTABLE
@@ -799,7 +799,7 @@ MatrixBaseApis.prototype.getDevices = function() {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.setDeviceDetails = function(device_id, body) {
-    let path = utils.encodeUri("/devices/$device_id", {
+    const path = utils.encodeUri("/devices/$device_id", {
         $device_id: device_id,
     });
 
@@ -819,11 +819,11 @@ MatrixBaseApis.prototype.setDeviceDetails = function(device_id, body) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.deleteDevice = function(device_id, auth) {
-    let path = utils.encodeUri("/devices/$device_id", {
+    const path = utils.encodeUri("/devices/$device_id", {
         $device_id: device_id,
     });
 
-    let body = {};
+    const body = {};
 
     if (auth) {
         body.auth = auth;
@@ -847,7 +847,7 @@ MatrixBaseApis.prototype.deleteDevice = function(device_id, auth) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.getPushers = function(callback) {
-    let path = "/pushers";
+    const path = "/pushers";
     return this._http.authedRequest(
         callback, "GET", path, undefined, undefined
     );
@@ -862,7 +862,7 @@ MatrixBaseApis.prototype.getPushers = function(callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.setPusher = function(pusher, callback) {
-    let path = "/pushers/set";
+    const path = "/pushers/set";
     return this._http.authedRequest(
         callback, "POST", path, null, pusher
     );
@@ -888,7 +888,7 @@ MatrixBaseApis.prototype.getPushRules = function(callback) {
  */
 MatrixBaseApis.prototype.addPushRule = function(scope, kind, ruleId, body, callback) {
     // NB. Scope not uri encoded because devices need the '/'
-    let path = utils.encodeUri("/pushrules/" + scope + "/$kind/$ruleId", {
+    const path = utils.encodeUri("/pushrules/" + scope + "/$kind/$ruleId", {
         $kind: kind,
         $ruleId: ruleId,
     });
@@ -907,7 +907,7 @@ MatrixBaseApis.prototype.addPushRule = function(scope, kind, ruleId, body, callb
  */
 MatrixBaseApis.prototype.deletePushRule = function(scope, kind, ruleId, callback) {
     // NB. Scope not uri encoded because devices need the '/'
-    let path = utils.encodeUri("/pushrules/" + scope + "/$kind/$ruleId", {
+    const path = utils.encodeUri("/pushrules/" + scope + "/$kind/$ruleId", {
         $kind: kind,
         $ruleId: ruleId,
     });
@@ -926,7 +926,7 @@ MatrixBaseApis.prototype.deletePushRule = function(scope, kind, ruleId, callback
  */
 MatrixBaseApis.prototype.setPushRuleEnabled = function(scope, kind,
                                                      ruleId, enabled, callback) {
-    let path = utils.encodeUri("/pushrules/" + scope + "/$kind/$ruleId/enabled", {
+    const path = utils.encodeUri("/pushrules/" + scope + "/$kind/$ruleId/enabled", {
         $kind: kind,
         $ruleId: ruleId,
     });
@@ -947,7 +947,7 @@ MatrixBaseApis.prototype.setPushRuleEnabled = function(scope, kind,
  */
 MatrixBaseApis.prototype.setPushRuleActions = function(scope, kind,
                                                      ruleId, actions, callback) {
-    let path = utils.encodeUri("/pushrules/" + scope + "/$kind/$ruleId/actions", {
+    const path = utils.encodeUri("/pushrules/" + scope + "/$kind/$ruleId/actions", {
         $kind: kind,
         $ruleId: ruleId,
     });
@@ -970,7 +970,7 @@ MatrixBaseApis.prototype.setPushRuleActions = function(scope, kind,
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.search = function(opts, callback) {
-    let queryparams = {};
+    const queryparams = {};
     if (opts.next_batch) {
         queryparams.next_batch = opts.next_batch;
     }
@@ -999,7 +999,7 @@ MatrixBaseApis.prototype.search = function(opts, callback) {
  */
 MatrixBaseApis.prototype.uploadKeysRequest = function(content, opts, callback) {
     opts = opts || {};
-    let deviceId = opts.device_id;
+    const deviceId = opts.device_id;
     let path;
     if (deviceId) {
         path = utils.encodeUri("/keys/upload/$deviceId", {
@@ -1024,12 +1024,12 @@ MatrixBaseApis.prototype.uploadKeysRequest = function(content, opts, callback) {
  *     an error response ({@link module:http-api.MatrixError}).
  */
 MatrixBaseApis.prototype.downloadKeysForUsers = function(userIds, callback) {
-    let downloadQuery = {};
+    const downloadQuery = {};
 
     for (let i = 0; i < userIds.length; ++i) {
         downloadQuery[userIds[i]] = {};
     }
-    let content = {device_keys: downloadQuery};
+    const content = {device_keys: downloadQuery};
     return this._http.authedRequestWithPrefix(
         callback, "POST", "/keys/query", undefined, content,
         httpApi.PREFIX_UNSTABLE
@@ -1047,20 +1047,20 @@ MatrixBaseApis.prototype.downloadKeysForUsers = function(userIds, callback) {
  *     an error response ({@link module:http-api.MatrixError}).
  */
 MatrixBaseApis.prototype.claimOneTimeKeys = function(devices, key_algorithm) {
-    let queries = {};
+    const queries = {};
 
     if (key_algorithm === undefined) {
         key_algorithm = "signed_curve25519";
     }
 
     for (let i = 0; i < devices.length; ++i) {
-        let userId = devices[i][0];
-        let deviceId = devices[i][1];
-        let query = queries[userId] || {};
+        const userId = devices[i][0];
+        const deviceId = devices[i][1];
+        const query = queries[userId] || {};
         queries[userId] = query;
         query[deviceId] = key_algorithm;
     }
-    let content = {one_time_keys: queries};
+    const content = {one_time_keys: queries};
     return this._http.authedRequestWithPrefix(
         undefined, "POST", "/keys/claim", undefined, content,
         httpApi.PREFIX_UNSTABLE
@@ -1093,7 +1093,7 @@ MatrixBaseApis.prototype.claimOneTimeKeys = function(devices, key_algorithm) {
  */
 MatrixBaseApis.prototype.requestEmailToken = function(email, clientSecret,
                                                     sendAttempt, nextLink, callback) {
-    let params = {
+    const params = {
         client_secret: clientSecret,
         email: email,
         send_attempt: sendAttempt,
@@ -1117,7 +1117,7 @@ MatrixBaseApis.prototype.requestEmailToken = function(email, clientSecret,
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixBaseApis.prototype.lookupThreePid = function(medium, address, callback) {
-    let params = {
+    const params = {
         medium: medium,
         address: address,
     };
@@ -1144,12 +1144,12 @@ MatrixBaseApis.prototype.lookupThreePid = function(medium, address, callback) {
 MatrixBaseApis.prototype.sendToDevice = function(
     eventType, contentMap, txnId
 ) {
-    let path = utils.encodeUri("/sendToDevice/$eventType/$txnId", {
+    const path = utils.encodeUri("/sendToDevice/$eventType/$txnId", {
         $eventType: eventType,
         $txnId: txnId ? txnId : this.makeTxnId(),
     });
 
-    let body = {
+    const body = {
         messages: contentMap,
     };
 
@@ -1183,7 +1183,7 @@ MatrixBaseApis.prototype.getThirdpartyProtocols = function() {
  * @return {module:client.Promise} Resolves to the result object
  */
 MatrixBaseApis.prototype.getThirdpartyLocation = function(protocol, params) {
-    let path = utils.encodeUri("/thirdparty/location/$protocol", {
+    const path = utils.encodeUri("/thirdparty/location/$protocol", {
         $protocol: protocol,
     });
 
diff --git a/src/client.js b/src/client.js
index 13a1e1cc7..4e78c01c1 100644
--- a/src/client.js
+++ b/src/client.js
@@ -15,31 +15,31 @@ limitations under the License.
 */
 "use strict";
 
-let PushProcessor = require('./pushprocessor');
+const PushProcessor = require('./pushprocessor');
 
 /**
  * This is an internal module. See {@link MatrixClient} for the public class.
  * @module client
  */
-let EventEmitter = require("events").EventEmitter;
-let q = require("q");
-let url = require('url');
+const EventEmitter = require("events").EventEmitter;
+const q = require("q");
+const url = require('url');
 
-let httpApi = require("./http-api");
-let MatrixEvent = require("./models/event").MatrixEvent;
-let EventStatus = require("./models/event").EventStatus;
-let EventTimeline = require("./models/event-timeline");
-let SearchResult = require("./models/search-result");
-let StubStore = require("./store/stub");
-let webRtcCall = require("./webrtc/call");
-let utils = require("./utils");
-let contentRepo = require("./content-repo");
-let Filter = require("./filter");
-let SyncApi = require("./sync");
-let MatrixBaseApis = require("./base-apis");
-let MatrixError = httpApi.MatrixError;
+const httpApi = require("./http-api");
+const MatrixEvent = require("./models/event").MatrixEvent;
+const EventStatus = require("./models/event").EventStatus;
+const EventTimeline = require("./models/event-timeline");
+const SearchResult = require("./models/search-result");
+const StubStore = require("./store/stub");
+const webRtcCall = require("./webrtc/call");
+const utils = require("./utils");
+const contentRepo = require("./content-repo");
+const Filter = require("./filter");
+const SyncApi = require("./sync");
+const MatrixBaseApis = require("./base-apis");
+const MatrixError = httpApi.MatrixError;
 
-let SCROLLBACK_DELAY_MS = 3000;
+const SCROLLBACK_DELAY_MS = 3000;
 let CRYPTO_ENABLED = false;
 
 try {
@@ -111,16 +111,16 @@ function MatrixClient(opts) {
 
     this.deviceId = opts.deviceId || null;
 
-    let userId = (opts.userId || null);
+    const userId = (opts.userId || null);
     this.credentials = {
         userId: userId,
     };
 
     this.scheduler = opts.scheduler;
     if (this.scheduler) {
-        let self = this;
+        const self = this;
         this.scheduler.setProcessFunction(function(eventToSend) {
-            let room = self.getRoom(eventToSend.getRoomId());
+            const room = self.getRoom(eventToSend.getRoomId());
             if (eventToSend.status !== EventStatus.SENDING) {
                 _updatePendingEventStatus(room, eventToSend,
                                           EventStatus.SENDING);
@@ -136,7 +136,7 @@ function MatrixClient(opts) {
 
     // try constructing a MatrixCall to see if we are running in an environment
     // which has WebRTC. If we are, listen for and handle m.call.* events.
-    let call = webRtcCall.createNewMatrixCall(this);
+    const call = webRtcCall.createNewMatrixCall(this);
     this._supportsVoip = false;
     if (call) {
         setupCallEventHandler(this);
@@ -427,7 +427,7 @@ MatrixClient.prototype.getEventSenderDeviceInfo = function(event) {
  * {@link module:client~MatrixClient#setDeviceVerified|setDeviceVerified}.
  */
 MatrixClient.prototype.isEventSenderVerified = function(event) {
-    let device = this.getEventSenderDeviceInfo(event);
+    const device = this.getEventSenderDeviceInfo(event);
     if (!device) {
         return false;
     }
@@ -574,7 +574,7 @@ MatrixClient.prototype.getUsers = function() {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.setAccountData = function(eventType, contents, callback) {
-    let path = utils.encodeUri("/user/$userId/account_data/$type", {
+    const path = utils.encodeUri("/user/$userId/account_data/$type", {
         $userId: this.credentials.userId,
         $type: eventType,
     });
@@ -619,7 +619,7 @@ MatrixClient.prototype.joinRoom = function(roomIdOrAlias, opts, callback) {
         opts.syncRoom = true;
     }
 
-    let room = this.getRoom(roomIdOrAlias);
+    const room = this.getRoom(roomIdOrAlias);
     if (room && room.hasMembershipState(this.credentials.userId, "join")) {
         return q(room);
     }
@@ -633,21 +633,21 @@ MatrixClient.prototype.joinRoom = function(roomIdOrAlias, opts, callback) {
         );
     }
 
-    let defer = q.defer();
+    const defer = q.defer();
 
-    let self = this;
+    const self = this;
     sign_promise.then(function(signed_invite_object) {
-        let data = {};
+        const data = {};
         if (signed_invite_object) {
             data.third_party_signed = signed_invite_object;
         }
 
-        let path = utils.encodeUri("/join/$roomid", { $roomid: roomIdOrAlias});
+        const path = utils.encodeUri("/join/$roomid", { $roomid: roomIdOrAlias});
         return self._http.authedRequest(undefined, "POST", path, undefined, data);
     }).then(function(res) {
-        let roomId = res.room_id;
-        let syncApi = new SyncApi(self, self._clientOpts);
-        let room = syncApi.createRoom(roomId);
+        const roomId = res.room_id;
+        const syncApi = new SyncApi(self, self._clientOpts);
+        const room = syncApi.createRoom(roomId);
         if (opts.syncRoom) {
             // v2 will do this for us
             // return syncApi.syncRoom(room);
@@ -692,7 +692,7 @@ MatrixClient.prototype.cancelPendingEvent = function(event) {
 
     // then tell the room about the change of state, which will remove it
     // from the room's list of pending events.
-    let room = this.getRoom(event.getRoomId());
+    const room = this.getRoom(event.getRoomId());
     _updatePendingEventStatus(room, event, EventStatus.CANCELLED);
 };
 
@@ -727,7 +727,7 @@ MatrixClient.prototype.setRoomTopic = function(roomId, topic, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.getRoomTags = function(roomId, callback) {
-    let path = utils.encodeUri("/user/$userId/rooms/$roomId/tags/", {
+    const path = utils.encodeUri("/user/$userId/rooms/$roomId/tags/", {
         $userId: this.credentials.userId,
         $roomId: roomId,
     });
@@ -745,7 +745,7 @@ MatrixClient.prototype.getRoomTags = function(roomId, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.setRoomTag = function(roomId, tagName, metadata, callback) {
-    let path = utils.encodeUri("/user/$userId/rooms/$roomId/tags/$tag", {
+    const path = utils.encodeUri("/user/$userId/rooms/$roomId/tags/$tag", {
         $userId: this.credentials.userId,
         $roomId: roomId,
         $tag: tagName,
@@ -763,7 +763,7 @@ MatrixClient.prototype.setRoomTag = function(roomId, tagName, metadata, callback
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.deleteRoomTag = function(roomId, tagName, callback) {
-    let path = utils.encodeUri("/user/$userId/rooms/$roomId/tags/$tag", {
+    const path = utils.encodeUri("/user/$userId/rooms/$roomId/tags/$tag", {
         $userId: this.credentials.userId,
         $roomId: roomId,
         $tag: tagName,
@@ -783,7 +783,7 @@ MatrixClient.prototype.deleteRoomTag = function(roomId, tagName, callback) {
  */
 MatrixClient.prototype.setRoomAccountData = function(roomId, eventType,
                                                      content, callback) {
-    let path = utils.encodeUri("/user/$userId/rooms/$roomId/account_data/$type", {
+    const path = utils.encodeUri("/user/$userId/rooms/$roomId/account_data/$type", {
         $userId: this.credentials.userId,
         $roomId: roomId,
         $type: eventType,
@@ -814,7 +814,7 @@ MatrixClient.prototype.setPowerLevel = function(roomId, userId, powerLevel,
         content = utils.deepCopy(event.getContent());
     }
     content.users[userId] = powerLevel;
-    let path = utils.encodeUri("/rooms/$roomId/state/m.room.power_levels", {
+    const path = utils.encodeUri("/rooms/$roomId/state/m.room.power_levels", {
         $roomId: roomId,
     });
     return this._http.authedRequest(
@@ -844,8 +844,8 @@ MatrixClient.prototype.sendEvent = function(roomId, eventType, content, txnId,
     // we always construct a MatrixEvent when sending because the store and
     // scheduler use them. We'll extract the params back out if it turns out
     // the client has no scheduler or store.
-    let room = this.getRoom(roomId);
-    let localEvent = new MatrixEvent({
+    const room = this.getRoom(roomId);
+    const localEvent = new MatrixEvent({
         event_id: "~" + roomId + ":" + txnId,
         user_id: this.credentials.userId,
         room_id: roomId,
@@ -939,9 +939,9 @@ function _updatePendingEventStatus(room, event, newStatus) {
 }
 
 function _sendEventHttpRequest(client, event) {
-    let txnId = event._txnId ? event._txnId : client.makeTxnId();
+    const txnId = event._txnId ? event._txnId : client.makeTxnId();
 
-    let pathParams = {
+    const pathParams = {
         $roomId: event.getRoomId(),
         $eventType: event.getWireType(),
         $stateKey: event.getStateKey(),
@@ -993,7 +993,7 @@ MatrixClient.prototype.sendMessage = function(roomId, content, txnId, callback)
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.sendTextMessage = function(roomId, body, txnId, callback) {
-    let content = {
+    const content = {
          msgtype: "m.text",
          body: body,
     };
@@ -1009,7 +1009,7 @@ MatrixClient.prototype.sendTextMessage = function(roomId, body, txnId, callback)
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.sendNotice = function(roomId, body, txnId, callback) {
-    let content = {
+    const content = {
          msgtype: "m.notice",
          body: body,
     };
@@ -1025,7 +1025,7 @@ MatrixClient.prototype.sendNotice = function(roomId, body, txnId, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.sendEmoteMessage = function(roomId, body, txnId, callback) {
-    let content = {
+    const content = {
          msgtype: "m.emote",
          body: body,
     };
@@ -1048,7 +1048,7 @@ MatrixClient.prototype.sendImageMessage = function(roomId, url, info, text, call
     if (!text) {
         text = "Image";
     }
-    let content = {
+    const content = {
          msgtype: "m.image",
          url: url,
          info: info,
@@ -1066,7 +1066,7 @@ MatrixClient.prototype.sendImageMessage = function(roomId, url, info, text, call
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.sendHtmlMessage = function(roomId, body, htmlBody, callback) {
-    let content = {
+    const content = {
         msgtype: "m.text",
         format: "org.matrix.custom.html",
         body: body,
@@ -1084,7 +1084,7 @@ MatrixClient.prototype.sendHtmlMessage = function(roomId, body, htmlBody, callba
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.sendHtmlNotice = function(roomId, body, htmlBody, callback) {
-    let content = {
+    const content = {
         msgtype: "m.notice",
         format: "org.matrix.custom.html",
         body: body,
@@ -1102,7 +1102,7 @@ MatrixClient.prototype.sendHtmlNotice = function(roomId, body, htmlBody, callbac
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.sendHtmlEmote = function(roomId, body, htmlBody, callback) {
-    let content = {
+    const content = {
         msgtype: "m.emote",
         format: "org.matrix.custom.html",
         body: body,
@@ -1124,16 +1124,16 @@ MatrixClient.prototype.sendReceipt = function(event, receiptType, callback) {
         return q({}); // guests cannot send receipts so don't bother.
     }
 
-    let path = utils.encodeUri("/rooms/$roomId/receipt/$receiptType/$eventId", {
+    const path = utils.encodeUri("/rooms/$roomId/receipt/$receiptType/$eventId", {
         $roomId: event.getRoomId(),
         $receiptType: receiptType,
         $eventId: event.getId(),
     });
-    let promise = this._http.authedRequest(
+    const promise = this._http.authedRequest(
         callback, "POST", path, undefined, {}
     );
 
-    let room = this.getRoom(event.getRoomId());
+    const room = this.getRoom(event.getRoomId());
     if (room) {
         room._addLocalEchoReceipt(this.credentials.userId, event, receiptType);
     }
@@ -1168,13 +1168,13 @@ MatrixClient.prototype.sendReadReceipt = function(event, callback) {
  * May return synthesized attributes if the URL lacked OG meta.
  */
 MatrixClient.prototype.getUrlPreview = function(url, ts, callback) {
-    let key = ts + "_" + url;
-    let og = this.urlPreviewCache[key];
+    const key = ts + "_" + url;
+    const og = this.urlPreviewCache[key];
     if (og) {
         return q(og);
     }
 
-    let self = this;
+    const self = this;
     return this._http.authedRequestWithPrefix(
         callback, "GET", "/preview_url", {
             url: url,
@@ -1200,11 +1200,11 @@ MatrixClient.prototype.sendTyping = function(roomId, isTyping, timeoutMs, callba
         return q({}); // guests cannot send typing notifications so don't bother.
     }
 
-    let path = utils.encodeUri("/rooms/$roomId/typing/$userId", {
+    const path = utils.encodeUri("/rooms/$roomId/typing/$userId", {
         $roomId: roomId,
         $userId: this.credentials.userId,
     });
-    let data = {
+    const data = {
         typing: isTyping,
     };
     if (isTyping) {
@@ -1251,7 +1251,7 @@ MatrixClient.prototype.inviteByEmail = function(roomId, email, callback) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.inviteByThreePid = function(roomId, medium, address, callback) {
-    let path = utils.encodeUri(
+    const path = utils.encodeUri(
         "/rooms/$roomId/invite",
         { $roomId: roomId }
     );
@@ -1312,12 +1312,12 @@ MatrixClient.prototype.forget = function(roomId, deleteRoom, callback) {
     if (deleteRoom === undefined) {
         deleteRoom = true;
     }
-    let promise = _membershipChange(this, roomId, undefined, "forget", undefined,
+    const promise = _membershipChange(this, roomId, undefined, "forget", undefined,
         callback);
     if (!deleteRoom) {
         return promise;
     }
-    let self = this;
+    const self = this;
     return promise.then(function(response) {
         self.store.removeRoom(roomId);
         self.emit("deleteRoom", roomId);
@@ -1370,7 +1370,7 @@ function _setMembershipState(client, roomId, userId, membershipValue, reason,
         callback = reason; reason = undefined;
     }
 
-    let path = utils.encodeUri(
+    const path = utils.encodeUri(
         "/rooms/$roomId/state/m.room.member/$userId",
         { $roomId: roomId, $userId: userId}
     );
@@ -1397,7 +1397,7 @@ function _membershipChange(client, roomId, userId, membership, reason, callback)
         callback = reason; reason = undefined;
     }
 
-    let path = utils.encodeUri("/rooms/$room_id/$membership", {
+    const path = utils.encodeUri("/rooms/$room_id/$membership", {
         $room_id: roomId,
         $membership: membership,
     });
@@ -1417,7 +1417,7 @@ function _membershipChange(client, roomId, userId, membership, reason, callback)
  */
 MatrixClient.prototype.getPushActionsForEvent = function(event) {
     if (!event.getPushActions()) {
-        let pushProcessor = new PushProcessor(this);
+        const pushProcessor = new PushProcessor(this);
         event.setPushActions(pushProcessor.actionsForEvent(event));
     }
     return event.getPushActions();
@@ -1434,7 +1434,7 @@ MatrixClient.prototype.getPushActionsForEvent = function(event) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.setProfileInfo = function(info, data, callback) {
-    let path = utils.encodeUri("/profile/$userId/$info", {
+    const path = utils.encodeUri("/profile/$userId/$info", {
         $userId: this.credentials.userId,
         $info: info,
     });
@@ -1497,7 +1497,7 @@ MatrixClient.prototype.mxcUrlToHttp =
  * @throws If 'presence' isn't a valid presence enum value.
  */
 MatrixClient.prototype.setPresence = function(opts, callback) {
-    let path = utils.encodeUri("/presence/$userId/status", {
+    const path = utils.encodeUri("/presence/$userId/status", {
         $userId: this.credentials.userId,
     });
 
@@ -1505,7 +1505,7 @@ MatrixClient.prototype.setPresence = function(opts, callback) {
       opts = { presence: opts };
     }
 
-    let validStates = ["offline", "online", "unavailable"];
+    const validStates = ["offline", "online", "unavailable"];
     if (validStates.indexOf(opts.presence) == -1) {
         throw new Error("Bad presence value: " + opts.presence);
     }
@@ -1515,7 +1515,7 @@ MatrixClient.prototype.setPresence = function(opts, callback) {
 };
 
 function _presenceList(callback, client, opts, method) {
-  let path = utils.encodeUri("/presence/list/$userId", {
+  const path = utils.encodeUri("/presence/list/$userId", {
       $userId: client.credentials.userId,
   });
   return client._http.authedRequest(callback, method, path, undefined, opts);
@@ -1539,7 +1539,7 @@ MatrixClient.prototype.getPresenceList = function(callback) {
 * @return {module:http-api.MatrixError} Rejects: with an error response.
 */
 MatrixClient.prototype.inviteToPresenceList = function(callback, userIds) {
-  let opts = {"invite": userIds};
+  const opts = {"invite": userIds};
   return _presenceList(callback, this, opts, "POST");
 };
 
@@ -1551,7 +1551,7 @@ MatrixClient.prototype.inviteToPresenceList = function(callback, userIds) {
 * @return {module:http-api.MatrixError} Rejects: with an error response.
 **/
 MatrixClient.prototype.dropFromPresenceList = function(callback, userIds) {
-  let opts = {"drop": userIds};
+  const opts = {"drop": userIds};
   return _presenceList(callback, this, opts, "POST");
 };
 
@@ -1583,7 +1583,7 @@ MatrixClient.prototype.scrollback = function(room, limit, callback) {
     if (info.promise) {
         return info.promise;
     } else if (info.errorTs) {
-        let timeWaitedMs = Date.now() - info.errorTs;
+        const timeWaitedMs = Date.now() - info.errorTs;
         timeToWaitMs = Math.max(SCROLLBACK_DELAY_MS - timeWaitedMs, 0);
     }
 
@@ -1591,7 +1591,7 @@ MatrixClient.prototype.scrollback = function(room, limit, callback) {
         return q(room); // already at the start.
     }
     // attempt to grab more events from the store first
-    let numAdded = this.store.scrollback(room, limit).length;
+    const numAdded = this.store.scrollback(room, limit).length;
     if (numAdded === limit) {
         // store contained everything we needed.
         return q(room);
@@ -1599,26 +1599,26 @@ MatrixClient.prototype.scrollback = function(room, limit, callback) {
     // reduce the required number of events appropriately
     limit = limit - numAdded;
 
-    let path = utils.encodeUri(
+    const path = utils.encodeUri(
         "/rooms/$roomId/messages", {$roomId: room.roomId}
     );
-    let params = {
+    const params = {
         from: room.oldState.paginationToken,
         limit: limit,
         dir: 'b',
     };
-    let defer = q.defer();
+    const defer = q.defer();
     info = {
         promise: defer.promise,
         errorTs: null,
     };
-    let self = this;
+    const self = this;
     // wait for a time before doing this request
     // (which may be 0 in order not to special case the code paths)
     q.delay(timeToWaitMs).then(function() {
         return self._http.authedRequest(callback, "GET", path, params);
     }).done(function(res) {
-        let matrixEvents = utils.map(res.chunk, _PojoToMatrixEventMapper(self));
+        const matrixEvents = utils.map(res.chunk, _PojoToMatrixEventMapper(self));
         room.addEventsToTimeline(matrixEvents, true, room.getLiveTimeline());
         room.oldState.paginationToken = res.end;
         if (res.chunk.length === 0) {
@@ -1653,40 +1653,40 @@ MatrixClient.prototype.paginateEventContext = function(eventContext, opts) {
     // TODO: we should implement a backoff (as per scrollback()) to deal more
     // nicely with HTTP errors.
     opts = opts || {};
-    let backwards = opts.backwards || false;
+    const backwards = opts.backwards || false;
 
-    let token = eventContext.getPaginateToken(backwards);
+    const token = eventContext.getPaginateToken(backwards);
     if (!token) {
         // no more results.
         return q.reject(new Error("No paginate token"));
     }
 
-    let dir = backwards ? 'b' : 'f';
-    let pendingRequest = eventContext._paginateRequests[dir];
+    const dir = backwards ? 'b' : 'f';
+    const pendingRequest = eventContext._paginateRequests[dir];
 
     if (pendingRequest) {
         // already a request in progress - return the existing promise
         return pendingRequest;
     }
 
-    let path = utils.encodeUri(
+    const path = utils.encodeUri(
         "/rooms/$roomId/messages", {$roomId: eventContext.getEvent().getRoomId()}
     );
-    let params = {
+    const params = {
         from: token,
         limit: ('limit' in opts) ? opts.limit : 30,
         dir: dir,
     };
 
-    let self = this;
-    let promise =
+    const self = this;
+    const promise =
         self._http.authedRequest(undefined, "GET", path, params
     ).then(function(res) {
         let token = res.end;
         if (res.chunk.length === 0) {
             token = null;
         } else {
-            let matrixEvents = utils.map(res.chunk, self.getEventMapper());
+            const matrixEvents = utils.map(res.chunk, self.getEventMapper());
             if (backwards) {
                 // eventContext expects the events in timeline order, but
                 // back-pagination returns them in reverse order.
@@ -1730,7 +1730,7 @@ MatrixClient.prototype.getEventTimeline = function(timelineSet, eventId) {
         return q(timelineSet.getTimelineForEvent(eventId));
     }
 
-    let path = utils.encodeUri(
+    const path = utils.encodeUri(
         "/rooms/$roomId/context/$eventId", {
             $roomId: timelineSet.room.roomId,
             $eventId: eventId,
@@ -1739,8 +1739,8 @@ MatrixClient.prototype.getEventTimeline = function(timelineSet, eventId) {
 
     // TODO: we should implement a backoff (as per scrollback()) to deal more
     // nicely with HTTP errors.
-    let self = this;
-    let promise =
+    const self = this;
+    const promise =
         self._http.authedRequest(undefined, "GET", path
     ).then(function(res) {
         if (!res.event) {
@@ -1757,10 +1757,10 @@ MatrixClient.prototype.getEventTimeline = function(timelineSet, eventId) {
         // have known state.
         // events_after is already backwards; events_before is forwards.
         res.events_after.reverse();
-        let events = res.events_after
+        const events = res.events_after
             .concat([res.event])
             .concat(res.events_before);
-        let matrixEvents = utils.map(events, self.getEventMapper());
+        const matrixEvents = utils.map(events, self.getEventMapper());
 
         let timeline = timelineSet.getTimelineForEvent(matrixEvents[0].getId());
         if (!timeline) {
@@ -1776,7 +1776,7 @@ MatrixClient.prototype.getEventTimeline = function(timelineSet, eventId) {
         // room's index again. On the other hand, there's no guarantee the
         // event ended up anywhere, if it was later redacted, so we just
         // return the timeline we first thought of.
-        let tl = timelineSet.getTimelineForEvent(eventId) || timeline;
+        const tl = timelineSet.getTimelineForEvent(eventId) || timeline;
         return tl;
     });
     return promise;
@@ -1797,12 +1797,12 @@ MatrixClient.prototype.getEventTimeline = function(timelineSet, eventId) {
  *    events and we reached either end of the timeline; else true.
  */
 MatrixClient.prototype.paginateEventTimeline = function(eventTimeline, opts) {
-    let isNotifTimeline = (eventTimeline.getTimelineSet() === this._notifTimelineSet);
+    const isNotifTimeline = (eventTimeline.getTimelineSet() === this._notifTimelineSet);
 
     // TODO: we should implement a backoff (as per scrollback()) to deal more
     // nicely with HTTP errors.
     opts = opts || {};
-    let backwards = opts.backwards || false;
+    const backwards = opts.backwards || false;
 
     if (isNotifTimeline) {
         if (!backwards) {
@@ -1810,15 +1810,15 @@ MatrixClient.prototype.paginateEventTimeline = function(eventTimeline, opts) {
         }
     }
 
-    let dir = backwards ? EventTimeline.BACKWARDS : EventTimeline.FORWARDS;
+    const dir = backwards ? EventTimeline.BACKWARDS : EventTimeline.FORWARDS;
 
-    let token = eventTimeline.getPaginationToken(dir);
+    const token = eventTimeline.getPaginationToken(dir);
     if (!token) {
         // no token - no results.
         return q(false);
     }
 
-    let pendingRequest = eventTimeline._paginationRequests[dir];
+    const pendingRequest = eventTimeline._paginationRequests[dir];
 
     if (pendingRequest) {
         // already a request in progress - return the existing promise
@@ -1826,7 +1826,7 @@ MatrixClient.prototype.paginateEventTimeline = function(eventTimeline, opts) {
     }
 
     let path, params, promise;
-    let self = this;
+    const self = this;
 
     if (isNotifTimeline) {
         path = "/notifications";
@@ -1843,12 +1843,12 @@ MatrixClient.prototype.paginateEventTimeline = function(eventTimeline, opts) {
             this._http.authedRequestWithPrefix(undefined, "GET", path, params,
                 undefined, httpApi.PREFIX_UNSTABLE
         ).then(function(res) {
-            let token = res.next_token;
-            let matrixEvents = [];
+            const token = res.next_token;
+            const matrixEvents = [];
 
             for (let i = 0; i < res.notifications.length; i++) {
-                let notification = res.notifications[i];
-                let event = self.getEventMapper()(notification.event);
+                const notification = res.notifications[i];
+                const event = self.getEventMapper()(notification.event);
                 event.setPushActions(
                     PushProcessor.actionListToActionsObject(notification.actions)
                 );
@@ -1871,7 +1871,7 @@ MatrixClient.prototype.paginateEventTimeline = function(eventTimeline, opts) {
         });
         eventTimeline._paginationRequests[dir] = promise;
     } else {
-        let room = this.getRoom(eventTimeline.getRoomId());
+        const room = this.getRoom(eventTimeline.getRoomId());
         if (!room) {
             throw new Error("Unknown room " + eventTimeline.getRoomId());
         }
@@ -1885,7 +1885,7 @@ MatrixClient.prototype.paginateEventTimeline = function(eventTimeline, opts) {
             dir: dir,
         };
 
-        let filter = eventTimeline.getFilter();
+        const filter = eventTimeline.getFilter();
         if (filter) {
             // XXX: it's horrific that /messages' filter parameter doesn't match
             // /sync's one - see https://matrix.org/jira/browse/SPEC-451
@@ -1895,8 +1895,8 @@ MatrixClient.prototype.paginateEventTimeline = function(eventTimeline, opts) {
         promise =
             this._http.authedRequest(undefined, "GET", path, params
         ).then(function(res) {
-            let token = res.end;
-            let matrixEvents = utils.map(res.chunk, self.getEventMapper());
+            const token = res.end;
+            const matrixEvents = utils.map(res.chunk, self.getEventMapper());
             eventTimeline.getTimelineSet()
                 .addEventsToTimeline(matrixEvents, backwards, eventTimeline, token);
 
@@ -1988,7 +1988,7 @@ MatrixClient.prototype.stopPeeking = function() {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.setGuestAccess = function(roomId, opts) {
-    let writePromise = this.sendStateEvent(roomId, "m.room.guest_access", {
+    const writePromise = this.sendStateEvent(roomId, "m.room.guest_access", {
         guest_access: opts.allowJoin ? "can_join" : "forbidden",
     });
 
@@ -2103,12 +2103,12 @@ MatrixClient.prototype.requestPasswordEmailToken = function(email, clientSecret,
 MatrixClient.prototype._requestTokenFromEndpoint = function(endpoint,
                                                     email, clientSecret,
                                                     sendAttempt, nextLink, callback) {
-    let id_server_url = url.parse(this.idBaseUrl);
+    const id_server_url = url.parse(this.idBaseUrl);
     if (id_server_url.host === null) {
         throw new Error("Invalid ID server URL: " + this.idBaseUrl);
     }
 
-    let params = {
+    const params = {
         client_secret: clientSecret,
         email: email,
         send_attempt: sendAttempt,
@@ -2136,7 +2136,7 @@ MatrixClient.prototype.getRoomPushRule = function(scope, roomId) {
     // and its id is the room id.
     if (this.pushRules) {
         for (let i = 0; i < this.pushRules[scope].room.length; i++) {
-            let rule = this.pushRules[scope].room[i];
+            const rule = this.pushRules[scope].room[i];
             if (rule.rule_id === roomId) {
                 return rule;
             }
@@ -2158,11 +2158,11 @@ MatrixClient.prototype.getRoomPushRule = function(scope, roomId) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.setRoomMutePushRule = function(scope, roomId, mute) {
-    let self = this;
+    const self = this;
     let deferred, hasDontNotifyRule;
 
     // Get the existing room-kind push rule if any
-    let roomPushRule = this.getRoomPushRule(scope, roomId);
+    const roomPushRule = this.getRoomPushRule(scope, roomId);
     if (roomPushRule) {
         if (0 <= roomPushRule.actions.indexOf("dont_notify")) {
             hasDontNotifyRule = true;
@@ -2202,7 +2202,7 @@ MatrixClient.prototype.setRoomMutePushRule = function(scope, roomId, mute) {
 
     if (deferred) {
         // Update this.pushRules when the operation completes
-        let ruleRefreshDeferred = q.defer();
+        const ruleRefreshDeferred = q.defer();
         deferred.done(function() {
             self.getPushRules().done(function(result) {
                 self.pushRules = result;
@@ -2273,7 +2273,7 @@ MatrixClient.prototype.searchMessageText = function(opts, callback) {
 MatrixClient.prototype.searchRoomEvents = function(opts) {
     // TODO: support groups
 
-    let body = {
+    const body = {
         search_categories: {
             room_events: {
                 search_term: opts.term,
@@ -2288,7 +2288,7 @@ MatrixClient.prototype.searchRoomEvents = function(opts) {
         },
     };
 
-    let searchResults = {
+    const searchResults = {
         _query: body,
         results: [],
         highlights: [],
@@ -2319,12 +2319,12 @@ MatrixClient.prototype.backPaginateRoomEventsSearch = function(searchResults) {
         return searchResults.pendingRequest;
     }
 
-    let searchOpts = {
+    const searchOpts = {
         body: searchResults._query,
         next_batch: searchResults.next_batch,
     };
 
-    let promise = this.search(searchOpts).then(
+    const promise = this.search(searchOpts).then(
         this._processRoomEventsSearch.bind(this, searchResults)
     ).finally(function() {
         searchResults.pendingRequest = null;
@@ -2344,14 +2344,14 @@ MatrixClient.prototype.backPaginateRoomEventsSearch = function(searchResults) {
  * @private
  */
 MatrixClient.prototype._processRoomEventsSearch = function(searchResults, response) {
-    let room_events = response.search_categories.room_events;
+    const room_events = response.search_categories.room_events;
 
     searchResults.count = room_events.count;
     searchResults.next_batch = room_events.next_batch;
 
     // combine the highlight list with our existing list; build an object
     // to avoid O(N^2) fail
-    let highlights = {};
+    const highlights = {};
     room_events.highlights.forEach(function(hl) {
         highlights[hl] = 1;
     });
@@ -2364,7 +2364,7 @@ MatrixClient.prototype._processRoomEventsSearch = function(searchResults, respon
 
     // append the new results to our existing results
     for (let i = 0; i < room_events.results.length; i++) {
-        let sr = SearchResult.fromJson(room_events.results[i], this.getEventMapper());
+        const sr = SearchResult.fromJson(room_events.results[i], this.getEventMapper());
         searchResults.results.push(sr);
     }
     return searchResults;
@@ -2385,8 +2385,8 @@ MatrixClient.prototype.syncLeftRooms = function() {
     if (this._syncLeftRoomsPromise) {
         return this._syncLeftRoomsPromise; // return the ongoing request
     }
-    let self = this;
-    let syncApi = new SyncApi(this, this._clientOpts);
+    const self = this;
+    const syncApi = new SyncApi(this, this._clientOpts);
     this._syncLeftRoomsPromise = syncApi.syncLeftRooms();
 
     // cleanup locks
@@ -2410,15 +2410,15 @@ MatrixClient.prototype.syncLeftRooms = function() {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.createFilter = function(content) {
-    let self = this;
-    let path = utils.encodeUri("/user/$userId/filter", {
+    const self = this;
+    const path = utils.encodeUri("/user/$userId/filter", {
         $userId: this.credentials.userId,
     });
     return this._http.authedRequest(
         undefined, "POST", path, undefined, content
     ).then(function(response) {
         // persist the filter
-        let filter = Filter.fromJson(
+        const filter = Filter.fromJson(
             self.credentials.userId, response.filter_id, content
         );
         self.store.storeFilter(filter);
@@ -2437,14 +2437,14 @@ MatrixClient.prototype.createFilter = function(content) {
  */
 MatrixClient.prototype.getFilter = function(userId, filterId, allowCached) {
     if (allowCached) {
-        let filter = this.store.getFilter(userId, filterId);
+        const filter = this.store.getFilter(userId, filterId);
         if (filter) {
             return q(filter);
         }
     }
 
-    let self = this;
-    let path = utils.encodeUri("/user/$userId/filter/$filterId", {
+    const self = this;
+    const path = utils.encodeUri("/user/$userId/filter/$filterId", {
         $userId: userId,
         $filterId: filterId,
     });
@@ -2453,7 +2453,7 @@ MatrixClient.prototype.getFilter = function(userId, filterId, allowCached) {
         undefined, "GET", path, undefined, undefined
     ).then(function(response) {
         // persist the filter
-        let filter = Filter.fromJson(
+        const filter = Filter.fromJson(
             userId, filterId, response
         );
         self.store.storeFilter(filter);
@@ -2467,17 +2467,17 @@ MatrixClient.prototype.getFilter = function(userId, filterId, allowCached) {
  * @return {Promise<String>} Filter ID
  */
 MatrixClient.prototype.getOrCreateFilter = function(filterName, filter) {
-    let filterId = this.store.getFilterIdByName(filterName);
+    const filterId = this.store.getFilterIdByName(filterName);
     let promise = q();
-    let self = this;
+    const self = this;
 
     if (filterId) {
         // check that the existing filter matches our expectations
         promise = self.getFilter(self.credentials.userId,
                          filterId, true
         ).then(function(existingFilter) {
-            let oldDef = existingFilter.getDefinition();
-            let newDef = filter.getDefinition();
+            const oldDef = existingFilter.getDefinition();
+            const newDef = filter.getDefinition();
 
             if (utils.deepCompare(oldDef, newDef)) {
                 // super, just use that.
@@ -2535,7 +2535,7 @@ MatrixClient.prototype.getOrCreateFilter = function(filterName, filter) {
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.getOpenIdToken = function() {
-    let path = utils.encodeUri("/user/$userId/openid/request_token", {
+    const path = utils.encodeUri("/user/$userId/openid/request_token", {
         $userId: this.credentials.userId,
     });
 
@@ -2624,8 +2624,8 @@ MatrixClient.prototype.startClient = function(opts) {
 
     if (this._crypto) {
         this._crypto.uploadKeys(5).done();
-        let tenMinutes = 1000 * 60 * 10;
-        let self = this;
+        const tenMinutes = 1000 * 60 * 10;
+        const self = this;
         this._uploadIntervalID = global.setInterval(function() {
             self._crypto.uploadKeys(5).done();
         }, tenMinutes);
@@ -2661,7 +2661,7 @@ MatrixClient.prototype.stopClient = function() {
 };
 
 function setupCallEventHandler(client) {
-    let candidatesByCall = {
+    const candidatesByCall = {
         // callId: [Candidate]
     };
 
@@ -2674,11 +2674,11 @@ function setupCallEventHandler(client) {
     client.on("sync", function(state) {
         if (state === "PREPARED") {
             isClientPrepared = true;
-            let ignoreCallIds = {}; // Set<String>
+            const ignoreCallIds = {}; // Set<String>
             // inspect the buffer and mark all calls which have been answered
             // or hung up before passing them to the call event handler.
             for (let i = callEventBuffer.length - 1; i >= 0; i--) {
-                let ev = callEventBuffer[i];
+                const ev = callEventBuffer[i];
                 if (ev.getType() === "m.call.answer" ||
                         ev.getType() === "m.call.hangup") {
                     ignoreCallIds[ev.getContent().call_id] = "yep";
@@ -2709,7 +2709,7 @@ function setupCallEventHandler(client) {
         if (event.getType().indexOf("m.call.") !== 0) {
             return; // not a call event
         }
-        let content = event.getContent();
+        const content = event.getContent();
         let call = content.call_id ? client.callList[content.call_id] : undefined;
         let i;
         //console.log("RECV %s content=%s", event.getType(), JSON.stringify(content));
@@ -2761,9 +2761,9 @@ function setupCallEventHandler(client) {
 
             // Were we trying to call that user (room)?
             let existingCall;
-            let existingCalls = utils.values(client.callList);
+            const existingCalls = utils.values(client.callList);
             for (i = 0; i < existingCalls.length; ++i) {
-                let thisCall = existingCalls[i];
+                const thisCall = existingCalls[i];
                 if (call.room_id === thisCall.room_id &&
                         thisCall.direction === 'outbound' &&
                         (["wait_local_media", "create_offer", "invite_sent"].indexOf(
@@ -2862,7 +2862,7 @@ function checkTurnServers(client) {
                 res.ttl + " secs");
             // map the response to a format that can be fed to
             // RTCPeerConnection
-            let servers = {
+            const servers = {
                 urls: res.uris,
                 username: res.username,
                 credential: res.password,
@@ -2898,7 +2898,7 @@ function _resolve(callback, defer, res) {
 
 function _PojoToMatrixEventMapper(client) {
     function mapper(plainOldJsObject) {
-        let event = new MatrixEvent(plainOldJsObject);
+        const event = new MatrixEvent(plainOldJsObject);
         if (event.isEncrypted()) {
             _decryptEvent(client, event);
         }
@@ -2924,7 +2924,7 @@ MatrixClient.prototype.getEventMapper = function() {
  */
 MatrixClient.prototype.generateClientSecret = function() {
     let ret = "";
-    let chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+    const chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
 
     for (let i = 0; i < 32; i++) {
         ret += chars.charAt(Math.floor(Math.random() * chars.length));
diff --git a/src/content-repo.js b/src/content-repo.js
index 124e4ca27..185dad3d0 100644
--- a/src/content-repo.js
+++ b/src/content-repo.js
@@ -16,7 +16,7 @@ limitations under the License.
 /**
  * @module content-repo
  */
-let utils = require("./utils");
+const utils = require("./utils");
 
 /** Content Repo utility functions */
 module.exports = {
@@ -48,7 +48,7 @@ module.exports = {
         }
         let serverAndMediaId = mxc.slice(6); // strips mxc://
         let prefix = "/_matrix/media/v1/download/";
-        let params = {};
+        const params = {};
 
         if (width) {
             params.width = width;
@@ -94,12 +94,12 @@ module.exports = {
         if (!height) {
             height = 96;
         }
-        let params = {
+        const params = {
             width: width,
             height: height,
         };
 
-        let path = utils.encodeUri("/_matrix/media/v1/identicon/$ident", {
+        const path = utils.encodeUri("/_matrix/media/v1/identicon/$ident", {
             $ident: identiconString,
         });
         return baseUrl + path +
diff --git a/src/crypto/OlmDevice.js b/src/crypto/OlmDevice.js
index 72199c940..aaa3cb750 100644
--- a/src/crypto/OlmDevice.js
+++ b/src/crypto/OlmDevice.js
@@ -20,13 +20,13 @@ limitations under the License.
  *
  * @module crypto/OlmDevice
  */
-let Olm = require("olm");
-let utils = require("../utils");
+const Olm = require("olm");
+const utils = require("../utils");
 
 
 // The maximum size of an event is 65K, and we base64 the content, so this is a
 // reasonable approximation to the biggest plaintext we can encrypt.
-let MAX_PLAINTEXT_LENGTH = 65536 * 3 / 4;
+const MAX_PLAINTEXT_LENGTH = 65536 * 3 / 4;
 
 function checkPayloadLength(payloadString) {
     if (payloadString === undefined) {
@@ -79,7 +79,7 @@ function OlmDevice(sessionStore) {
     this._pickleKey = "DEFAULT_KEY";
 
     let e2eKeys;
-    let account = new Olm.Account();
+    const account = new Olm.Account();
     try {
         _initialise_account(this._sessionStore, this._pickleKey, account);
         e2eKeys = JSON.parse(account.identity_keys());
@@ -108,14 +108,14 @@ function OlmDevice(sessionStore) {
 }
 
 function _initialise_account(sessionStore, pickleKey, account) {
-    let e2eAccount = sessionStore.getEndToEndAccount();
+    const e2eAccount = sessionStore.getEndToEndAccount();
     if (e2eAccount !== null) {
         account.unpickle(pickleKey, e2eAccount);
         return;
     }
 
     account.create();
-    let pickled = account.pickle(pickleKey);
+    const pickled = account.pickle(pickleKey);
     sessionStore.storeEndToEndAccount(pickled);
 }
 
@@ -135,9 +135,9 @@ OlmDevice.getOlmVersion = function() {
  * @private
  */
 OlmDevice.prototype._getAccount = function(func) {
-    let account = new Olm.Account();
+    const account = new Olm.Account();
     try {
-        let pickledAccount = this._sessionStore.getEndToEndAccount();
+        const pickledAccount = this._sessionStore.getEndToEndAccount();
         account.unpickle(this._pickleKey, pickledAccount);
         return func(account);
     } finally {
@@ -153,7 +153,7 @@ OlmDevice.prototype._getAccount = function(func) {
  * @private
  */
 OlmDevice.prototype._saveAccount = function(account) {
-    let pickledAccount = account.pickle(this._pickleKey);
+    const pickledAccount = account.pickle(this._pickleKey);
     this._sessionStore.storeEndToEndAccount(pickledAccount);
 };
 
@@ -168,10 +168,10 @@ OlmDevice.prototype._saveAccount = function(account) {
  * @private
  */
 OlmDevice.prototype._getSession = function(deviceKey, sessionId, func) {
-    let sessions = this._sessionStore.getEndToEndSessions(deviceKey);
-    let pickledSession = sessions[sessionId];
+    const sessions = this._sessionStore.getEndToEndSessions(deviceKey);
+    const pickledSession = sessions[sessionId];
 
-    let session = new Olm.Session();
+    const session = new Olm.Session();
     try {
         session.unpickle(this._pickleKey, pickledSession);
         return func(session);
@@ -189,7 +189,7 @@ OlmDevice.prototype._getSession = function(deviceKey, sessionId, func) {
  * @private
  */
 OlmDevice.prototype._saveSession = function(deviceKey, session) {
-    let pickledSession = session.pickle(this._pickleKey);
+    const pickledSession = session.pickle(this._pickleKey);
     this._sessionStore.storeEndToEndSession(
         deviceKey, session.session_id(), pickledSession
     );
@@ -204,7 +204,7 @@ OlmDevice.prototype._saveSession = function(deviceKey, session) {
  * @private
  */
 OlmDevice.prototype._getUtility = function(func) {
-    let utility = new Olm.Utility();
+    const utility = new Olm.Utility();
     try {
         return func(utility);
     } finally {
@@ -254,7 +254,7 @@ OlmDevice.prototype.maxNumberOfOneTimeKeys = function() {
  * Marks all of the one-time keys as published.
  */
 OlmDevice.prototype.markKeysAsPublished = function() {
-    let self = this;
+    const self = this;
     this._getAccount(function(account) {
         account.mark_keys_as_published();
         self._saveAccount(account);
@@ -267,7 +267,7 @@ OlmDevice.prototype.markKeysAsPublished = function() {
  * @param {number} numKeys number of keys to generate
  */
 OlmDevice.prototype.generateOneTimeKeys = function(numKeys) {
-    let self = this;
+    const self = this;
     this._getAccount(function(account) {
         account.generate_one_time_keys(numKeys);
         self._saveAccount(account);
@@ -286,9 +286,9 @@ OlmDevice.prototype.generateOneTimeKeys = function(numKeys) {
 OlmDevice.prototype.createOutboundSession = function(
     theirIdentityKey, theirOneTimeKey
 ) {
-    let self = this;
+    const self = this;
     return this._getAccount(function(account) {
-        let session = new Olm.Session();
+        const session = new Olm.Session();
         try {
             session.create_outbound(account, theirIdentityKey, theirOneTimeKey);
             self._saveSession(theirIdentityKey, session);
@@ -320,15 +320,15 @@ OlmDevice.prototype.createInboundSession = function(
         throw new Error("Need message_type == 0 to create inbound session");
     }
 
-    let self = this;
+    const self = this;
     return this._getAccount(function(account) {
-        let session = new Olm.Session();
+        const session = new Olm.Session();
         try {
             session.create_inbound_from(account, theirDeviceIdentityKey, ciphertext);
             account.remove_one_time_keys(session);
             self._saveAccount(account);
 
-            let payloadString = session.decrypt(message_type, ciphertext);
+            const payloadString = session.decrypt(message_type, ciphertext);
 
             self._saveSession(theirDeviceIdentityKey, session);
 
@@ -351,7 +351,7 @@ OlmDevice.prototype.createInboundSession = function(
  * @return {string[]}  a list of known session ids for the device
  */
 OlmDevice.prototype.getSessionIdsForDevice = function(theirDeviceIdentityKey) {
-    let sessions = this._sessionStore.getEndToEndSessions(
+    const sessions = this._sessionStore.getEndToEndSessions(
         theirDeviceIdentityKey
     );
     return utils.keys(sessions);
@@ -365,7 +365,7 @@ OlmDevice.prototype.getSessionIdsForDevice = function(theirDeviceIdentityKey) {
  * @return {string?}  session id, or null if no established session
  */
 OlmDevice.prototype.getSessionIdForDevice = function(theirDeviceIdentityKey) {
-    let sessionIds = this.getSessionIdsForDevice(theirDeviceIdentityKey);
+    const sessionIds = this.getSessionIdsForDevice(theirDeviceIdentityKey);
     if (sessionIds.length === 0) {
         return null;
     }
@@ -386,10 +386,10 @@ OlmDevice.prototype.getSessionIdForDevice = function(theirDeviceIdentityKey) {
  * @return {Array.<{sessionId: string, hasReceivedMessage: Boolean}>}
  */
 OlmDevice.prototype.getSessionInfoForDevice = function(deviceIdentityKey) {
-    let sessionIds = this.getSessionIdsForDevice(deviceIdentityKey);
+    const sessionIds = this.getSessionIdsForDevice(deviceIdentityKey);
     sessionIds.sort();
 
-    let info = [];
+    const info = [];
 
     function getSessionInfo(session) {
         return {
@@ -398,8 +398,8 @@ OlmDevice.prototype.getSessionInfoForDevice = function(deviceIdentityKey) {
     }
 
     for (let i = 0; i < sessionIds.length; i++) {
-        let sessionId = sessionIds[i];
-        let res = this._getSession(deviceIdentityKey, sessionId, getSessionInfo);
+        const sessionId = sessionIds[i];
+        const res = this._getSession(deviceIdentityKey, sessionId, getSessionInfo);
         res.sessionId = sessionId;
         info.push(res);
     }
@@ -419,12 +419,12 @@ OlmDevice.prototype.getSessionInfoForDevice = function(deviceIdentityKey) {
 OlmDevice.prototype.encryptMessage = function(
     theirDeviceIdentityKey, sessionId, payloadString
 ) {
-    let self = this;
+    const self = this;
 
     checkPayloadLength(payloadString);
 
     return this._getSession(theirDeviceIdentityKey, sessionId, function(session) {
-        let res = session.encrypt(payloadString);
+        const res = session.encrypt(payloadString);
         self._saveSession(theirDeviceIdentityKey, session);
         return res;
     });
@@ -444,10 +444,10 @@ OlmDevice.prototype.encryptMessage = function(
 OlmDevice.prototype.decryptMessage = function(
     theirDeviceIdentityKey, sessionId, message_type, ciphertext
 ) {
-    let self = this;
+    const self = this;
 
     return this._getSession(theirDeviceIdentityKey, sessionId, function(session) {
-        let payloadString = session.decrypt(message_type, ciphertext);
+        const payloadString = session.decrypt(message_type, ciphertext);
         self._saveSession(theirDeviceIdentityKey, session);
 
         return payloadString;
@@ -489,7 +489,7 @@ OlmDevice.prototype.matchesSession = function(
  * @private
  */
 OlmDevice.prototype._saveOutboundGroupSession = function(session) {
-    let pickledSession = session.pickle(this._pickleKey);
+    const pickledSession = session.pickle(this._pickleKey);
     this._outboundGroupSessionStore[session.session_id()] = pickledSession;
 };
 
@@ -504,12 +504,12 @@ OlmDevice.prototype._saveOutboundGroupSession = function(session) {
  * @private
  */
 OlmDevice.prototype._getOutboundGroupSession = function(sessionId, func) {
-    let pickled = this._outboundGroupSessionStore[sessionId];
+    const pickled = this._outboundGroupSessionStore[sessionId];
     if (pickled === null) {
         throw new Error("Unknown outbound group session " + sessionId);
     }
 
-    let session = new Olm.OutboundGroupSession();
+    const session = new Olm.OutboundGroupSession();
     try {
         session.unpickle(this._pickleKey, pickled);
         return func(session);
@@ -525,7 +525,7 @@ OlmDevice.prototype._getOutboundGroupSession = function(sessionId, func) {
  * @return {string} sessionId for the outbound session.
  */
 OlmDevice.prototype.createOutboundGroupSession = function() {
-    let session = new Olm.OutboundGroupSession();
+    const session = new Olm.OutboundGroupSession();
     try {
         session.create();
         this._saveOutboundGroupSession(session);
@@ -545,12 +545,12 @@ OlmDevice.prototype.createOutboundGroupSession = function() {
  * @return {string} ciphertext
  */
 OlmDevice.prototype.encryptGroupMessage = function(sessionId, payloadString) {
-    let self = this;
+    const self = this;
 
     checkPayloadLength(payloadString);
 
     return this._getOutboundGroupSession(sessionId, function(session) {
-        let res = session.encrypt(payloadString);
+        const res = session.encrypt(payloadString);
         self._saveOutboundGroupSession(session);
         return res;
     });
@@ -590,7 +590,7 @@ OlmDevice.prototype.getOutboundGroupSessionKey = function(sessionId) {
 OlmDevice.prototype._saveInboundGroupSession = function(
     roomId, senderCurve25519Key, sessionId, session, keysClaimed
 ) {
-    let r = {
+    const r = {
         room_id: roomId,
         session: session.pickle(this._pickleKey),
         keysClaimed: keysClaimed,
@@ -639,7 +639,7 @@ OlmDevice.prototype._getInboundGroupSession = function(
         );
     }
 
-    let session = new Olm.InboundGroupSession();
+    const session = new Olm.InboundGroupSession();
     try {
         session.unpickle(this._pickleKey, r.session);
         return func(session, r.keysClaimed || {});
@@ -660,7 +660,7 @@ OlmDevice.prototype._getInboundGroupSession = function(
 OlmDevice.prototype.addInboundGroupSession = function(
     roomId, senderKey, sessionId, sessionKey, keysClaimed
 ) {
-    let self = this;
+    const self = this;
 
     /* if we already have this session, consider updating it */
     function updateSession(session) {
@@ -670,7 +670,7 @@ OlmDevice.prototype.addInboundGroupSession = function(
         return true;
     }
 
-    let r = this._getInboundGroupSession(
+    const r = this._getInboundGroupSession(
         roomId, senderKey, sessionId, updateSession
     );
 
@@ -679,7 +679,7 @@ OlmDevice.prototype.addInboundGroupSession = function(
     }
 
     // new session.
-    let session = new Olm.InboundGroupSession();
+    const session = new Olm.InboundGroupSession();
     try {
         session.create(sessionKey);
         if (sessionId != session.session_id()) {
@@ -753,10 +753,10 @@ OlmDevice.prototype.importInboundGroupSession = function(data) {
 OlmDevice.prototype.decryptGroupMessage = function(
     roomId, senderKey, sessionId, body
 ) {
-    let self = this;
+    const self = this;
 
     function decrypt(session, keysClaimed) {
-        let res = session.decrypt(body);
+        const res = session.decrypt(body);
 
         let plaintext = res.plaintext;
         if (plaintext === undefined) {
@@ -764,7 +764,7 @@ OlmDevice.prototype.decryptGroupMessage = function(
             plaintext = res;
         } else {
             // Check if we have seen this message index before to detect replay attacks.
-            let messageIndexKey = senderKey + "|" + sessionId + "|" + res.message_index;
+            const messageIndexKey = senderKey + "|" + sessionId + "|" + res.message_index;
             if (messageIndexKey in self._inboundGroupSessionMessageIndexes) {
                 throw new Error(
                     "Duplicate message index, possible replay attack: " +
@@ -776,7 +776,7 @@ OlmDevice.prototype.decryptGroupMessage = function(
 
         // the sender must have had the senderKey to persuade us to save the
         // session.
-        let keysProved = {curve25519: senderKey};
+        const keysProved = {curve25519: senderKey};
 
         self._saveInboundGroupSession(
             roomId, senderKey, sessionId, session, keysClaimed
diff --git a/src/crypto/algorithms/base.js b/src/crypto/algorithms/base.js
index 7973231a7..10a4ce02f 100644
--- a/src/crypto/algorithms/base.js
+++ b/src/crypto/algorithms/base.js
@@ -20,7 +20,7 @@ limitations under the License.
  *
  * @module crypto/algorithms/base
  */
-let utils = require("../../utils");
+const utils = require("../../utils");
 
 /**
  * map of registered encryption algorithm classes. A map from string to {@link
@@ -53,7 +53,7 @@ module.exports.DECRYPTION_CLASSES = {};
  * @param {string} params.roomId  The ID of the room we will be sending to
  * @param {object} params.config  The body of the m.room.encryption event
  */
-let EncryptionAlgorithm = function(params) {
+const EncryptionAlgorithm = function(params) {
     this._userId = params.userId;
     this._deviceId = params.deviceId;
     this._crypto = params.crypto;
@@ -101,7 +101,7 @@ EncryptionAlgorithm.prototype.onRoomMembership = function(
  * @param {string=} params.roomId The ID of the room we will be receiving
  *     from. Null for to-device events.
  */
-let DecryptionAlgorithm = function(params) {
+const DecryptionAlgorithm = function(params) {
     this._userId = params.userId;
     this._crypto = params.crypto;
     this._olmDevice = params.olmDevice;
diff --git a/src/crypto/algorithms/index.js b/src/crypto/algorithms/index.js
index 532b2f205..ce64b3b11 100644
--- a/src/crypto/algorithms/index.js
+++ b/src/crypto/algorithms/index.js
@@ -19,7 +19,7 @@ limitations under the License.
  * @module crypto/algorithms
  */
 
-let base = require("./base");
+const base = require("./base");
 
 require("./olm");
 require("./megolm");
diff --git a/src/crypto/algorithms/megolm.js b/src/crypto/algorithms/megolm.js
index 5462e1c29..c645d5a09 100644
--- a/src/crypto/algorithms/megolm.js
+++ b/src/crypto/algorithms/megolm.js
@@ -21,11 +21,11 @@ limitations under the License.
  * @module crypto/algorithms/megolm
  */
 
-let q = require("q");
+const q = require("q");
 
-let utils = require("../../utils");
-let olmlib = require("../olmlib");
-let base = require("./base");
+const utils = require("../../utils");
+const olmlib = require("../olmlib");
+const base = require("./base");
 
 /**
  * @private
@@ -59,7 +59,7 @@ function OutboundSessionInfo(sessionId) {
 OutboundSessionInfo.prototype.needsRotation = function(
     rotationPeriodMsgs, rotationPeriodMs
 ) {
-    let sessionLifetime = new Date().getTime() - this.creationTime;
+    const sessionLifetime = new Date().getTime() - this.creationTime;
 
     if (this.useCount >= rotationPeriodMsgs ||
         sessionLifetime >= rotationPeriodMs
@@ -88,7 +88,7 @@ OutboundSessionInfo.prototype.needsRotation = function(
 OutboundSessionInfo.prototype.sharedWithTooManyDevices = function(
     devicesInRoom
 ) {
-    for (let userId in this.sharedWithDevices) {
+    for (const userId in this.sharedWithDevices) {
         if (!this.sharedWithDevices.hasOwnProperty(userId)) {
             continue;
         }
@@ -98,7 +98,7 @@ OutboundSessionInfo.prototype.sharedWithTooManyDevices = function(
             return true;
         }
 
-        for (let deviceId in this.sharedWithDevices[userId]) {
+        for (const deviceId in this.sharedWithDevices[userId]) {
             if (!this.sharedWithDevices[userId].hasOwnProperty(deviceId)) {
                 continue;
             }
@@ -157,7 +157,7 @@ utils.inherits(MegolmEncryption, base.EncryptionAlgorithm);
  *    OutboundSessionInfo when setup is complete.
  */
 MegolmEncryption.prototype._ensureOutboundSession = function(devicesInRoom) {
-    let self = this;
+    const self = this;
 
     let session;
 
@@ -187,23 +187,23 @@ MegolmEncryption.prototype._ensureOutboundSession = function(devicesInRoom) {
         }
 
         // now check if we need to share with any devices
-        let shareMap = {};
+        const shareMap = {};
 
-        for (let userId in devicesInRoom) {
+        for (const userId in devicesInRoom) {
             if (!devicesInRoom.hasOwnProperty(userId)) {
                 continue;
             }
 
-            let userDevices = devicesInRoom[userId];
+            const userDevices = devicesInRoom[userId];
 
-            for (let deviceId in userDevices) {
+            for (const deviceId in userDevices) {
                 if (!userDevices.hasOwnProperty(deviceId)) {
                     continue;
                 }
 
-                let deviceInfo = userDevices[deviceId];
+                const deviceInfo = userDevices[deviceId];
 
-                let key = deviceInfo.getIdentityKey();
+                const key = deviceInfo.getIdentityKey();
                 if (key == self._olmDevice.deviceCurve25519Key) {
                     // don't bother sending to ourself
                     continue;
@@ -230,7 +230,7 @@ MegolmEncryption.prototype._ensureOutboundSession = function(devicesInRoom) {
     }
 
     // first wait for the previous share to complete
-    let prom = this._setupPromise.then(prepareSession);
+    const prom = this._setupPromise.then(prepareSession);
 
     // _setupPromise resolves to `session` whether or not the share succeeds
     this._setupPromise = prom.then(returnSession, returnSession);
@@ -245,8 +245,8 @@ MegolmEncryption.prototype._ensureOutboundSession = function(devicesInRoom) {
  * @return {module:crypto/algorithms/megolm.OutboundSessionInfo} session
  */
 MegolmEncryption.prototype._prepareNewSession = function() {
-    let session_id = this._olmDevice.createOutboundGroupSession();
-    let key = this._olmDevice.getOutboundGroupSessionKey(session_id);
+    const session_id = this._olmDevice.createOutboundGroupSession();
+    const key = this._olmDevice.getOutboundGroupSessionKey(session_id);
 
     this._olmDevice.addInboundGroupSession(
         this._roomId, this._olmDevice.deviceCurve25519Key, session_id,
@@ -268,10 +268,10 @@ MegolmEncryption.prototype._prepareNewSession = function() {
  *     message has been sent.
  */
 MegolmEncryption.prototype._shareKeyWithDevices = function(session, devicesByUser) {
-    let self = this;
+    const self = this;
 
-    let key = this._olmDevice.getOutboundGroupSessionKey(session.sessionId);
-    let payload = {
+    const key = this._olmDevice.getOutboundGroupSessionKey(session.sessionId);
+    const payload = {
         type: "m.room_key",
         content: {
             algorithm: olmlib.MEGOLM_ALGORITHM,
@@ -282,26 +282,26 @@ MegolmEncryption.prototype._shareKeyWithDevices = function(session, devicesByUse
         },
     };
 
-    let contentMap = {};
+    const contentMap = {};
 
     return olmlib.ensureOlmSessionsForDevices(
         this._olmDevice, this._baseApis, devicesByUser
     ).then(function(devicemap) {
         let haveTargets = false;
 
-        for (let userId in devicesByUser) {
+        for (const userId in devicesByUser) {
             if (!devicesByUser.hasOwnProperty(userId)) {
                 continue;
             }
 
-            let devicesToShareWith = devicesByUser[userId];
-            let sessionResults = devicemap[userId];
+            const devicesToShareWith = devicesByUser[userId];
+            const sessionResults = devicemap[userId];
 
             for (let i = 0; i < devicesToShareWith.length; i++) {
-                let deviceInfo = devicesToShareWith[i];
-                let deviceId = deviceInfo.deviceId;
+                const deviceInfo = devicesToShareWith[i];
+                const deviceId = deviceInfo.deviceId;
 
-                let sessionResult = sessionResults[deviceId];
+                const sessionResult = sessionResults[deviceId];
                 if (!sessionResult.sessionId) {
                     // no session with this device, probably because there
                     // were no one-time keys.
@@ -321,7 +321,7 @@ MegolmEncryption.prototype._shareKeyWithDevices = function(session, devicesByUse
                     "sharing keys with device " + userId + ":" + deviceId
                 );
 
-                let encryptedContent = {
+                const encryptedContent = {
                     algorithm: olmlib.OLM_ALGORITHM,
                     sender_key: self._olmDevice.deviceCurve25519Key,
                     ciphertext: {},
@@ -359,16 +359,16 @@ MegolmEncryption.prototype._shareKeyWithDevices = function(session, devicesByUse
         // attempted to share with) rather than the contentMap (those we did
         // share with), because we don't want to try to claim a one-time-key
         // for dead devices on every message.
-        for (let userId in devicesByUser) {
+        for (const userId in devicesByUser) {
             if (!devicesByUser.hasOwnProperty(userId)) {
                 continue;
             }
             if (!session.sharedWithDevices[userId]) {
                 session.sharedWithDevices[userId] = {};
             }
-            let devicesToShareWith = devicesByUser[userId];
+            const devicesToShareWith = devicesByUser[userId];
             for (let i = 0; i < devicesToShareWith.length; i++) {
-                let deviceInfo = devicesToShareWith[i];
+                const deviceInfo = devicesToShareWith[i];
                 session.sharedWithDevices[userId][deviceInfo.deviceId] =
                     key.chain_index;
             }
@@ -386,21 +386,21 @@ MegolmEncryption.prototype._shareKeyWithDevices = function(session, devicesByUse
  * @return {module:client.Promise} Promise which resolves to the new event body
  */
 MegolmEncryption.prototype.encryptMessage = function(room, eventType, content) {
-    let self = this;
+    const self = this;
     return this._getDevicesInRoom(room).then(function(devicesInRoom) {
         return self._ensureOutboundSession(devicesInRoom);
     }).then(function(session) {
-        let payloadJson = {
+        const payloadJson = {
             room_id: self._roomId,
             type: eventType,
             content: content,
         };
 
-        let ciphertext = self._olmDevice.encryptGroupMessage(
+        const ciphertext = self._olmDevice.encryptGroupMessage(
             session.sessionId, JSON.stringify(payloadJson)
         );
 
-        let encryptedContent = {
+        const encryptedContent = {
             algorithm: olmlib.MEGOLM_ALGORITHM,
             sender_key: self._olmDevice.deviceCurve25519Key,
             ciphertext: ciphertext,
@@ -425,7 +425,7 @@ MegolmEncryption.prototype.encryptMessage = function(room, eventType, content) {
  */
 MegolmEncryption.prototype._getDevicesInRoom = function(room) {
     // XXX what about rooms where invitees can see the content?
-    let roomMembers = utils.map(room.getJoinedMembers(), function(u) {
+    const roomMembers = utils.map(room.getJoinedMembers(), function(u) {
         return u.userId;
     });
 
@@ -435,13 +435,13 @@ MegolmEncryption.prototype._getDevicesInRoom = function(room) {
     // an m.new_device.
     return this._crypto.downloadKeys(roomMembers, false).then(function(devices) {
         // remove any blocked devices
-        for (let userId in devices) {
+        for (const userId in devices) {
             if (!devices.hasOwnProperty(userId)) {
                 continue;
             }
 
-            let userDevices = devices[userId];
-            for (let deviceId in userDevices) {
+            const userDevices = devices[userId];
+            for (const deviceId in userDevices) {
                 if (!userDevices.hasOwnProperty(deviceId)) {
                     continue;
                 }
@@ -482,7 +482,7 @@ utils.inherits(MegolmDecryption, base.DecryptionAlgorithm);
  *   problem decrypting the event
  */
 MegolmDecryption.prototype.decryptEvent = function(event) {
-    let content = event.getWireContent();
+    const content = event.getWireContent();
 
     if (!content.sender_key || !content.session_id ||
         !content.ciphertext
@@ -510,7 +510,7 @@ MegolmDecryption.prototype.decryptEvent = function(event) {
         );
     }
 
-    let payload = JSON.parse(res.result);
+    const payload = JSON.parse(res.result);
 
     // belt-and-braces check that the room id matches that indicated by the HS
     // (this is somewhat redundant, since the megolm session is scoped to the
@@ -534,8 +534,8 @@ MegolmDecryption.prototype.decryptEvent = function(event) {
  * @param {module:models/event.MatrixEvent} event
  */
 MegolmDecryption.prototype._addEventToPendingList = function(event) {
-    let content = event.getWireContent();
-    let k = content.sender_key + "|" + content.session_id;
+    const content = event.getWireContent();
+    const k = content.sender_key + "|" + content.session_id;
     if (!this._pendingEvents[k]) {
         this._pendingEvents[k] = [];
     }
@@ -549,7 +549,7 @@ MegolmDecryption.prototype._addEventToPendingList = function(event) {
  */
 MegolmDecryption.prototype.onRoomKeyEvent = function(event) {
     console.log("Adding key from ", event);
-    let content = event.getContent();
+    const content = event.getContent();
 
     if (!content.room_id ||
         !content.session_id ||
diff --git a/src/crypto/algorithms/olm.js b/src/crypto/algorithms/olm.js
index 7efa05c64..ec690afb4 100644
--- a/src/crypto/algorithms/olm.js
+++ b/src/crypto/algorithms/olm.js
@@ -20,15 +20,15 @@ limitations under the License.
  *
  * @module crypto/algorithms/olm
  */
-let q = require('q');
+const q = require('q');
 
-let utils = require("../../utils");
-let olmlib = require("../olmlib");
-let DeviceInfo = require("../deviceinfo");
-let DeviceVerification = DeviceInfo.DeviceVerification;
+const utils = require("../../utils");
+const olmlib = require("../olmlib");
+const DeviceInfo = require("../deviceinfo");
+const DeviceVerification = DeviceInfo.DeviceVerification;
 
 
-let base = require("./base");
+const base = require("./base");
 
 /**
  * Olm encryption implementation
@@ -63,7 +63,7 @@ OlmEncryption.prototype._ensureSession = function(roomMembers) {
         return q();
     }
 
-    let self = this;
+    const self = this;
     this._prepPromise = self._crypto.downloadKeys(roomMembers, true).then(function(res) {
         return self._crypto.ensureOlmSessionsForUsers(roomMembers);
     }).then(function() {
@@ -89,31 +89,31 @@ OlmEncryption.prototype.encryptMessage = function(room, eventType, content) {
     // TODO: there is a race condition here! What if a new user turns up
     // just as you are sending a secret message?
 
-    let users = utils.map(room.getJoinedMembers(), function(u) {
+    const users = utils.map(room.getJoinedMembers(), function(u) {
         return u.userId;
     });
 
-    let self = this;
+    const self = this;
     return this._ensureSession(users).then(function() {
-        let payloadFields = {
+        const payloadFields = {
             room_id: room.roomId,
             type: eventType,
             content: content,
         };
 
-        let encryptedContent = {
+        const encryptedContent = {
             algorithm: olmlib.OLM_ALGORITHM,
             sender_key: self._olmDevice.deviceCurve25519Key,
             ciphertext: {},
         };
 
         for (let i = 0; i < users.length; ++i) {
-            let userId = users[i];
-            let devices = self._crypto.getStoredDevicesForUser(userId);
+            const userId = users[i];
+            const devices = self._crypto.getStoredDevicesForUser(userId);
 
             for (let j = 0; j < devices.length; ++j) {
-                let deviceInfo = devices[j];
-                let key = deviceInfo.getIdentityKey();
+                const deviceInfo = devices[j];
+                const key = deviceInfo.getIdentityKey();
                 if (key == self._olmDevice.deviceCurve25519Key) {
                     // don't bother sending to ourself
                     continue;
@@ -157,9 +157,9 @@ utils.inherits(OlmDecryption, base.DecryptionAlgorithm);
  *   problem decrypting the event
  */
 OlmDecryption.prototype.decryptEvent = function(event) {
-    let content = event.getWireContent();
-    let deviceKey = content.sender_key;
-    let ciphertext = content.ciphertext;
+    const content = event.getWireContent();
+    const deviceKey = content.sender_key;
+    const ciphertext = content.ciphertext;
 
     if (!ciphertext) {
         throw new base.DecryptionError("Missing ciphertext");
@@ -168,7 +168,7 @@ OlmDecryption.prototype.decryptEvent = function(event) {
     if (!(this._olmDevice.deviceCurve25519Key in ciphertext)) {
         throw new base.DecryptionError("Not included in recipients");
     }
-    let message = ciphertext[this._olmDevice.deviceCurve25519Key];
+    const message = ciphertext[this._olmDevice.deviceCurve25519Key];
     let payloadString;
 
     try {
@@ -182,7 +182,7 @@ OlmDecryption.prototype.decryptEvent = function(event) {
         throw new base.DecryptionError("Bad Encrypted Message");
     }
 
-    let payload = JSON.parse(payloadString);
+    const payload = JSON.parse(payloadString);
 
     // check that we were the intended recipient, to avoid unknown-key attack
     // https://github.com/vector-im/vector-web/issues/2483
@@ -243,14 +243,14 @@ OlmDecryption.prototype.decryptEvent = function(event) {
  * @return {string} payload, if decrypted successfully.
  */
 OlmDecryption.prototype._decryptMessage = function(theirDeviceIdentityKey, message) {
-    let sessionIds = this._olmDevice.getSessionIdsForDevice(theirDeviceIdentityKey);
+    const sessionIds = this._olmDevice.getSessionIdsForDevice(theirDeviceIdentityKey);
 
     // try each session in turn.
-    let decryptionErrors = {};
+    const decryptionErrors = {};
     for (let i = 0; i < sessionIds.length; i++) {
-        let sessionId = sessionIds[i];
+        const sessionId = sessionIds[i];
         try {
-            let payload = this._olmDevice.decryptMessage(
+            const payload = this._olmDevice.decryptMessage(
                 theirDeviceIdentityKey, sessionId, message.type, message.body
             );
             console.log(
@@ -259,7 +259,7 @@ OlmDecryption.prototype._decryptMessage = function(theirDeviceIdentityKey, messa
             );
             return payload;
         } catch (e) {
-            let foundSession = this._olmDevice.matchesSession(
+            const foundSession = this._olmDevice.matchesSession(
                 theirDeviceIdentityKey, sessionId, message.type, message.body
             );
 
diff --git a/src/crypto/deviceinfo.js b/src/crypto/deviceinfo.js
index d14ff27c0..d3dd682ca 100644
--- a/src/crypto/deviceinfo.js
+++ b/src/crypto/deviceinfo.js
@@ -62,8 +62,8 @@ function DeviceInfo(deviceId) {
  * @return {module:crypto~DeviceInfo} new DeviceInfo
  */
 DeviceInfo.fromStorage = function(obj, deviceId) {
-    let res = new DeviceInfo(deviceId);
-    for (let prop in obj) {
+    const res = new DeviceInfo(deviceId);
+    for (const prop in obj) {
         if (obj.hasOwnProperty(prop)) {
             res[prop] = obj[prop];
         }
@@ -139,7 +139,7 @@ DeviceInfo.DeviceVerification = {
     BLOCKED: -1,
 };
 
-let DeviceVerification = DeviceInfo.DeviceVerification;
+const DeviceVerification = DeviceInfo.DeviceVerification;
 
 /** */
 module.exports = DeviceInfo;
diff --git a/src/crypto/index.js b/src/crypto/index.js
index d22cf8868..ce834d4bf 100644
--- a/src/crypto/index.js
+++ b/src/crypto/index.js
@@ -20,15 +20,15 @@ limitations under the License.
  * @module crypto
  */
 
-let anotherjson = require('another-json');
-let q = require("q");
+const anotherjson = require('another-json');
+const q = require("q");
 
-let utils = require("../utils");
-let OlmDevice = require("./OlmDevice");
-let olmlib = require("./olmlib");
-let algorithms = require("./algorithms");
-let DeviceInfo = require("./deviceinfo");
-let DeviceVerification = DeviceInfo.DeviceVerification;
+const utils = require("../utils");
+const OlmDevice = require("./OlmDevice");
+const olmlib = require("./olmlib");
+const algorithms = require("./algorithms");
+const DeviceInfo = require("./deviceinfo");
+const DeviceVerification = DeviceInfo.DeviceVerification;
 
 /**
  * Cryptography bits
@@ -92,7 +92,7 @@ function Crypto(baseApis, eventEmitter, sessionStore, userId, deviceId) {
 
     if (!myDevices[this._deviceId]) {
         // add our own deviceinfo to the sessionstore
-        let deviceInfo = {
+        const deviceInfo = {
             keys: this._deviceKeys,
             algorithms: this._supportedAlgorithms,
             verified: DeviceVerification.VERIFIED,
@@ -113,7 +113,7 @@ function _registerEventHandlers(crypto, eventEmitter) {
             if (syncState == "PREPARED") {
                 // XXX ugh. we're assuming the eventEmitter is a MatrixClient.
                 // how can we avoid doing so?
-                let rooms = eventEmitter.getRooms();
+                const rooms = eventEmitter.getRooms();
                 crypto._onInitialSyncCompleted(rooms);
             }
         } catch (e) {
@@ -176,7 +176,7 @@ Crypto.prototype.getDeviceEd25519Key = function() {
  * @return {object} A promise that will resolve when the keys are uploaded.
  */
 Crypto.prototype.uploadKeys = function(maxKeys) {
-    let self = this;
+    const self = this;
     return _uploadDeviceKeys(this).then(function(res) {
         // We need to keep a pool of one time public keys on the server so that
         // other devices can start conversations with us. But we can only store
@@ -191,16 +191,16 @@ Crypto.prototype.uploadKeys = function(maxKeys) {
         // these factors.
 
         // We first find how many keys the server has for us.
-        let keyCount = res.one_time_key_counts.signed_curve25519 || 0;
+        const keyCount = res.one_time_key_counts.signed_curve25519 || 0;
         // We then check how many keys we can store in the Account object.
-        let maxOneTimeKeys = self._olmDevice.maxNumberOfOneTimeKeys();
+        const maxOneTimeKeys = self._olmDevice.maxNumberOfOneTimeKeys();
         // Try to keep at most half that number on the server. This leaves the
         // rest of the slots free to hold keys that have been claimed from the
         // server but we haven't recevied a message for.
         // If we run out of slots when generating new keys then olm will
         // discard the oldest private keys first. This will eventually clean
         // out stale private keys that won't receive a message.
-        let keyLimit = Math.floor(maxOneTimeKeys / 2);
+        const keyLimit = Math.floor(maxOneTimeKeys / 2);
         // We work out how many new keys we need to create to top up the server
         // If there are too many keys on the server then we don't need to
         // create any more keys.
@@ -225,10 +225,10 @@ Crypto.prototype.uploadKeys = function(maxKeys) {
 
 // returns a promise which resolves to the response
 function _uploadDeviceKeys(crypto) {
-    let userId = crypto._userId;
-    let deviceId = crypto._deviceId;
+    const userId = crypto._userId;
+    const deviceId = crypto._deviceId;
 
-    let deviceKeys = {
+    const deviceKeys = {
         algorithms: crypto._supportedAlgorithms,
         device_id: deviceId,
         keys: crypto._deviceKeys,
@@ -247,12 +247,12 @@ function _uploadDeviceKeys(crypto) {
 
 // returns a promise which resolves to the response
 function _uploadOneTimeKeys(crypto) {
-    let oneTimeKeys = crypto._olmDevice.getOneTimeKeys();
-    let oneTimeJson = {};
+    const oneTimeKeys = crypto._olmDevice.getOneTimeKeys();
+    const oneTimeJson = {};
 
-    for (let keyId in oneTimeKeys.curve25519) {
+    for (const keyId in oneTimeKeys.curve25519) {
         if (oneTimeKeys.curve25519.hasOwnProperty(keyId)) {
-            let k = {
+            const k = {
                 key: oneTimeKeys.curve25519[keyId],
             };
             crypto._signObject(k);
@@ -282,10 +282,10 @@ function _uploadOneTimeKeys(crypto) {
  * module:crypto/deviceinfo|DeviceInfo}.
  */
 Crypto.prototype.downloadKeys = function(userIds, forceDownload) {
-    let self = this;
+    const self = this;
 
     // promises we need to wait for while the download happens
-    let promises = [];
+    const promises = [];
 
     // list of userids we need to download keys for
     let downloadUsers = [];
@@ -300,9 +300,9 @@ Crypto.prototype.downloadKeys = function(userIds, forceDownload) {
         downloadUsers = userIds;
     } else {
         for (let i = 0; i < userIds.length; ++i) {
-            let u = userIds[i];
+            const u = userIds[i];
 
-            let inprogress = this._keyDownloadsInProgressByUser[u];
+            const inprogress = this._keyDownloadsInProgressByUser[u];
             if (inprogress) {
                 // wait for the download to complete
                 promises.push(q.any(inprogress).catch(perUserCatch(u)));
@@ -313,7 +313,7 @@ Crypto.prototype.downloadKeys = function(userIds, forceDownload) {
     }
 
     if (downloadUsers.length > 0) {
-        let r = this._doKeyDownloadForUsers(downloadUsers);
+        const r = this._doKeyDownloadForUsers(downloadUsers);
         downloadUsers.map(function(u) {
             promises.push(r[u].catch(perUserCatch(u)));
         });
@@ -333,11 +333,11 @@ Crypto.prototype.downloadKeys = function(userIds, forceDownload) {
  * @return {Object} userId->deviceId->{@link module:crypto/deviceinfo|DeviceInfo}.
  */
 Crypto.prototype._getDevicesFromStore = function(userIds) {
-    let stored = {};
-    let self = this;
+    const stored = {};
+    const self = this;
     userIds.map(function(u) {
         stored[u] = {};
-        let devices = self.getStoredDevicesForUser(u) || [];
+        const devices = self.getStoredDevicesForUser(u) || [];
         devices.map(function(dev) {
             stored[u][dev.deviceId] = dev;
         });
@@ -351,17 +351,17 @@ Crypto.prototype._getDevicesFromStore = function(userIds) {
  * @return {Object} a map from userId to a promise for a result for that user
  */
 Crypto.prototype._doKeyDownloadForUsers = function(downloadUsers) {
-    let self = this;
+    const self = this;
 
     console.log('Starting key download for ' + downloadUsers);
 
-    let deferMap = {};
-    let promiseMap = {};
+    const deferMap = {};
+    const promiseMap = {};
 
     downloadUsers.map(function(u) {
-        let deferred = q.defer();
-        let promise = deferred.promise.finally(function() {
-            let inProgress = self._keyDownloadsInProgressByUser[u];
+        const deferred = q.defer();
+        const promise = deferred.promise.finally(function() {
+            const inProgress = self._keyDownloadsInProgressByUser[u];
             utils.removeElement(inProgress, function(e) {
                 return e === promise;
             });
@@ -383,29 +383,29 @@ Crypto.prototype._doKeyDownloadForUsers = function(downloadUsers) {
     this._baseApis.downloadKeysForUsers(
         downloadUsers
     ).done(function(res) {
-        let dk = res.device_keys || {};
+        const dk = res.device_keys || {};
 
         for (let i = 0; i < downloadUsers.length; ++i) {
-            let userId = downloadUsers[i];
+            const userId = downloadUsers[i];
             var deviceId;
 
             console.log('got keys for ' + userId + ':', dk[userId]);
 
             if (!dk[userId]) {
                 // no result for this user
-                let err = 'Unknown';
+                const err = 'Unknown';
                 // TODO: do something with res.failures
                 deferMap[userId].reject(err);
                 continue;
             }
 
             // map from deviceid -> deviceinfo for this user
-            let userStore = {};
-            let devs = self._sessionStore.getEndToEndDevicesForUser(userId);
+            const userStore = {};
+            const devs = self._sessionStore.getEndToEndDevicesForUser(userId);
             if (devs) {
                 for (deviceId in devs) {
                     if (devs.hasOwnProperty(deviceId)) {
-                        let d = DeviceInfo.fromStorage(devs[deviceId], deviceId);
+                        const d = DeviceInfo.fromStorage(devs[deviceId], deviceId);
                         userStore[deviceId] = d;
                     }
                 }
@@ -416,7 +416,7 @@ Crypto.prototype._doKeyDownloadForUsers = function(downloadUsers) {
             );
 
             // update the session store
-            let storage = {};
+            const storage = {};
             for (deviceId in userStore) {
                 if (!userStore.hasOwnProperty(deviceId)) {
                     continue;
@@ -462,7 +462,7 @@ function _updateStoredDeviceKeysForUser(_olmDevice, userId, userStore,
             continue;
         }
 
-        let deviceResult = userResult[deviceId];
+        const deviceResult = userResult[deviceId];
 
         // check that the user_id and device_id in the response object are
         // correct
@@ -496,18 +496,18 @@ function _storeDeviceKeys(_olmDevice, userStore, deviceResult) {
         return false;
     }
 
-    let deviceId = deviceResult.device_id;
-    let userId = deviceResult.user_id;
+    const deviceId = deviceResult.device_id;
+    const userId = deviceResult.user_id;
 
-    let signKeyId = "ed25519:" + deviceId;
-    let signKey = deviceResult.keys[signKeyId];
+    const signKeyId = "ed25519:" + deviceId;
+    const signKey = deviceResult.keys[signKeyId];
     if (!signKey) {
         console.log("Device " + userId + ":" + deviceId +
                     " has no ed25519 key");
         return false;
     }
 
-    let unsigned = deviceResult.unsigned || {};
+    const unsigned = deviceResult.unsigned || {};
 
     try {
         olmlib.verifySignature(_olmDevice, deviceResult, userId, deviceId, signKey);
@@ -552,12 +552,12 @@ function _storeDeviceKeys(_olmDevice, userStore, deviceResult) {
  * managed to get a list of devices for this user yet.
  */
 Crypto.prototype.getStoredDevicesForUser = function(userId) {
-    let devs = this._sessionStore.getEndToEndDevicesForUser(userId);
+    const devs = this._sessionStore.getEndToEndDevicesForUser(userId);
     if (!devs) {
         return null;
     }
-    let res = [];
-    for (let deviceId in devs) {
+    const res = [];
+    for (const deviceId in devs) {
         if (devs.hasOwnProperty(deviceId)) {
             res.push(DeviceInfo.fromStorage(devs[deviceId], deviceId));
         }
@@ -575,7 +575,7 @@ Crypto.prototype.getStoredDevicesForUser = function(userId) {
  * if we don't know about this device
  */
 Crypto.prototype.getStoredDevice = function(userId, deviceId) {
-    let devs = this._sessionStore.getEndToEndDevicesForUser(userId);
+    const devs = this._sessionStore.getEndToEndDevicesForUser(userId);
     if (!devs || !devs[deviceId]) {
         return undefined;
     }
@@ -593,13 +593,13 @@ Crypto.prototype.getStoredDevice = function(userId, deviceId) {
  *    "key", and "display_name" parameters.
  */
 Crypto.prototype.listDeviceKeys = function(userId) {
-    let devices = this.getStoredDevicesForUser(userId) || [];
+    const devices = this.getStoredDevicesForUser(userId) || [];
 
-    let result = [];
+    const result = [];
 
     for (let i = 0; i < devices.length; ++i) {
-        let device = devices[i];
-        let ed25519Key = device.getFingerprint();
+        const device = devices[i];
+        const ed25519Key = device.getFingerprint();
         if (ed25519Key) {
             result.push({
                 id: device.deviceId,
@@ -643,25 +643,25 @@ Crypto.prototype.getDeviceByIdentityKey = function(userId, algorithm, sender_key
         return null;
     }
 
-    let devices = this._sessionStore.getEndToEndDevicesForUser(userId);
+    const devices = this._sessionStore.getEndToEndDevicesForUser(userId);
     if (!devices) {
         return null;
     }
 
-    for (let deviceId in devices) {
+    for (const deviceId in devices) {
         if (!devices.hasOwnProperty(deviceId)) {
             continue;
         }
 
-        let device = devices[deviceId];
-        for (let keyId in device.keys) {
+        const device = devices[deviceId];
+        for (const keyId in device.keys) {
             if (!device.keys.hasOwnProperty(keyId)) {
                 continue;
             }
             if (keyId.indexOf("curve25519:") !== 0) {
                 continue;
             }
-            let deviceKey = device.keys[keyId];
+            const deviceKey = device.keys[keyId];
             if (deviceKey == sender_key) {
                 return DeviceInfo.fromStorage(device, deviceId);
             }
@@ -686,12 +686,12 @@ Crypto.prototype.getDeviceByIdentityKey = function(userId, algorithm, sender_key
  *      leave unchanged.
  */
 Crypto.prototype.setDeviceVerification = function(userId, deviceId, verified, blocked) {
-    let devices = this._sessionStore.getEndToEndDevicesForUser(userId);
+    const devices = this._sessionStore.getEndToEndDevicesForUser(userId);
     if (!devices || !devices[deviceId]) {
         throw new Error("Unknown device " + userId + ":" + deviceId);
     }
 
-    let dev = devices[deviceId];
+    const dev = devices[deviceId];
     let verificationStatus = dev.verified;
 
     if (verified) {
@@ -729,12 +729,12 @@ Crypto.prototype.setDeviceVerification = function(userId, deviceId, verified, bl
  * @return {Object.<string, {deviceIdKey: string, sessions: object[]}>}
  */
 Crypto.prototype.getOlmSessionsForUser = function(userId) {
-    let devices = this.getStoredDevicesForUser(userId) || [];
-    let result = {};
+    const devices = this.getStoredDevicesForUser(userId) || [];
+    const result = {};
     for (let j = 0; j < devices.length; ++j) {
-        let device = devices[j];
-        let deviceKey = device.getIdentityKey();
-        let sessions = this._olmDevice.getSessionInfoForDevice(deviceKey);
+        const device = devices[j];
+        const deviceKey = device.getIdentityKey();
+        const sessions = this._olmDevice.getSessionInfoForDevice(deviceKey);
 
         result[device.deviceId] = {
             deviceIdKey: deviceKey,
@@ -753,8 +753,8 @@ Crypto.prototype.getOlmSessionsForUser = function(userId) {
  * @return {module:crypto/deviceinfo?}
  */
 Crypto.prototype.getEventSenderDeviceInfo = function(event) {
-    let sender_key = event.getSenderKey();
-    let algorithm = event.getWireContent().algorithm;
+    const sender_key = event.getSenderKey();
+    const algorithm = event.getWireContent().algorithm;
 
     if (!sender_key || !algorithm) {
         return null;
@@ -764,7 +764,7 @@ Crypto.prototype.getEventSenderDeviceInfo = function(event) {
     // was sent from. In the case of Megolm, it's actually the Curve25519
     // identity key of the device which set up the Megolm session.
 
-    let device = this.getDeviceByIdentityKey(
+    const device = this.getDeviceByIdentityKey(
         event.getSender(), algorithm, sender_key
     );
 
@@ -781,7 +781,7 @@ Crypto.prototype.getEventSenderDeviceInfo = function(event) {
     //
     // (see https://github.com/vector-im/vector-web/issues/2215)
 
-    let claimedKey = event.getKeysClaimed().ed25519;
+    const claimedKey = event.getKeysClaimed().ed25519;
     if (!claimedKey) {
         console.warn("Event " + event.getId() + " claims no ed25519 key: " +
                      "cannot verify sending device");
@@ -808,7 +808,7 @@ Crypto.prototype.getEventSenderDeviceInfo = function(event) {
 Crypto.prototype.setRoomEncryption = function(roomId, config) {
     // if we already have encryption in this room, we should ignore this event
     // (for now at least. maybe we should alert the user somehow?)
-    let existingConfig = this._sessionStore.getEndToEndRoom(roomId);
+    const existingConfig = this._sessionStore.getEndToEndRoom(roomId);
     if (existingConfig) {
         if (JSON.stringify(existingConfig) != JSON.stringify(config)) {
             console.error("Ignoring m.room.encryption event which requests " +
@@ -817,7 +817,7 @@ Crypto.prototype.setRoomEncryption = function(roomId, config) {
         }
     }
 
-    let AlgClass = algorithms.ENCRYPTION_CLASSES[config.algorithm];
+    const AlgClass = algorithms.ENCRYPTION_CLASSES[config.algorithm];
     if (!AlgClass) {
         throw new Error("Unable to encrypt with " + config.algorithm);
     }
@@ -828,7 +828,7 @@ Crypto.prototype.setRoomEncryption = function(roomId, config) {
     };
     this._sessionStore.storeEndToEndRoom(roomId, config);
 
-    let alg = new AlgClass({
+    const alg = new AlgClass({
         userId: this._userId,
         deviceId: this._deviceId,
         crypto: this,
@@ -859,17 +859,17 @@ Crypto.prototype.setRoomEncryption = function(roomId, config) {
  *    {@link module:crypto~OlmSessionResult}
  */
 Crypto.prototype.ensureOlmSessionsForUsers = function(users) {
-    let devicesByUser = {};
+    const devicesByUser = {};
 
     for (let i = 0; i < users.length; ++i) {
-        let userId = users[i];
+        const userId = users[i];
         devicesByUser[userId] = [];
 
-        let devices = this.getStoredDevicesForUser(userId) || [];
+        const devices = this.getStoredDevicesForUser(userId) || [];
         for (let j = 0; j < devices.length; ++j) {
-            let deviceInfo = devices[j];
+            const deviceInfo = devices[j];
 
-            let key = deviceInfo.getIdentityKey();
+            const key = deviceInfo.getIdentityKey();
             if (key == this._olmDevice.deviceCurve25519Key) {
                 // don't bother setting up session to ourself
                 continue;
@@ -959,9 +959,9 @@ Crypto.prototype.encryptEventIfNeeded = function(event, room) {
         throw new Error("Cannot send encrypted messages in unknown rooms");
     }
 
-    let roomId = event.getRoomId();
+    const roomId = event.getRoomId();
 
-    let alg = this._roomEncryptors[roomId];
+    const alg = this._roomEncryptors[roomId];
     if (!alg) {
         // not encrypting messages in this room
 
@@ -979,7 +979,7 @@ Crypto.prototype.encryptEventIfNeeded = function(event, room) {
     // We can claim and prove ownership of all our device keys in the local
     // echo of the event since we know that all the local echos come from
     // this device.
-    let myKeys = {
+    const myKeys = {
         curve25519: this._olmDevice.deviceCurve25519Key,
         ed25519: this._olmDevice.deviceEd25519Key,
     };
@@ -999,8 +999,8 @@ Crypto.prototype.encryptEventIfNeeded = function(event, room) {
  * @raises {algorithms.DecryptionError} if there is a problem decrypting the event
  */
 Crypto.prototype.decryptEvent = function(event) {
-    let content = event.getWireContent();
-    let alg = this._getRoomDecryptor(event.getRoomId(), content.algorithm);
+    const content = event.getWireContent();
+    const alg = this._getRoomDecryptor(event.getRoomId(), content.algorithm);
     alg.decryptEvent(event);
 };
 
@@ -1011,8 +1011,8 @@ Crypto.prototype.decryptEvent = function(event) {
  * @param {module:models/event.MatrixEvent} event encryption event
  */
 Crypto.prototype._onCryptoEvent = function(event) {
-    let roomId = event.getRoomId();
-    let content = event.getContent();
+    const roomId = event.getRoomId();
+    const content = event.getContent();
 
     try {
         this.setRoomEncryption(roomId, content);
@@ -1043,27 +1043,27 @@ Crypto.prototype._onInitialSyncCompleted = function(rooms) {
     // we need to tell all the devices in all the rooms we are members of that
     // we have arrived.
     // build a list of rooms for each user.
-    let roomsByUser = {};
+    const roomsByUser = {};
     for (let i = 0; i < rooms.length; i++) {
-        let room = rooms[i];
+        const room = rooms[i];
 
         // check for rooms with encryption enabled
-        let alg = this._roomEncryptors[room.roomId];
+        const alg = this._roomEncryptors[room.roomId];
         if (!alg) {
             continue;
         }
 
         // ignore any rooms which we have left
-        let me = room.getMember(this._userId);
+        const me = room.getMember(this._userId);
         if (!me || (
             me.membership !== "join" && me.membership !== "invite"
         )) {
             continue;
         }
 
-        let members = room.getJoinedMembers();
+        const members = room.getJoinedMembers();
         for (let j = 0; j < members.length; j++) {
-            let m = members[j];
+            const m = members[j];
             if (!roomsByUser[m.userId]) {
                 roomsByUser[m.userId] = [];
             }
@@ -1072,8 +1072,8 @@ Crypto.prototype._onInitialSyncCompleted = function(rooms) {
     }
 
     // build a per-device message for each user
-    let content = {};
-    for (let userId in roomsByUser) {
+    const content = {};
+    for (const userId in roomsByUser) {
         if (!roomsByUser.hasOwnProperty(userId)) {
             continue;
         }
@@ -1085,7 +1085,7 @@ Crypto.prototype._onInitialSyncCompleted = function(rooms) {
         };
     }
 
-    let self = this;
+    const self = this;
     this._baseApis.sendToDevice(
         "m.new_device", // OH HAI!
         content
@@ -1101,14 +1101,14 @@ Crypto.prototype._onInitialSyncCompleted = function(rooms) {
  * @param {module:models/event.MatrixEvent} event key event
  */
 Crypto.prototype._onRoomKeyEvent = function(event) {
-    let content = event.getContent();
+    const content = event.getContent();
 
     if (!content.room_id || !content.algorithm) {
         console.error("key event is missing fields");
         return;
     }
 
-    let alg = this._getRoomDecryptor(content.room_id, content.algorithm);
+    const alg = this._getRoomDecryptor(content.room_id, content.algorithm);
     alg.onRoomKeyEvent(event);
 };
 
@@ -1129,9 +1129,9 @@ Crypto.prototype._onRoomMembership = function(event, member, oldMembership) {
     // Further, it is automatically registered and called when new members
     // arrive in the room.
 
-    let roomId = member.roomId;
+    const roomId = member.roomId;
 
-    let alg = this._roomEncryptors[roomId];
+    const alg = this._roomEncryptors[roomId];
     if (!alg) {
         // not encrypting in this room
         return;
@@ -1148,10 +1148,10 @@ Crypto.prototype._onRoomMembership = function(event, member, oldMembership) {
  * @param {module:models/event.MatrixEvent} event announcement event
  */
 Crypto.prototype._onNewDeviceEvent = function(event) {
-    let content = event.getContent();
-    let userId = event.getSender();
-    let deviceId = content.device_id;
-    let rooms = content.rooms;
+    const content = event.getContent();
+    const userId = event.getSender();
+    const deviceId = content.device_id;
+    const rooms = content.rooms;
 
     if (!rooms || !deviceId) {
         console.warn("new_device event missing keys");
@@ -1179,15 +1179,15 @@ Crypto.prototype._onNewDeviceEvent = function(event) {
  * Start device queries for any users who sent us an m.new_device recently
  */
 Crypto.prototype._flushNewDeviceRequests = function() {
-    let self = this;
+    const self = this;
 
-    let users = utils.keys(this._pendingUsersWithNewDevices);
+    const users = utils.keys(this._pendingUsersWithNewDevices);
 
     if (users.length === 0) {
         return;
     }
 
-    let r = this._doKeyDownloadForUsers(users);
+    const r = this._doKeyDownloadForUsers(users);
 
     // we've kicked off requests to these users: remove their
     // pending flag for now.
@@ -1245,7 +1245,7 @@ Crypto.prototype._getRoomDecryptor = function(roomId, algorithm) {
         }
     }
 
-    let AlgClass = algorithms.DECRYPTION_CLASSES[algorithm];
+    const AlgClass = algorithms.DECRYPTION_CLASSES[algorithm];
     if (!AlgClass) {
         throw new algorithms.DecryptionError(
             'Unknown encryption algorithm "' + algorithm + '".'
@@ -1271,7 +1271,7 @@ Crypto.prototype._getRoomDecryptor = function(roomId, algorithm) {
  * @param {Object} obj  Object to which we will add a 'signatures' property
  */
 Crypto.prototype._signObject = function(obj) {
-    let sigs = {};
+    const sigs = {};
     sigs[this._userId] = {};
     sigs[this._userId]["ed25519:" + this._deviceId] =
         this._olmDevice.sign(anotherjson.stringify(obj));
diff --git a/src/crypto/olmlib.js b/src/crypto/olmlib.js
index 0a731e82a..f955c96d8 100644
--- a/src/crypto/olmlib.js
+++ b/src/crypto/olmlib.js
@@ -20,10 +20,10 @@ limitations under the License.
  * Utilities common to olm encryption algorithms
  */
 
-let q = require('q');
-let anotherjson = require('another-json');
+const q = require('q');
+const anotherjson = require('another-json');
 
-let utils = require("../utils");
+const utils = require("../utils");
 
 /**
  * matrix algorithm tag for olm
@@ -54,8 +54,8 @@ module.exports.encryptMessageForDevice = function(
     ourUserId, ourDeviceId, olmDevice, recipientUserId, recipientDevice,
     payloadFields
 ) {
-    let deviceKey = recipientDevice.getIdentityKey();
-    let sessionId = olmDevice.getSessionIdForDevice(deviceKey);
+    const deviceKey = recipientDevice.getIdentityKey();
+    const sessionId = olmDevice.getSessionIdForDevice(deviceKey);
     if (sessionId === null) {
         // If we don't have a session for a device then
         // we can't encrypt a message for it.
@@ -67,7 +67,7 @@ module.exports.encryptMessageForDevice = function(
             recipientUserId + ":" + recipientDevice.deviceId
     );
 
-    let payload = {
+    const payload = {
         sender: ourUserId,
         sender_device: ourDeviceId,
 
@@ -121,22 +121,22 @@ module.exports.encryptMessageForDevice = function(
 module.exports.ensureOlmSessionsForDevices = function(
     olmDevice, baseApis, devicesByUser
 ) {
-    let devicesWithoutSession = [
+    const devicesWithoutSession = [
         // [userId, deviceId], ...
     ];
-    let result = {};
+    const result = {};
 
-    for (let userId in devicesByUser) {
+    for (const userId in devicesByUser) {
         if (!devicesByUser.hasOwnProperty(userId)) {
             continue;
         }
         result[userId] = {};
-        let devices = devicesByUser[userId];
+        const devices = devicesByUser[userId];
         for (let j = 0; j < devices.length; j++) {
-            let deviceInfo = devices[j];
-            let deviceId = deviceInfo.deviceId;
-            let key = deviceInfo.getIdentityKey();
-            let sessionId = olmDevice.getSessionIdForDevice(key);
+            const deviceInfo = devices[j];
+            const deviceId = deviceInfo.deviceId;
+            const key = deviceInfo.getIdentityKey();
+            const sessionId = olmDevice.getSessionIdForDevice(key);
             if (sessionId === null) {
                 devicesWithoutSession.push([userId, deviceId]);
             }
@@ -157,28 +157,28 @@ module.exports.ensureOlmSessionsForDevices = function(
     //
     // That should eventually resolve itself, but it's poor form.
 
-    let oneTimeKeyAlgorithm = "signed_curve25519";
+    const oneTimeKeyAlgorithm = "signed_curve25519";
     return baseApis.claimOneTimeKeys(
         devicesWithoutSession, oneTimeKeyAlgorithm
     ).then(function(res) {
-        let otk_res = res.one_time_keys || {};
-        for (let userId in devicesByUser) {
+        const otk_res = res.one_time_keys || {};
+        for (const userId in devicesByUser) {
             if (!devicesByUser.hasOwnProperty(userId)) {
                 continue;
             }
-            let userRes = otk_res[userId] || {};
-            let devices = devicesByUser[userId];
+            const userRes = otk_res[userId] || {};
+            const devices = devicesByUser[userId];
             for (let j = 0; j < devices.length; j++) {
-                let deviceInfo = devices[j];
-                let deviceId = deviceInfo.deviceId;
+                const deviceInfo = devices[j];
+                const deviceId = deviceInfo.deviceId;
                 if (result[userId][deviceId].sessionId) {
                     // we already have a result for this device
                     continue;
                 }
 
-                let deviceRes = userRes[deviceId] || {};
+                const deviceRes = userRes[deviceId] || {};
                 let oneTimeKey = null;
-                for (let keyId in deviceRes) {
+                for (const keyId in deviceRes) {
                     if (keyId.indexOf(oneTimeKeyAlgorithm + ":") === 0) {
                         oneTimeKey = deviceRes[keyId];
                     }
@@ -192,7 +192,7 @@ module.exports.ensureOlmSessionsForDevices = function(
                     continue;
                 }
 
-                let sid = _verifyKeyAndStartSession(
+                const sid = _verifyKeyAndStartSession(
                     olmDevice, oneTimeKey, userId, deviceInfo
                 );
                 result[userId][deviceId].sessionId = sid;
@@ -204,7 +204,7 @@ module.exports.ensureOlmSessionsForDevices = function(
 
 
 function _verifyKeyAndStartSession(olmDevice, oneTimeKey, userId, deviceInfo) {
-    let deviceId = deviceInfo.deviceId;
+    const deviceId = deviceInfo.deviceId;
     try {
         _verifySignature(
             olmDevice, oneTimeKey, userId, deviceId,
@@ -250,13 +250,13 @@ function _verifyKeyAndStartSession(olmDevice, oneTimeKey, userId, deviceInfo) {
  *
  * @param {string} signingKey   base64-ed ed25519 public key
  */
-let _verifySignature = module.exports.verifySignature = function(
+const _verifySignature = module.exports.verifySignature = function(
     olmDevice, obj, signingUserId, signingDeviceId, signingKey
 ) {
-    let signKeyId = "ed25519:" + signingDeviceId;
-    let signatures = obj.signatures || {};
-    let userSigs = signatures[signingUserId] || {};
-    let signature = userSigs[signKeyId];
+    const signKeyId = "ed25519:" + signingDeviceId;
+    const signatures = obj.signatures || {};
+    const userSigs = signatures[signingUserId] || {};
+    const signature = userSigs[signKeyId];
     if (!signature) {
         throw Error("No signature");
     }
@@ -265,7 +265,7 @@ let _verifySignature = module.exports.verifySignature = function(
     // anotherjson
     delete obj.unsigned;
     delete obj.signatures;
-    let json = anotherjson.stringify(obj);
+    const json = anotherjson.stringify(obj);
 
     olmDevice.verifySignature(
         signingKey, json, signature
diff --git a/src/filter-component.js b/src/filter-component.js
index b0c56479b..f1861f6f2 100644
--- a/src/filter-component.js
+++ b/src/filter-component.js
@@ -27,7 +27,7 @@ limitations under the License.
  */
 function _matches_wildcard(actual_value, filter_value) {
     if (filter_value.endsWith("*")) {
-        let type_prefix = filter_value.slice(0, -1);
+        const type_prefix = filter_value.slice(0, -1);
         return actual_value.substr(0, type_prefix.length) === type_prefix;
     } else {
         return actual_value === filter_value;
@@ -84,7 +84,7 @@ FilterComponent.prototype.check = function(event) {
  */
 FilterComponent.prototype._checkFields =
     function(room_id, sender, event_type, contains_url) {
-    let literal_keys = {
+    const literal_keys = {
         "rooms": function(v) {
             return room_id === v;
         },
@@ -96,16 +96,16 @@ FilterComponent.prototype._checkFields =
         },
     };
 
-    let self = this;
+    const self = this;
     Object.keys(literal_keys).forEach(function(name) {
-        let match_func = literal_keys[name];
-        let not_name = "not_" + name;
-        let disallowed_values = self[not_name];
+        const match_func = literal_keys[name];
+        const not_name = "not_" + name;
+        const disallowed_values = self[not_name];
         if (disallowed_values.map(match_func)) {
             return false;
         }
 
-        let allowed_values = self[name];
+        const allowed_values = self[name];
         if (allowed_values) {
             if (!allowed_values.map(match_func)) {
                 return false;
@@ -113,7 +113,7 @@ FilterComponent.prototype._checkFields =
         }
     });
 
-    let contains_url_filter = this.filter_json.contains_url;
+    const contains_url_filter = this.filter_json.contains_url;
     if (contains_url_filter !== undefined) {
         if (contains_url_filter !== contains_url) {
             return false;
diff --git a/src/filter.js b/src/filter.js
index c64b7aff1..c8fa08b71 100644
--- a/src/filter.js
+++ b/src/filter.js
@@ -18,7 +18,7 @@ limitations under the License.
  * @module filter
  */
 
-let FilterComponent = require("./filter-component");
+const FilterComponent = require("./filter-component");
 
 /**
  * @param {Object} obj
@@ -26,7 +26,7 @@ let FilterComponent = require("./filter-component");
  * @param {*} val
  */
 function setProp(obj, keyNesting, val) {
-    let nestedKeys = keyNesting.split(".");
+    const nestedKeys = keyNesting.split(".");
     let currentObj = obj;
     for (let i = 0; i < (nestedKeys.length - 1); i++) {
         if (!currentObj[nestedKeys[i]]) {
@@ -106,10 +106,10 @@ Filter.prototype.setDefinition = function(definition) {
     //   "event_fields": ["type", "content", "sender"]
     // }
 
-    let room_filter_json = definition.room;
+    const room_filter_json = definition.room;
 
     // consider the top level rooms/not_rooms filter
-    let room_filter_fields = {};
+    const room_filter_fields = {};
     if (room_filter_json) {
         if (room_filter_json.rooms) {
             room_filter_fields.rooms = room_filter_json.rooms;
@@ -183,7 +183,7 @@ Filter.prototype.setIncludeLeaveRooms = function(includeLeave) {
  * @return {Filter}
  */
 Filter.fromJson = function(userId, filterId, jsonObj) {
-    let filter = new Filter(userId, filterId);
+    const filter = new Filter(userId, filterId);
     filter.setDefinition(jsonObj);
     return filter;
 };
diff --git a/src/http-api.js b/src/http-api.js
index c26458690..c9ce7a121 100644
--- a/src/http-api.js
+++ b/src/http-api.js
@@ -18,13 +18,13 @@ limitations under the License.
  * This is an internal module. See {@link MatrixHttpApi} for the public class.
  * @module http-api
  */
-let q = require("q");
-let utils = require("./utils");
+const q = require("q");
+const utils = require("./utils");
 
 // we use our own implementation of setTimeout, so that if we get suspended in
 // the middle of a /sync, we cancel the sync as soon as we awake, rather than
 // waiting for the delay to elapse.
-let callbacks = require("./realtime-callbacks");
+const callbacks = require("./realtime-callbacks");
 
 /*
 TODO:
@@ -91,7 +91,7 @@ module.exports.MatrixHttpApi.prototype = {
      *          path and query parameters respectively.
      */
     getContentUri: function() {
-        let params = {
+        const params = {
             access_token: this.opts.accessToken,
         };
         return {
@@ -145,12 +145,12 @@ module.exports.MatrixHttpApi.prototype = {
 
         // if the file doesn't have a mime type, use a default since
         // the HS errors if we don't supply one.
-        let contentType = opts.type || file.type || 'application/octet-stream';
-        let fileName = opts.name || file.name;
+        const contentType = opts.type || file.type || 'application/octet-stream';
+        const fileName = opts.name || file.name;
 
         // we used to recommend setting file.stream to the thing to upload on
         // nodejs.
-        let body = file.stream ? file.stream : file;
+        const body = file.stream ? file.stream : file;
 
         // backwards-compatibility hacks where we used to do different things
         // between browser and node.
@@ -192,7 +192,7 @@ module.exports.MatrixHttpApi.prototype = {
         // (browser-request doesn't support progress either, which is also kind
         // of important here)
 
-        let upload = { loaded: 0, total: 0 };
+        const upload = { loaded: 0, total: 0 };
         let promise;
 
         // XMLHttpRequest doesn't parse JSON for us. request normally does, but
@@ -214,12 +214,12 @@ module.exports.MatrixHttpApi.prototype = {
         }
 
         if (global.XMLHttpRequest) {
-            let defer = q.defer();
-            let xhr = new global.XMLHttpRequest();
+            const defer = q.defer();
+            const xhr = new global.XMLHttpRequest();
             upload.xhr = xhr;
-            let cb = requestCallback(defer, opts.callback, this.opts.onlyData);
+            const cb = requestCallback(defer, opts.callback, this.opts.onlyData);
 
-            let timeout_fn = function() {
+            const timeout_fn = function() {
                 xhr.abort();
                 cb(new Error('Timeout'));
             };
@@ -269,7 +269,7 @@ module.exports.MatrixHttpApi.prototype = {
             // dirty hack (as per _request) to allow the upload to be cancelled.
             promise.abort = xhr.abort.bind(xhr);
         } else {
-            let queryParams = {
+            const queryParams = {
                 filename: fileName,
             };
 
@@ -283,10 +283,10 @@ module.exports.MatrixHttpApi.prototype = {
             );
         }
 
-        let self = this;
+        const self = this;
 
         // remove the upload from the list on completion
-        let promise0 = promise.finally(function() {
+        const promise0 = promise.finally(function() {
             for (let i = 0; i < self.uploads.length; ++i) {
                 if (self.uploads[i] === upload) {
                     self.uploads.splice(i, 1);
@@ -317,7 +317,7 @@ module.exports.MatrixHttpApi.prototype = {
     },
 
     idServerRequest: function(callback, method, path, params, prefix) {
-        let fullUri = this.opts.idBaseUrl + prefix + path;
+        const fullUri = this.opts.idBaseUrl + prefix + path;
 
         if (callback !== undefined && !utils.isFunction(callback)) {
             throw Error(
@@ -325,7 +325,7 @@ module.exports.MatrixHttpApi.prototype = {
             );
         }
 
-        let opts = {
+        const opts = {
             uri: fullUri,
             method: method,
             withCredentials: false,
@@ -338,7 +338,7 @@ module.exports.MatrixHttpApi.prototype = {
             opts.form = params;
         }
 
-        let defer = q.defer();
+        const defer = q.defer();
         this.opts.request(
             opts,
             requestCallback(defer, callback, this.opts.onlyData)
@@ -389,11 +389,11 @@ module.exports.MatrixHttpApi.prototype = {
             queryParams.access_token = this.opts.accessToken;
         }
 
-        let request_promise = this.request(
+        const request_promise = this.request(
             callback, method, path, queryParams, data, opts
         );
 
-        let self = this;
+        const self = this;
         request_promise.catch(function(err) {
             if (err.errcode == 'M_UNKNOWN_TOKEN') {
                 self.event_emitter.emit("Session.logged_out");
@@ -437,8 +437,8 @@ module.exports.MatrixHttpApi.prototype = {
      */
     request: function(callback, method, path, queryParams, data, opts) {
         opts = opts || {};
-        let prefix = opts.prefix !== undefined ? opts.prefix : this.opts.prefix;
-        let fullUri = this.opts.baseUrl + prefix + path;
+        const prefix = opts.prefix !== undefined ? opts.prefix : this.opts.prefix;
+        const fullUri = this.opts.baseUrl + prefix + path;
 
         return this.requestOtherUrl(
             callback, method, fullUri, queryParams, data, opts
@@ -613,9 +613,9 @@ module.exports.MatrixHttpApi.prototype = {
         }
         opts = opts || {};
 
-        let self = this;
+        const self = this;
         if (this.opts.extraParams) {
-            for (let key in this.opts.extraParams) {
+            for (const key in this.opts.extraParams) {
                 if (!this.opts.extraParams.hasOwnProperty(key)) {
                     continue;
                 }
@@ -623,14 +623,14 @@ module.exports.MatrixHttpApi.prototype = {
             }
         }
 
-        let json = opts.json === undefined ? true : opts.json;
+        const json = opts.json === undefined ? true : opts.json;
 
-        let defer = q.defer();
+        const defer = q.defer();
 
         let timeoutId;
         let timedOut = false;
         let req;
-        let localTimeoutMs = opts.localTimeoutMs || this.opts.localTimeoutMs;
+        const localTimeoutMs = opts.localTimeoutMs || this.opts.localTimeoutMs;
         if (localTimeoutMs) {
             timeoutId = callbacks.setTimeout(function() {
                 timedOut = true;
@@ -645,7 +645,7 @@ module.exports.MatrixHttpApi.prototype = {
             }, localTimeoutMs);
         }
 
-        let reqPromise = defer.promise;
+        const reqPromise = defer.promise;
 
         try {
             req = this.opts.request(
@@ -670,8 +670,8 @@ module.exports.MatrixHttpApi.prototype = {
 
                     // if json is falsy, we won't parse any error response, so need
                     // to do so before turning it into a MatrixError
-                    let parseErrorJson = !json;
-                    let handlerFn = requestCallback(
+                    const parseErrorJson = !json;
+                    const handlerFn = requestCallback(
                         defer, callback, self.opts.onlyData,
                         parseErrorJson,
                         opts.bodyParser
@@ -705,7 +705,7 @@ module.exports.MatrixHttpApi.prototype = {
  * If parseErrorJson is true, we will JSON.parse the body if we get a 4xx error.
  *
  */
-let requestCallback = function(
+const requestCallback = function(
     defer, userDefinedCallback, onlyData,
     parseErrorJson, bodyParser
 ) {
@@ -735,7 +735,7 @@ let requestCallback = function(
             defer.reject(err);
             userDefinedCallback(err);
         } else {
-            let res = {
+            const res = {
                 code: response.statusCode,
                 headers: response.headers,
                 data: body,
diff --git a/src/interactive-auth.js b/src/interactive-auth.js
index d4e2d7f14..bd557c2fb 100644
--- a/src/interactive-auth.js
+++ b/src/interactive-auth.js
@@ -16,9 +16,9 @@ limitations under the License.
 "use strict";
 
 /** @module interactive-auth */
-let q = require("q");
+const q = require("q");
 
-let utils = require("./utils");
+const utils = require("./utils");
 
 /**
  * Abstracts the logic used to drive the interactive auth process.
@@ -115,7 +115,7 @@ InteractiveAuth.prototype = {
         }
 
         // use the sessionid from the last request.
-        let auth = {
+        const auth = {
             session: this._data.session,
         };
         utils.extend(auth, authData);
@@ -131,7 +131,7 @@ InteractiveAuth.prototype = {
      * @param {object?} auth new auth dict, including session id
      */
     _doRequest: function(auth) {
-        let self = this;
+        const self = this;
 
         // hackery to make sure that synchronous exceptions end up in the catch
         // handler (without the additional event loop entailed by q.fcall or an
@@ -164,7 +164,7 @@ InteractiveAuth.prototype = {
      * @private
      */
     _startNextAuthStage: function() {
-        let nextStage = this._chooseStage();
+        const nextStage = this._chooseStage();
         if (!nextStage) {
             throw new Error("No incomplete flows from the server");
         }
@@ -186,9 +186,9 @@ InteractiveAuth.prototype = {
      * @return {string?} login type
      */
     _chooseStage: function() {
-        let flow = this._chooseFlow();
+        const flow = this._chooseFlow();
         console.log("Active flow => %s", JSON.stringify(flow));
-        let nextStage = this._firstUncompletedStage(flow);
+        const nextStage = this._firstUncompletedStage(flow);
         console.log("Next stage: %s", nextStage);
         return nextStage;
     },
@@ -200,7 +200,7 @@ InteractiveAuth.prototype = {
      * @return {object} flow
      */
     _chooseFlow: function() {
-        let flows = this._data.flows || [];
+        const flows = this._data.flows || [];
         // always use the first flow for now
         return flows[0];
     },
@@ -213,9 +213,9 @@ InteractiveAuth.prototype = {
      * @return {string} login type
      */
     _firstUncompletedStage: function(flow) {
-        let completed = (this._data || {}).completed || [];
+        const completed = (this._data || {}).completed || [];
         for (let i = 0; i < flow.stages.length; ++i) {
-            let stageType = flow.stages[i];
+            const stageType = flow.stages[i];
             if (completed.indexOf(stageType) === -1) {
                 return stageType;
             }
diff --git a/src/matrix.js b/src/matrix.js
index b434d6551..26aef56fe 100644
--- a/src/matrix.js
+++ b/src/matrix.js
@@ -94,7 +94,7 @@ module.exports.getRequest = function() {
  * @param {requestWrapperFunction} wrapper The wrapping function.
  */
 module.exports.wrapRequest = function(wrapper) {
-    let origRequest = request;
+    const origRequest = request;
     request = function(options, callback) {
         return wrapper(origRequest, options, callback);
     };
diff --git a/src/models/event-timeline-set.js b/src/models/event-timeline-set.js
index 911a4046d..9bc2b9df4 100644
--- a/src/models/event-timeline-set.js
+++ b/src/models/event-timeline-set.js
@@ -17,12 +17,12 @@ limitations under the License.
 /**
  * @module models/event-timeline-set
  */
-let EventEmitter = require("events").EventEmitter;
-let utils = require("../utils");
-let EventTimeline = require("./event-timeline");
+const EventEmitter = require("events").EventEmitter;
+const utils = require("../utils");
+const EventTimeline = require("./event-timeline");
 
 // var DEBUG = false;
-let DEBUG = true;
+const DEBUG = true;
 
 let debuglog;
 if (DEBUG) {
@@ -136,7 +136,7 @@ EventTimelineSet.prototype.eventIdToTimeline = function(eventId) {
  * @param {String} newEventId  event ID of the replacement event
  */
 EventTimelineSet.prototype.replaceEventId = function(oldEventId, newEventId) {
-    let existingTimeline = this._eventIdToTimeline[oldEventId];
+    const existingTimeline = this._eventIdToTimeline[oldEventId];
     if (existingTimeline) {
         delete this._eventIdToTimeline[oldEventId];
         this._eventIdToTimeline[newEventId] = existingTimeline;
@@ -166,13 +166,13 @@ EventTimelineSet.prototype.resetLiveTimeline = function(backPaginationToken, flu
     }
 
     // initialise the state in the new timeline from our last known state
-    let evMap = this._liveTimeline.getState(EventTimeline.FORWARDS).events;
-    let events = [];
-    for (let evtype in evMap) {
+    const evMap = this._liveTimeline.getState(EventTimeline.FORWARDS).events;
+    const events = [];
+    for (const evtype in evMap) {
         if (!evMap.hasOwnProperty(evtype)) {
             continue;
         }
-        for (let stateKey in evMap[evtype]) {
+        for (const stateKey in evMap[evtype]) {
             if (!evMap[evtype].hasOwnProperty(stateKey)) {
                 continue;
             }
@@ -198,7 +198,7 @@ EventTimelineSet.prototype.resetLiveTimeline = function(backPaginationToken, flu
  * the given event, or null if unknown
  */
 EventTimelineSet.prototype.getTimelineForEvent = function(eventId) {
-    let res = this._eventIdToTimeline[eventId];
+    const res = this._eventIdToTimeline[eventId];
     return (res === undefined) ? null : res;
 };
 
@@ -209,7 +209,7 @@ EventTimelineSet.prototype.getTimelineForEvent = function(eventId) {
  * @return {?module:models/event~MatrixEvent} the given event, or undefined if unknown
  */
 EventTimelineSet.prototype.findEventById = function(eventId) {
-    let tl = this.getTimelineForEvent(eventId);
+    const tl = this.getTimelineForEvent(eventId);
     if (!tl) {
         return undefined;
     }
@@ -230,7 +230,7 @@ EventTimelineSet.prototype.addTimeline = function() {
                         " it.");
     }
 
-    let timeline = new EventTimeline(this);
+    const timeline = new EventTimeline(this);
     this._timelines.push(timeline);
     return timeline;
 };
@@ -277,9 +277,9 @@ EventTimelineSet.prototype.addEventsToTimeline = function(events, toStartOfTimel
         }
     }
 
-    let direction = toStartOfTimeline ? EventTimeline.BACKWARDS :
+    const direction = toStartOfTimeline ? EventTimeline.BACKWARDS :
         EventTimeline.FORWARDS;
-    let inverseDirection = toStartOfTimeline ? EventTimeline.FORWARDS :
+    const inverseDirection = toStartOfTimeline ? EventTimeline.FORWARDS :
         EventTimeline.BACKWARDS;
 
     // Adding events to timelines can be quite complicated. The following
@@ -354,10 +354,10 @@ EventTimelineSet.prototype.addEventsToTimeline = function(events, toStartOfTimel
     let didUpdate = false;
     let lastEventWasNew = false;
     for (let i = 0; i < events.length; i++) {
-        let event = events[i];
-        let eventId = event.getId();
+        const event = events[i];
+        const eventId = event.getId();
 
-        let existingTimeline = this._eventIdToTimeline[eventId];
+        const existingTimeline = this._eventIdToTimeline[eventId];
 
         if (!existingTimeline) {
             // we don't know about this event yet. Just add it to the timeline.
@@ -374,7 +374,7 @@ EventTimelineSet.prototype.addEventsToTimeline = function(events, toStartOfTimel
             continue;
         }
 
-        let neighbour = timeline.getNeighbouringTimeline(direction);
+        const neighbour = timeline.getNeighbouringTimeline(direction);
         if (neighbour) {
             // this timeline already has a neighbour in the relevant direction;
             // let's assume the timelines are already correctly linked up, and
@@ -422,18 +422,18 @@ EventTimelineSet.prototype.addEventsToTimeline = function(events, toStartOfTimel
  */
 EventTimelineSet.prototype.addLiveEvent = function(event, duplicateStrategy) {
     if (this._filter) {
-        let events = this._filter.filterRoomTimeline([event]);
+        const events = this._filter.filterRoomTimeline([event]);
         if (!events.length) {
             return;
         }
     }
 
-    let timeline = this._eventIdToTimeline[event.getId()];
+    const timeline = this._eventIdToTimeline[event.getId()];
     if (timeline) {
         if (duplicateStrategy === "replace") {
             debuglog("EventTimelineSet.addLiveEvent: replacing duplicate event " +
                      event.getId());
-            let tlEvents = timeline.getEvents();
+            const tlEvents = timeline.getEvents();
             for (let j = 0; j < tlEvents.length; j++) {
                 if (tlEvents[j].getId() === event.getId()) {
                     // still need to set the right metadata on this event
@@ -475,11 +475,11 @@ EventTimelineSet.prototype.addLiveEvent = function(event, duplicateStrategy) {
  */
 EventTimelineSet.prototype.addEventToTimeline = function(event, timeline,
                                                          toStartOfTimeline) {
-    let eventId = event.getId();
+    const eventId = event.getId();
     timeline.addEvent(event, toStartOfTimeline);
     this._eventIdToTimeline[eventId] = timeline;
 
-    let data = {
+    const data = {
         timeline: timeline,
         liveEvent: !toStartOfTimeline && timeline == this._liveTimeline,
     };
@@ -500,7 +500,7 @@ EventTimelineSet.prototype.addEventToTimeline = function(event, timeline,
 EventTimelineSet.prototype.handleRemoteEcho = function(localEvent, oldEventId,
                                                         newEventId) {
     // XXX: why don't we infer newEventId from localEvent?
-    let existingTimeline = this._eventIdToTimeline[oldEventId];
+    const existingTimeline = this._eventIdToTimeline[oldEventId];
     if (existingTimeline) {
         delete this._eventIdToTimeline[oldEventId];
         this._eventIdToTimeline[newEventId] = existingTimeline;
@@ -524,15 +524,15 @@ EventTimelineSet.prototype.handleRemoteEcho = function(localEvent, oldEventId,
  * in this room.
  */
 EventTimelineSet.prototype.removeEvent = function(eventId) {
-    let timeline = this._eventIdToTimeline[eventId];
+    const timeline = this._eventIdToTimeline[eventId];
     if (!timeline) {
         return null;
     }
 
-    let removed = timeline.removeEvent(eventId);
+    const removed = timeline.removeEvent(eventId);
     if (removed) {
         delete this._eventIdToTimeline[eventId];
-        let data = {
+        const data = {
             timeline: timeline,
         };
         this.emit("Room.timeline", removed, this.room, undefined, true, data);
@@ -558,8 +558,8 @@ EventTimelineSet.prototype.compareEventOrdering = function(eventId1, eventId2) {
         return 0;
     }
 
-    let timeline1 = this._eventIdToTimeline[eventId1];
-    let timeline2 = this._eventIdToTimeline[eventId2];
+    const timeline1 = this._eventIdToTimeline[eventId1];
+    const timeline2 = this._eventIdToTimeline[eventId2];
 
     if (timeline1 === undefined) {
         return null;
@@ -572,10 +572,10 @@ EventTimelineSet.prototype.compareEventOrdering = function(eventId1, eventId2) {
         // both events are in the same timeline - figure out their
         // relative indices
         let idx1, idx2;
-        let events = timeline1.getEvents();
+        const events = timeline1.getEvents();
         for (let idx = 0; idx < events.length &&
              (idx1 === undefined || idx2 === undefined); idx++) {
-            let evId = events[idx].getId();
+            const evId = events[idx].getId();
             if (evId == eventId1) {
                 idx1 = idx;
             }
diff --git a/src/models/event-timeline.js b/src/models/event-timeline.js
index e9b574bef..7bdee758c 100644
--- a/src/models/event-timeline.js
+++ b/src/models/event-timeline.js
@@ -4,9 +4,9 @@
  * @module models/event-timeline
  */
 
-let RoomState = require("./room-state");
-let utils = require("../utils");
-let MatrixEvent = require("./event").MatrixEvent;
+const RoomState = require("./room-state");
+const utils = require("../utils");
+const MatrixEvent = require("./event").MatrixEvent;
 
 /**
  * Construct a new EventTimeline
@@ -75,7 +75,7 @@ EventTimeline.prototype.initialiseState = function(stateEvents) {
 
     // we deep-copy the events here, in case they get changed later - we don't
     // want changes to the start state leaking through to the end state.
-    let oldStateEvents = utils.map(
+    const oldStateEvents = utils.map(
         utils.deepCopy(
             stateEvents.map(function(mxEvent) {
                 return mxEvent.event;
@@ -237,10 +237,10 @@ EventTimeline.prototype.setNeighbouringTimeline = function(neighbour, direction)
  * @param {boolean}  atStart     true to insert new event at the start
  */
 EventTimeline.prototype.addEvent = function(event, atStart) {
-    let stateContext = atStart ? this._startState : this._endState;
+    const stateContext = atStart ? this._startState : this._endState;
 
     // only call setEventMetadata on the unfiltered timelineSets
-    let timelineSet = this.getTimelineSet();
+    const timelineSet = this.getTimelineSet();
     if (timelineSet.room &&
         timelineSet.room.getUnfilteredTimelineSet() === timelineSet) {
         EventTimeline.setEventMetadata(event, stateContext, atStart);
@@ -314,7 +314,7 @@ EventTimeline.setEventMetadata = function(event, stateContext, toStartOfTimeline
  */
 EventTimeline.prototype.removeEvent = function(eventId) {
     for (let i = this._events.length - 1; i >= 0; i--) {
-        let ev = this._events[i];
+        const ev = this._events[i];
         if (ev.getId() == eventId) {
             this._events.splice(i, 1);
             if (i < this._baseIndex) {
diff --git a/src/models/event.js b/src/models/event.js
index 38686239c..40442b75d 100644
--- a/src/models/event.js
+++ b/src/models/event.js
@@ -21,9 +21,9 @@ limitations under the License.
  * @module models/event
  */
 
-let EventEmitter = require("events").EventEmitter;
+const EventEmitter = require("events").EventEmitter;
 
-let utils = require('../utils.js');
+const utils = require('../utils.js');
 
 /**
  * Enum for event statuses.
@@ -350,8 +350,8 @@ utils.extend(module.exports.MatrixEvent.prototype, {
             }
         }
 
-        let keeps = _REDACT_KEEP_CONTENT_MAP[this.getType()] || {};
-        let content = this.getContent();
+        const keeps = _REDACT_KEEP_CONTENT_MAP[this.getType()] || {};
+        const content = this.getContent();
         for (key in content) {
             if (!content.hasOwnProperty(key)) {
                 continue;
@@ -424,7 +424,7 @@ utils.extend(module.exports.MatrixEvent.prototype, {
  *    m.room.aliases allows key aliases
  */
 // a map giving the keys we keep when an event is redacted
-let _REDACT_KEEP_KEY_MAP = [
+const _REDACT_KEEP_KEY_MAP = [
     'event_id', 'type', 'room_id', 'user_id', 'state_key', 'prev_state',
     'content', 'unsigned',
 ].reduce(function(ret, val) {
@@ -432,7 +432,7 @@ let _REDACT_KEEP_KEY_MAP = [
 }, {});
 
 // a map from event type to the .content keys we keep when an event is redacted
-let _REDACT_KEEP_CONTENT_MAP = {
+const _REDACT_KEEP_CONTENT_MAP = {
     'm.room.member': {'membership': 1},
     'm.room.create': {'creator': 1},
     'm.room.join_rules': {'join_rule': 1},
diff --git a/src/models/room-member.js b/src/models/room-member.js
index f749e92e0..c88b4c28b 100644
--- a/src/models/room-member.js
+++ b/src/models/room-member.js
@@ -17,10 +17,10 @@ limitations under the License.
 /**
  * @module models/room-member
  */
-let EventEmitter = require("events").EventEmitter;
-let ContentRepo = require("../content-repo");
+const EventEmitter = require("events").EventEmitter;
+const ContentRepo = require("../content-repo");
 
-let utils = require("../utils");
+const utils = require("../utils");
 
 /**
  * Construct a new room member.
@@ -73,10 +73,10 @@ RoomMember.prototype.setMembershipEvent = function(event, roomState) {
     }
     this.events.member = event;
 
-    let oldMembership = this.membership;
+    const oldMembership = this.membership;
     this.membership = event.getDirectionalContent().membership;
 
-    let oldName = this.name;
+    const oldName = this.name;
     this.name = calculateDisplayName(this, event, roomState);
     if (oldMembership !== this.membership) {
         this._updateModifiedTime();
@@ -103,8 +103,8 @@ RoomMember.prototype.setPowerLevelEvent = function(powerLevelEvent) {
     utils.forEach(utils.values(powerLevelEvent.getContent().users), function(lvl) {
         maxLevel = Math.max(maxLevel, lvl);
     });
-    let oldPowerLevel = this.powerLevel;
-    let oldPowerLevelNorm = this.powerLevelNorm;
+    const oldPowerLevel = this.powerLevel;
+    const oldPowerLevelNorm = this.powerLevelNorm;
 
     if (powerLevelEvent.getContent().users[this.userId] !== undefined) {
         this.powerLevel = powerLevelEvent.getContent().users[this.userId];
@@ -136,9 +136,9 @@ RoomMember.prototype.setTypingEvent = function(event) {
     if (event.getType() !== "m.typing") {
         return;
     }
-    let oldTyping = this.typing;
+    const oldTyping = this.typing;
     this.typing = false;
-    let typingList = event.getContent().user_ids;
+    const typingList = event.getContent().user_ids;
     if (!utils.isArray(typingList)) {
         // malformed event :/ bail early. TODO: whine?
         return;
@@ -195,8 +195,8 @@ RoomMember.prototype.getAvatarUrl =
     if (!this.events.member && !allowDefault) {
         return null;
     }
-    let rawUrl = this.events.member ? this.events.member.getContent().avatar_url : null;
-    let httpUrl = ContentRepo.getHttpUriForMxc(
+    const rawUrl = this.events.member ? this.events.member.getContent().avatar_url : null;
+    const httpUrl = ContentRepo.getHttpUriForMxc(
         baseUrl, rawUrl, width, height, resizeMethod, allowDirectLinks
     );
     if (httpUrl) {
@@ -210,8 +210,8 @@ RoomMember.prototype.getAvatarUrl =
 };
 
 function calculateDisplayName(member, event, roomState) {
-    let displayName = event.getDirectionalContent().displayname;
-    let selfUserId = member.userId;
+    const displayName = event.getDirectionalContent().displayname;
+    const selfUserId = member.userId;
 
     if (!displayName) {
         return selfUserId;
@@ -221,8 +221,8 @@ function calculateDisplayName(member, event, roomState) {
         return displayName;
     }
 
-    let userIds = roomState.getUserIdsWithDisplayName(displayName);
-    let otherUsers = userIds.filter(function(u) {
+    const userIds = roomState.getUserIdsWithDisplayName(displayName);
+    const otherUsers = userIds.filter(function(u) {
         return u !== selfUserId;
     });
     if (otherUsers.length > 0) {
diff --git a/src/models/room-state.js b/src/models/room-state.js
index 6becc8bc3..a90414d5c 100644
--- a/src/models/room-state.js
+++ b/src/models/room-state.js
@@ -17,10 +17,10 @@ limitations under the License.
 /**
  * @module models/room-state
  */
-let EventEmitter = require("events").EventEmitter;
+const EventEmitter = require("events").EventEmitter;
 
-let utils = require("../utils");
-let RoomMember = require("./room-member");
+const utils = require("../utils");
+const RoomMember = require("./room-member");
 
 /**
  * Construct room state.
@@ -100,7 +100,7 @@ RoomState.prototype.getStateEvents = function(eventType, stateKey) {
     if (stateKey === undefined) { // return all values
         return utils.values(this.events[eventType]);
     }
-    let event = this.events[eventType][stateKey];
+    const event = this.events[eventType][stateKey];
     return event ? event : null;
 };
 
@@ -115,7 +115,7 @@ RoomState.prototype.getStateEvents = function(eventType, stateKey) {
  * @fires module:client~MatrixClient#event:"RoomState.events"
  */
 RoomState.prototype.setStateEvents = function(stateEvents) {
-    let self = this;
+    const self = this;
     this._updateModifiedTime();
 
     // update the core event dict
@@ -153,7 +153,7 @@ RoomState.prototype.setStateEvents = function(stateEvents) {
         }
 
         if (event.getType() === "m.room.member") {
-            let userId = event.getStateKey();
+            const userId = event.getStateKey();
 
             // leave events apparently elide the displayname or avatar_url,
             // so let's fake one up so that we don't leak user ids
@@ -178,11 +178,11 @@ RoomState.prototype.setStateEvents = function(stateEvents) {
             // so we don't make assumptions about the properties of RoomMember
             // (e.g. and manage to break it because deep copying doesn't do
             // everything).
-            let sentinel = new RoomMember(event.getRoomId(), userId);
+            const sentinel = new RoomMember(event.getRoomId(), userId);
             utils.forEach([member, sentinel], function(roomMember) {
                 roomMember.setMembershipEvent(event, self);
                 // this member may have a power level already, so set it.
-                let pwrLvlEvent = self.getStateEvents("m.room.power_levels", "");
+                const pwrLvlEvent = self.getStateEvents("m.room.power_levels", "");
                 if (pwrLvlEvent) {
                     roomMember.setPowerLevelEvent(pwrLvlEvent);
                 }
@@ -192,7 +192,7 @@ RoomState.prototype.setStateEvents = function(stateEvents) {
             self.members[userId] = member;
             self.emit("RoomState.members", event, self, member);
         } else if (event.getType() === "m.room.power_levels") {
-            let members = utils.values(self.members);
+            const members = utils.values(self.members);
             utils.forEach(members, function(member) {
                 member.setPowerLevelEvent(event);
                 self.emit("RoomState.members", event, self, member);
@@ -312,12 +312,12 @@ RoomState.prototype.maySendStateEvent = function(stateEventType, userId) {
  *                        according to the room's state.
  */
 RoomState.prototype._maySendEventOfType = function(eventType, userId, state) {
-    let member = this.getMember(userId);
+    const member = this.getMember(userId);
     if (!member || member.membership == 'leave') {
         return false;
     }
 
-    let power_levels_event = this.getStateEvents('m.room.power_levels', '');
+    const power_levels_event = this.getStateEvents('m.room.power_levels', '');
 
     let power_levels;
     let events_levels = {};
@@ -355,11 +355,11 @@ function _updateThirdPartyTokenCache(roomState, memberEvent) {
     if (!memberEvent.getContent().third_party_invite) {
         return;
     }
-    let token = (memberEvent.getContent().third_party_invite.signed || {}).token;
+    const token = (memberEvent.getContent().third_party_invite.signed || {}).token;
     if (!token) {
         return;
     }
-    let threePidInvite = roomState.getStateEvents(
+    const threePidInvite = roomState.getStateEvents(
         "m.room.third_party_invite", token
     );
     if (!threePidInvite) {
@@ -369,14 +369,14 @@ function _updateThirdPartyTokenCache(roomState, memberEvent) {
 }
 
 function _updateDisplayNameCache(roomState, userId, displayName) {
-    let oldName = roomState._userIdsToDisplayNames[userId];
+    const oldName = roomState._userIdsToDisplayNames[userId];
     delete roomState._userIdsToDisplayNames[userId];
     if (oldName) {
         // Remove the old name from the cache.
         // We clobber the user_id > name lookup but the name -> [user_id] lookup
         // means we need to remove that user ID from that array rather than nuking
         // the lot.
-        let existingUserIds = roomState._displayNameToUserIds[oldName] || [];
+        const existingUserIds = roomState._displayNameToUserIds[oldName] || [];
         for (let i = 0; i < existingUserIds.length; i++) {
             if (existingUserIds[i] === userId) {
                 // remove this user ID from this array
diff --git a/src/models/room.js b/src/models/room.js
index bf4baddac..a7faddba5 100644
--- a/src/models/room.js
+++ b/src/models/room.js
@@ -17,22 +17,22 @@ limitations under the License.
 /**
  * @module models/room
  */
-let EventEmitter = require("events").EventEmitter;
+const EventEmitter = require("events").EventEmitter;
 
-let EventStatus = require("./event").EventStatus;
-let RoomSummary = require("./room-summary");
-let MatrixEvent = require("./event").MatrixEvent;
-let utils = require("../utils");
-let ContentRepo = require("../content-repo");
-let EventTimeline = require("./event-timeline");
-let EventTimelineSet = require("./event-timeline-set");
+const EventStatus = require("./event").EventStatus;
+const RoomSummary = require("./room-summary");
+const MatrixEvent = require("./event").MatrixEvent;
+const utils = require("../utils");
+const ContentRepo = require("../content-repo");
+const EventTimeline = require("./event-timeline");
+const EventTimelineSet = require("./event-timeline-set");
 
 
 function synthesizeReceipt(userId, event, receiptType) {
     // console.log("synthesizing receipt for "+event.getId());
     // This is really ugly because JS has no way to express an object literal
     // where the name of a key comes from an expression
-    let fakeReceipt = {
+    const fakeReceipt = {
         content: {},
         type: "m.receipt",
         room_id: event.getRoomId(),
@@ -308,7 +308,7 @@ Room.prototype.setUnreadNotificationCount = function(type, count) {
  */
 Room.prototype.getAvatarUrl = function(baseUrl, width, height, resizeMethod,
                                        allowDefault) {
-    let roomAvatarEvent = this.currentState.getStateEvents("m.room.avatar", "");
+    const roomAvatarEvent = this.currentState.getStateEvents("m.room.avatar", "");
     if (allowDefault === undefined) {
         allowDefault = true;
     }
@@ -316,7 +316,7 @@ Room.prototype.getAvatarUrl = function(baseUrl, width, height, resizeMethod,
         return null;
     }
 
-    let mainUrl = roomAvatarEvent ? roomAvatarEvent.getContent().url : null;
+    const mainUrl = roomAvatarEvent ? roomAvatarEvent.getContent().url : null;
     if (mainUrl) {
         return ContentRepo.getHttpUriForMxc(
             baseUrl, mainUrl, width, height, resizeMethod
@@ -337,12 +337,12 @@ Room.prototype.getAvatarUrl = function(baseUrl, width, height, resizeMethod,
  * @return {array} The room's alias as an array of strings
  */
 Room.prototype.getAliases = function() {
-    let alias_strings = [];
+    const alias_strings = [];
 
-    let alias_events = this.currentState.getStateEvents("m.room.aliases");
+    const alias_events = this.currentState.getStateEvents("m.room.aliases");
     if (alias_events) {
         for (let i = 0; i < alias_events.length; ++i) {
-            let alias_event = alias_events[i];
+            const alias_event = alias_events[i];
             if (utils.isArray(alias_event.getContent().aliases)) {
                 Array.prototype.push.apply(
                     alias_strings, alias_event.getContent().aliases
@@ -360,7 +360,7 @@ Room.prototype.getAliases = function() {
  * @return {?string} The room's canonical alias, or null if there is none
  */
 Room.prototype.getCanonicalAlias = function() {
-    let canonicalAlias = this.currentState.getStateEvents("m.room.canonical_alias", "");
+    const canonicalAlias = this.currentState.getStateEvents("m.room.canonical_alias", "");
     if (canonicalAlias) {
         return canonicalAlias.getContent().alias;
     }
@@ -400,7 +400,7 @@ Room.prototype.addEventsToTimeline = function(events, toStartOfTimeline,
  * @return {RoomMember} The member or <code>null</code>.
  */
  Room.prototype.getMember = function(userId) {
-    let member = this.currentState.members[userId];
+    const member = this.currentState.members[userId];
     if (!member) {
         return null;
     }
@@ -445,7 +445,7 @@ Room.prototype.addEventsToTimeline = function(events, toStartOfTimeline,
  * @return {boolean} True if this user_id has the given membership state.
  */
  Room.prototype.hasMembershipState = function(userId, membership) {
-    let member = this.getMember(userId);
+    const member = this.getMember(userId);
     if (!member) {
         return false;
     }
@@ -461,8 +461,8 @@ Room.prototype.getOrCreateFilteredTimelineSet = function(filter) {
     if (this._filteredTimelineSets[filter.filterId]) {
         return this._filteredTimelineSets[filter.filterId];
     }
-    let opts = Object.assign({ filter: filter }, this._opts);
-    let timelineSet = new EventTimelineSet(this, opts);
+    const opts = Object.assign({ filter: filter }, this._opts);
+    const timelineSet = new EventTimelineSet(this, opts);
     reEmit(this, timelineSet, ["Room.timeline", "Room.timelineReset"]);
     this._filteredTimelineSets[filter.filterId] = timelineSet;
     this._timelineSets.push(timelineSet);
@@ -474,7 +474,7 @@ Room.prototype.getOrCreateFilteredTimelineSet = function(filter) {
     // may have grown huge and so take a long time to filter.
     // see https://github.com/vector-im/vector-web/issues/2109
 
-    let unfilteredLiveTimeline = this.getLiveTimeline();
+    const unfilteredLiveTimeline = this.getLiveTimeline();
 
     unfilteredLiveTimeline.getEvents().forEach(function(event) {
         timelineSet.addLiveEvent(event);
@@ -508,9 +508,9 @@ Room.prototype.getOrCreateFilteredTimelineSet = function(filter) {
  * @param {Filter} filter  the filter whose timelineSet is to be forgotten
  */
 Room.prototype.removeFilteredTimelineSet = function(filter) {
-    let timelineSet = this._filteredTimelineSets[filter.filterId];
+    const timelineSet = this._filteredTimelineSets[filter.filterId];
     delete this._filteredTimelineSets[filter.filterId];
-    let i = this._timelineSets.indexOf(timelineSet);
+    const i = this._timelineSets.indexOf(timelineSet);
     if (i > -1) {
         this._timelineSets.splice(i, 1);
     }
@@ -528,10 +528,10 @@ Room.prototype.removeFilteredTimelineSet = function(filter) {
 Room.prototype._addLiveEvent = function(event, duplicateStrategy) {
     let i;
     if (event.getType() === "m.room.redaction") {
-        let redactId = event.event.redacts;
+        const redactId = event.event.redacts;
 
         // if we know about this event, redact its contents now.
-        let redactedEvent = this.getUnfilteredTimelineSet().findEventById(redactId);
+        const redactedEvent = this.getUnfilteredTimelineSet().findEventById(redactId);
         if (redactedEvent) {
             redactedEvent.makeRedacted(event);
             this.emit("Room.redaction", event, this);
@@ -551,7 +551,7 @@ Room.prototype._addLiveEvent = function(event, duplicateStrategy) {
     }
 
     if (event.getUnsigned().transaction_id) {
-        let existingEvent = this._txnToEvent[event.getUnsigned().transaction_id];
+        const existingEvent = this._txnToEvent[event.getUnsigned().transaction_id];
         if (existingEvent) {
             // remote echo of an event we sent earlier
             this._handleRemoteEcho(event, existingEvent);
@@ -625,7 +625,7 @@ Room.prototype.addPendingEvent = function(event, txnId) {
         this._pendingEventList.push(event);
     } else {
         for (let i = 0; i < this._timelineSets.length; i++) {
-            let timelineSet = this._timelineSets[i];
+            const timelineSet = this._timelineSets[i];
             if (timelineSet.getFilter()) {
                 if (this._filter.filterRoomTimeline([event]).length) {
                     timelineSet.addEventToTimeline(event,
@@ -656,9 +656,9 @@ Room.prototype.addPendingEvent = function(event, txnId) {
  * @private
  */
 Room.prototype._handleRemoteEcho = function(remoteEvent, localEvent) {
-    let oldEventId = localEvent.getId();
-    let newEventId = remoteEvent.getId();
-    let oldStatus = localEvent.status;
+    const oldEventId = localEvent.getId();
+    const newEventId = remoteEvent.getId();
+    const oldStatus = localEvent.status;
 
     // no longer pending
     delete this._txnToEvent[remoteEvent.transaction_id];
@@ -678,7 +678,7 @@ Room.prototype._handleRemoteEcho = function(remoteEvent, localEvent) {
     localEvent.handleRemoteEcho(remoteEvent.event);
 
     for (let i = 0; i < this._timelineSets.length; i++) {
-        let timelineSet = this._timelineSets[i];
+        const timelineSet = this._timelineSets[i];
 
         // if it's already in the timeline, update the timeline map. If it's not, add it.
         timelineSet.handleRemoteEcho(localEvent, oldEventId, newEventId);
@@ -690,7 +690,7 @@ Room.prototype._handleRemoteEcho = function(remoteEvent, localEvent) {
 
 /* a map from current event status to a list of allowed next statuses
  */
-let ALLOWED_TRANSITIONS = {};
+const ALLOWED_TRANSITIONS = {};
 
 ALLOWED_TRANSITIONS[EventStatus.ENCRYPTING] = [
     EventStatus.SENDING,
@@ -737,7 +737,7 @@ Room.prototype.updatePendingEvent = function(event, newStatus, newEventId) {
 
     // SENT races against /sync, so we have to special-case it.
     if (newStatus == EventStatus.SENT) {
-        let timeline = this.getUnfilteredTimelineSet().eventIdToTimeline(newEventId);
+        const timeline = this.getUnfilteredTimelineSet().eventIdToTimeline(newEventId);
         if (timeline) {
             // we've already received the event via the event stream.
             // nothing more to do here.
@@ -745,15 +745,15 @@ Room.prototype.updatePendingEvent = function(event, newStatus, newEventId) {
         }
     }
 
-    let oldStatus = event.status;
-    let oldEventId = event.getId();
+    const oldStatus = event.status;
+    const oldEventId = event.getId();
 
     if (!oldStatus) {
         throw new Error("updatePendingEventStatus called on an event which is " +
                         "not a local echo.");
     }
 
-    let allowed = ALLOWED_TRANSITIONS[oldStatus];
+    const allowed = ALLOWED_TRANSITIONS[oldStatus];
     if (!allowed || allowed.indexOf(newStatus) < 0) {
         throw new Error("Invalid EventStatus transition " + oldStatus + "->" +
                         newStatus);
@@ -812,7 +812,7 @@ Room.prototype.addLiveEvents = function(events, duplicateStrategy) {
 
     // sanity check that the live timeline is still live
     for (i = 0; i < this._timelineSets.length; i++) {
-        let liveTimeline = this._timelineSets[i].getLiveTimeline();
+        const liveTimeline = this._timelineSets[i].getLiveTimeline();
         if (liveTimeline.getPaginationToken(EventTimeline.FORWARDS)) {
             throw new Error(
                 "live timeline " + i + " is no longer live - it has a pagination token " +
@@ -863,7 +863,7 @@ Room.prototype.removeEvents = function(event_ids) {
 Room.prototype.removeEvent = function(eventId) {
     let removedAny = false;
     for (let i = 0; i < this._timelineSets.length; i++) {
-        let removed = this._timelineSets[i].removeEvent(eventId);
+        const removed = this._timelineSets[i].removeEvent(eventId);
         if (removed) {
             removedAny = true;
         }
@@ -882,14 +882,14 @@ Room.prototype.removeEvent = function(eventId) {
 Room.prototype.recalculate = function(userId) {
     // set fake stripped state events if this is an invite room so logic remains
     // consistent elsewhere.
-    let self = this;
-    let membershipEvent = this.currentState.getStateEvents(
+    const self = this;
+    const membershipEvent = this.currentState.getStateEvents(
         "m.room.member", userId
     );
     if (membershipEvent && membershipEvent.getContent().membership === "invite") {
-        let strippedStateEvents = membershipEvent.event.invite_room_state || [];
+        const strippedStateEvents = membershipEvent.event.invite_room_state || [];
         utils.forEach(strippedStateEvents, function(strippedEvent) {
-            let existingEvent = self.currentState.getStateEvents(
+            const existingEvent = self.currentState.getStateEvents(
                 strippedEvent.type, strippedEvent.state_key
             );
             if (!existingEvent) {
@@ -906,7 +906,7 @@ Room.prototype.recalculate = function(userId) {
         });
     }
 
-    let oldName = this.name;
+    const oldName = this.name;
     this.name = calculateRoomName(this, userId);
     this.summary = new RoomSummary(this.roomId, {
         title: this.name,
@@ -1004,18 +1004,18 @@ Room.prototype.addReceipt = function(event, fake) {
  * @param {Object} receipts The object to add receipts to
  */
 Room.prototype._addReceiptsToStructure = function(event, receipts) {
-    let self = this;
+    const self = this;
     utils.keys(event.getContent()).forEach(function(eventId) {
         utils.keys(event.getContent()[eventId]).forEach(function(receiptType) {
             utils.keys(event.getContent()[eventId][receiptType]).forEach(
             function(userId) {
-                let receipt = event.getContent()[eventId][receiptType][userId];
+                const receipt = event.getContent()[eventId][receiptType][userId];
 
                 if (!receipts[receiptType]) {
                     receipts[receiptType] = {};
                 }
 
-                let existingReceipt = receipts[receiptType][userId];
+                const existingReceipt = receipts[receiptType][userId];
 
                 if (!existingReceipt) {
                     receipts[receiptType][userId] = {};
@@ -1024,7 +1024,7 @@ Room.prototype._addReceiptsToStructure = function(event, receipts) {
                     // than the one we already have. (This is managed
                     // server-side, but because we synthesize RRs locally we
                     // have to do it here too.)
-                    let ordering = self.getUnfilteredTimelineSet().compareEventOrdering(
+                    const ordering = self.getUnfilteredTimelineSet().compareEventOrdering(
                         existingReceipt.eventId, eventId);
                     if (ordering !== null && ordering >= 0) {
                         return;
@@ -1046,10 +1046,10 @@ Room.prototype._addReceiptsToStructure = function(event, receipts) {
  * @return {Object} Map of receipts by event ID
  */
 Room.prototype._buildReceiptCache = function(receipts) {
-    let receiptCacheByEventId = {};
+    const receiptCacheByEventId = {};
     utils.keys(receipts).forEach(function(receiptType) {
         utils.keys(receipts[receiptType]).forEach(function(userId) {
-            let receipt = receipts[receiptType][userId];
+            const receipt = receipts[receiptType][userId];
             if (!receiptCacheByEventId[receipt.eventId]) {
                 receiptCacheByEventId[receipt.eventId] = [];
             }
@@ -1102,7 +1102,7 @@ Room.prototype.addTags = function(event) {
  */
 Room.prototype.addAccountData = function(events) {
     for (let i = 0; i < events.length; i++) {
-        let event = events[i];
+        const event = events[i];
         if (event.getType() === "m.tag") {
             this.addTags(event);
         }
@@ -1134,7 +1134,7 @@ function calculateRoomName(room, userId, ignoreRoomNameEvent) {
     if (!ignoreRoomNameEvent) {
         // check for an alias, if any. for now, assume first alias is the
         // official one.
-        let mRoomName = room.currentState.getStateEvents("m.room.name", "");
+        const mRoomName = room.currentState.getStateEvents("m.room.name", "");
         if (mRoomName && mRoomName.getContent() && mRoomName.getContent().name) {
             return mRoomName.getContent().name;
         }
@@ -1143,7 +1143,7 @@ function calculateRoomName(room, userId, ignoreRoomNameEvent) {
     let alias = room.getCanonicalAlias();
 
     if (!alias) {
-        let aliases = room.getAliases();
+        const aliases = room.getAliases();
 
         if (aliases.length) {
             alias = aliases[0];
@@ -1154,16 +1154,16 @@ function calculateRoomName(room, userId, ignoreRoomNameEvent) {
     }
 
     // get members that are NOT ourselves and are actually in the room.
-    let otherMembers = utils.filter(room.currentState.getMembers(), function(m) {
+    const otherMembers = utils.filter(room.currentState.getMembers(), function(m) {
         return (m.userId !== userId && m.membership !== "leave");
     });
-    let allMembers = utils.filter(room.currentState.getMembers(), function(m) {
+    const allMembers = utils.filter(room.currentState.getMembers(), function(m) {
         return (m.membership !== "leave");
     });
-    let myMemberEventArray = utils.filter(room.currentState.getMembers(), function(m) {
+    const myMemberEventArray = utils.filter(room.currentState.getMembers(), function(m) {
         return (m.userId == userId);
     });
-    let myMemberEvent = (
+    const myMemberEvent = (
         (myMemberEventArray.length && myMemberEventArray[0].events) ?
             myMemberEventArray[0].events.member.event : undefined
     );
@@ -1190,7 +1190,7 @@ function calculateRoomName(room, userId, ignoreRoomNameEvent) {
             // self-chat, peeked room with 1 participant,
             // or inbound invite, or outbound 3PID invite.
             if (allMembers[0].userId === userId) {
-                let thirdPartyInvites =
+                const thirdPartyInvites =
                     room.currentState.getStateEvents("m.room.third_party_invite");
                 if (thirdPartyInvites && thirdPartyInvites.length > 0) {
                     let name = "Inviting " +
@@ -1238,7 +1238,7 @@ function reEmit(reEmitEntity, emittableEntity, eventNames) {
             // Transformation Example:
             // listener on "foo" => function(a,b) { ... }
             // Re-emit on "thing" => thing.emit("foo", a, b)
-            let newArgs = [eventName];
+            const newArgs = [eventName];
             for (let i = 0; i < arguments.length; i++) {
                 newArgs.push(arguments[i]);
             }
diff --git a/src/models/search-result.js b/src/models/search-result.js
index 3c36cc8d9..bab76fa83 100644
--- a/src/models/search-result.js
+++ b/src/models/search-result.js
@@ -19,8 +19,8 @@ limitations under the License.
  * @module models/search-result
  */
 
-let EventContext = require("./event-context");
-let utils = require("../utils");
+const EventContext = require("./event-context");
+const utils = require("../utils");
 
 /**
  * Construct a new SearchResult
@@ -45,11 +45,11 @@ function SearchResult(rank, eventContext) {
  */
 
 SearchResult.fromJson = function(jsonObj, eventMapper) {
-    let jsonContext = jsonObj.context || {};
-    let events_before = jsonContext.events_before || [];
-    let events_after = jsonContext.events_after || [];
+    const jsonContext = jsonObj.context || {};
+    const events_before = jsonContext.events_before || [];
+    const events_after = jsonContext.events_after || [];
 
-    let context = new EventContext(eventMapper(jsonObj.result));
+    const context = new EventContext(eventMapper(jsonObj.result));
 
     context.setPaginateToken(jsonContext.start, true);
     context.addEvents(utils.map(events_before, eventMapper), true);
diff --git a/src/models/user.js b/src/models/user.js
index f89404503..dbfaeb791 100644
--- a/src/models/user.js
+++ b/src/models/user.js
@@ -17,8 +17,8 @@ limitations under the License.
 /**
  * @module models/user
  */
- let EventEmitter = require("events").EventEmitter;
- let utils = require("../utils");
+ const EventEmitter = require("events").EventEmitter;
+ const utils = require("../utils");
 
 /**
  * Construct a new User. A User must have an ID and can optionally have extra
@@ -73,10 +73,10 @@ User.prototype.setPresenceEvent = function(event) {
     if (event.getType() !== "m.presence") {
         return;
     }
-    let firstFire = this.events.presence === null;
+    const firstFire = this.events.presence === null;
     this.events.presence = event;
 
-    let eventsToFire = [];
+    const eventsToFire = [];
     if (event.getContent().presence !== this.presence || firstFire) {
         eventsToFire.push("User.presence");
     }
@@ -122,7 +122,7 @@ User.prototype.setPresenceEvent = function(event) {
  * @param {string} name The new display name.
  */
 User.prototype.setDisplayName = function(name) {
-    let oldName = this.displayName;
+    const oldName = this.displayName;
     this.displayName = name;
     if (name !== oldName) {
         this._updateModifiedTime();
@@ -146,7 +146,7 @@ User.prototype.setRawDisplayName = function(name) {
  * @param {string} url The new avatar URL.
  */
 User.prototype.setAvatarUrl = function(url) {
-    let oldUrl = this.avatarUrl;
+    const oldUrl = this.avatarUrl;
     this.avatarUrl = url;
     if (url !== oldUrl) {
         this._updateModifiedTime();
diff --git a/src/pushprocessor.js b/src/pushprocessor.js
index f8cb110c4..5b35ccdf4 100644
--- a/src/pushprocessor.js
+++ b/src/pushprocessor.js
@@ -23,25 +23,25 @@ limitations under the License.
  * @param {Object} client The Matrix client object to use
  */
 function PushProcessor(client) {
-    let escapeRegExp = function(string) {
+    const escapeRegExp = function(string) {
         return string.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
     };
 
-    let matchingRuleFromKindSet = function(ev, kindset, device) {
-        let rulekinds_in_order = ['override', 'content', 'room', 'sender', 'underride'];
+    const matchingRuleFromKindSet = function(ev, kindset, device) {
+        const rulekinds_in_order = ['override', 'content', 'room', 'sender', 'underride'];
         for (let ruleKindIndex = 0;
                 ruleKindIndex < rulekinds_in_order.length;
                 ++ruleKindIndex) {
-            let kind = rulekinds_in_order[ruleKindIndex];
-            let ruleset = kindset[kind];
+            const kind = rulekinds_in_order[ruleKindIndex];
+            const ruleset = kindset[kind];
 
             for (let ruleIndex = 0; ruleIndex < ruleset.length; ++ruleIndex) {
-                let rule = ruleset[ruleIndex];
+                const rule = ruleset[ruleIndex];
                 if (!rule.enabled) {
                     continue;
                 }
 
-                let rawrule = templateRuleToRaw(kind, rule, device);
+                const rawrule = templateRuleToRaw(kind, rule, device);
                 if (!rawrule) {
                     continue;
                 }
@@ -55,8 +55,8 @@ function PushProcessor(client) {
         return null;
     };
 
-    let templateRuleToRaw = function(kind, tprule, device) {
-        let rawrule = {
+    const templateRuleToRaw = function(kind, tprule, device) {
+        const rawrule = {
             'rule_id': tprule.rule_id,
             'actions': tprule.actions,
             'conditions': [],
@@ -106,18 +106,18 @@ function PushProcessor(client) {
         return rawrule;
     };
 
-    let ruleMatchesEvent = function(rule, ev) {
+    const ruleMatchesEvent = function(rule, ev) {
         let ret = true;
         for (let i = 0; i < rule.conditions.length; ++i) {
-            let cond = rule.conditions[i];
+            const cond = rule.conditions[i];
             ret &= eventFulfillsCondition(cond, ev);
         }
         //console.log("Rule "+rule.rule_id+(ret ? " matches" : " doesn't match"));
         return ret;
     };
 
-    let eventFulfillsCondition = function(cond, ev) {
-        let condition_functions = {
+    const eventFulfillsCondition = function(cond, ev) {
+        const condition_functions = {
             "event_match": eventFulfillsEventMatchCondition,
             "device": eventFulfillsDeviceCondition,
             "contains_display_name": eventFulfillsDisplayNameCondition,
@@ -129,26 +129,26 @@ function PushProcessor(client) {
         return true;
     };
 
-    let eventFulfillsRoomMemberCountCondition = function(cond, ev) {
+    const eventFulfillsRoomMemberCountCondition = function(cond, ev) {
         if (!cond.is) {
             return false;
         }
 
-        let room = client.getRoom(ev.getRoomId());
+        const room = client.getRoom(ev.getRoomId());
         if (!room || !room.currentState || !room.currentState.members) {
             return false;
         }
 
-        let memberCount = Object.keys(room.currentState.members).filter(function(m) {
+        const memberCount = Object.keys(room.currentState.members).filter(function(m) {
             return room.currentState.members[m].membership == 'join';
         }).length;
 
-        let m = cond.is.match(/^([=<>]*)([0-9]*)$/);
+        const m = cond.is.match(/^([=<>]*)([0-9]*)$/);
         if (!m) {
             return false;
         }
-        let ineq = m[1];
-        let rhs = parseInt(m[2]);
+        const ineq = m[1];
+        const rhs = parseInt(m[2]);
         if (isNaN(rhs)) {
             return false;
         }
@@ -169,32 +169,32 @@ function PushProcessor(client) {
         }
     };
 
-    let eventFulfillsDisplayNameCondition = function(cond, ev) {
-        let content = ev.getContent();
+    const eventFulfillsDisplayNameCondition = function(cond, ev) {
+        const content = ev.getContent();
         if (!content || !content.body || typeof content.body != 'string') {
             return false;
         }
 
-        let room = client.getRoom(ev.getRoomId());
+        const room = client.getRoom(ev.getRoomId());
         if (!room || !room.currentState || !room.currentState.members ||
             !room.currentState.getMember(client.credentials.userId)) {
             return false;
         }
 
-        let displayName = room.currentState.getMember(client.credentials.userId).name;
+        const displayName = room.currentState.getMember(client.credentials.userId).name;
 
         // N.B. we can't use \b as it chokes on unicode. however \W seems to be okay
         // as shorthand for [^0-9A-Za-z_].
-        let pat = new RegExp("(^|\\W)" + escapeRegExp(displayName) + "(\\W|$)", 'i');
+        const pat = new RegExp("(^|\\W)" + escapeRegExp(displayName) + "(\\W|$)", 'i');
         return content.body.search(pat) > -1;
     };
 
-    let eventFulfillsDeviceCondition = function(cond, ev) {
+    const eventFulfillsDeviceCondition = function(cond, ev) {
         return false; // XXX: Allow a profile tag to be set for the web client instance
     };
 
-    let eventFulfillsEventMatchCondition = function(cond, ev) {
-        let val = valueForDottedKey(cond.key, ev);
+    const eventFulfillsEventMatchCondition = function(cond, ev) {
+        const val = valueForDottedKey(cond.key, ev);
         if (!val || typeof val != 'string') {
             return false;
         }
@@ -205,11 +205,11 @@ function PushProcessor(client) {
         } else {
             pat = '^' + globToRegexp(cond.pattern) + '$';
         }
-        let regex = new RegExp(pat, 'i');
+        const regex = new RegExp(pat, 'i');
         return !!val.match(regex);
     };
 
-    let globToRegexp = function(glob) {
+    const globToRegexp = function(glob) {
         // From
         // https://github.com/matrix-org/synapse/blob/abbee6b29be80a77e05730707602f3bbfc3f38cb/synapse/push/__init__.py#L132
         // Because micromatch is about 130KB with dependencies,
@@ -218,19 +218,19 @@ function PushProcessor(client) {
         pat = pat.replace(/\\\*/, '.*');
         pat = pat.replace(/\?/, '.');
         pat = pat.replace(/\\\[(!|)(.*)\\]/, function(match, p1, p2, offset, string) {
-            let first = p1 && '^' || '';
-            let second = p2.replace(/\\\-/, '-');
+            const first = p1 && '^' || '';
+            const second = p2.replace(/\\\-/, '-');
             return '[' + first + second + ']';
         });
         return pat;
     };
 
-    let valueForDottedKey = function(key, ev) {
-        let parts = key.split('.');
+    const valueForDottedKey = function(key, ev) {
+        const parts = key.split('.');
         let val;
 
         // special-case the first component to deal with encrypted messages
-        let firstPart = parts[0];
+        const firstPart = parts[0];
         if (firstPart == 'content') {
             val = ev.getContent();
             parts.shift();
@@ -243,7 +243,7 @@ function PushProcessor(client) {
         }
 
         while (parts.length > 0) {
-            let thispart = parts.shift();
+            const thispart = parts.shift();
             if (!val[thispart]) {
                 return null;
             }
@@ -252,7 +252,7 @@ function PushProcessor(client) {
         return val;
     };
 
-    let matchingRuleForEventWithRulesets = function(ev, rulesets) {
+    const matchingRuleForEventWithRulesets = function(ev, rulesets) {
         if (!rulesets || !rulesets.device) {
             return null;
         }
@@ -260,12 +260,12 @@ function PushProcessor(client) {
             return null;
         }
 
-        let allDevNames = Object.keys(rulesets.device);
+        const allDevNames = Object.keys(rulesets.device);
         for (let i = 0; i < allDevNames.length; ++i) {
-            let devname = allDevNames[i];
-            let devrules = rulesets.device[devname];
+            const devname = allDevNames[i];
+            const devrules = rulesets.device[devname];
 
-            let matchingRule = matchingRuleFromKindSet(devrules, devname);
+            const matchingRule = matchingRuleFromKindSet(devrules, devname);
             if (matchingRule) {
                 return matchingRule;
             }
@@ -273,13 +273,13 @@ function PushProcessor(client) {
         return matchingRuleFromKindSet(ev, rulesets.global);
     };
 
-    let pushActionsForEventAndRulesets = function(ev, rulesets) {
-        let rule = matchingRuleForEventWithRulesets(ev, rulesets);
+    const pushActionsForEventAndRulesets = function(ev, rulesets) {
+        const rule = matchingRuleForEventWithRulesets(ev, rulesets);
         if (!rule) {
             return {};
         }
 
-        let actionObj = PushProcessor.actionListToActionsObject(rule.actions);
+        const actionObj = PushProcessor.actionListToActionsObject(rule.actions);
 
         // Some actions are implicit in some situations: we add those here
         if (actionObj.tweaks.highlight === undefined) {
@@ -312,9 +312,9 @@ function PushProcessor(client) {
  * @return {object} A object with key 'notify' (true or false) and an object of actions
  */
 PushProcessor.actionListToActionsObject = function(actionlist) {
-    let actionobj = { 'notify': false, 'tweaks': {} };
+    const actionobj = { 'notify': false, 'tweaks': {} };
     for (let i = 0; i < actionlist.length; ++i) {
-        let action = actionlist[i];
+        const action = actionlist[i];
         if (action === 'notify') {
             actionobj.notify = true;
         } else if (typeof action === 'object') {
diff --git a/src/realtime-callbacks.js b/src/realtime-callbacks.js
index 63f75e155..f682119de 100644
--- a/src/realtime-callbacks.js
+++ b/src/realtime-callbacks.js
@@ -27,7 +27,7 @@ limitations under the License.
 
 // we schedule a callback at least this often, to check if we've missed out on
 // some wall-clock time due to being suspended.
-let TIMER_CHECK_PERIOD_MS = 1000;
+const TIMER_CHECK_PERIOD_MS = 1000;
 
 // counter, for making up ids to return from setTimeout
 let _count = 0;
@@ -37,10 +37,10 @@ let _realCallbackKey;
 
 // a sorted list of the callbacks to be run.
 // each is an object with keys [runAt, func, params, key].
-let _callbackList = [];
+const _callbackList = [];
 
 // var debuglog = console.log.bind(console);
-let debuglog = function() {};
+const debuglog = function() {};
 
 /**
  * Replace the function used by this module to get the current time.
@@ -72,12 +72,12 @@ module.exports.setTimeout = function(func, delayMs) {
         delayMs = 0;
     }
 
-    let params = Array.prototype.slice.call(arguments, 2);
-    let runAt = _now() + delayMs;
-    let key = _count++;
+    const params = Array.prototype.slice.call(arguments, 2);
+    const runAt = _now() + delayMs;
+    const key = _count++;
     debuglog("setTimeout: scheduling cb", key, "at", runAt,
              "(delay", delayMs, ")");
-    let data = {
+    const data = {
         runAt: runAt,
         func: func,
         params: params,
@@ -85,7 +85,7 @@ module.exports.setTimeout = function(func, delayMs) {
     };
 
     // figure out where it goes in the list
-    let idx = binarySearch(
+    const idx = binarySearch(
         _callbackList, function(el) {
             return el.runAt - runAt;
         }
@@ -110,7 +110,7 @@ module.exports.clearTimeout = function(key) {
     // remove the element from the list
     let i;
     for (i = 0; i < _callbackList.length; i++) {
-        let cb = _callbackList[i];
+        const cb = _callbackList[i];
         if (cb.key == key) {
             _callbackList.splice(i, 1);
             break;
@@ -129,15 +129,15 @@ function _scheduleRealCallback() {
         global.clearTimeout(_realCallbackKey);
     }
 
-    let first = _callbackList[0];
+    const first = _callbackList[0];
 
     if (!first) {
         debuglog("_scheduleRealCallback: no more callbacks, not rescheduling");
         return;
     }
 
-    let now = _now();
-    let delayMs = Math.min(first.runAt - now, TIMER_CHECK_PERIOD_MS);
+    const now = _now();
+    const delayMs = Math.min(first.runAt - now, TIMER_CHECK_PERIOD_MS);
 
     debuglog("_scheduleRealCallback: now:", now, "delay:", delayMs);
     _realCallbackKey = global.setTimeout(_runCallbacks, delayMs);
@@ -145,13 +145,13 @@ function _scheduleRealCallback() {
 
 function _runCallbacks() {
     let cb;
-    let now = _now();
+    const now = _now();
     debuglog("_runCallbacks: now:", now);
 
     // get the list of things to call
-    let callbacksToRun = [];
+    const callbacksToRun = [];
     while (true) {
-        let first = _callbackList[0];
+        const first = _callbackList[0];
         if (!first || first.runAt > now) {
             break;
         }
@@ -188,8 +188,8 @@ function binarySearch(array, func) {
         max = array.length;
 
     while (min < max) {
-        let mid = (min + max) >> 1;
-        let res = func(array[mid]);
+        const mid = (min + max) >> 1;
+        const res = func(array[mid]);
         if (res > 0) {
             // the element at 'mid' is too big; set it as the new max.
             max = mid;
diff --git a/src/scheduler.js b/src/scheduler.js
index de77524bb..d3b454470 100644
--- a/src/scheduler.js
+++ b/src/scheduler.js
@@ -19,10 +19,10 @@ limitations under the License.
  * of requests.
  * @module scheduler
  */
-let utils = require("./utils");
-let q = require("q");
+const utils = require("./utils");
+const q = require("q");
 
-let DEBUG = false;  // set true to enable console logging.
+const DEBUG = false;  // set true to enable console logging.
 
 /**
  * Construct a scheduler for Matrix. Requires
@@ -60,7 +60,7 @@ function MatrixScheduler(retryAlgorithm, queueAlgorithm) {
  * @see MatrixScheduler.removeEventFromQueue To remove an event from the queue.
  */
 MatrixScheduler.prototype.getQueueForEvent = function(event) {
-    let name = this.queueAlgorithm(event);
+    const name = this.queueAlgorithm(event);
     if (!name || !this._queues[name]) {
         return null;
     }
@@ -76,7 +76,7 @@ MatrixScheduler.prototype.getQueueForEvent = function(event) {
  * @return {boolean} True if this event was removed.
  */
 MatrixScheduler.prototype.removeEventFromQueue = function(event) {
-    let name = this.queueAlgorithm(event);
+    const name = this.queueAlgorithm(event);
     if (!name || !this._queues[name]) {
         return false;
     }
@@ -110,7 +110,7 @@ MatrixScheduler.prototype.setProcessFunction = function(fn) {
  * resolved or rejected in due time, else null.
  */
 MatrixScheduler.prototype.queueEvent = function(event) {
-    let queueName = this.queueAlgorithm(event);
+    const queueName = this.queueAlgorithm(event);
     if (!queueName) {
         return null;
     }
@@ -118,7 +118,7 @@ MatrixScheduler.prototype.queueEvent = function(event) {
     if (!this._queues[queueName]) {
         this._queues[queueName] = [];
     }
-    let defer = q.defer();
+    const defer = q.defer();
     this._queues[queueName].push({
         event: event,
         defer: defer,
@@ -155,7 +155,7 @@ MatrixScheduler.RETRY_BACKOFF_RATELIMIT = function(event, attempts, err) {
     }
 
     if (err.name === "M_LIMIT_EXCEEDED") {
-        let waitTime = err.data.retry_after_ms;
+        const waitTime = err.data.retry_after_ms;
         if (waitTime) {
             return waitTime;
         }
@@ -201,10 +201,10 @@ function _startProcessingQueues(scheduler) {
 
 function _processQueue(scheduler, queueName) {
     // get head of queue
-    let obj = _peekNextEvent(scheduler, queueName);
+    const obj = _peekNextEvent(scheduler, queueName);
     if (!obj) {
         // queue is empty. Mark as inactive and stop recursing.
-        let index = scheduler._activeQueues.indexOf(queueName);
+        const index = scheduler._activeQueues.indexOf(queueName);
         if (index >= 0) {
             scheduler._activeQueues.splice(index, 1);
         }
@@ -227,7 +227,7 @@ function _processQueue(scheduler, queueName) {
     }, function(err) {
         obj.attempts += 1;
         // ask the retry algorithm when/if we should try again
-        let waitTimeMs = scheduler.retryAlgorithm(obj.event, obj.attempts, err);
+        const waitTimeMs = scheduler.retryAlgorithm(obj.event, obj.attempts, err);
         debuglog(
             "retry(%s) err=%s event_id=%s waitTime=%s",
             obj.attempts, err, obj.event.getId(), waitTimeMs
@@ -250,7 +250,7 @@ function _processQueue(scheduler, queueName) {
 }
 
 function _peekNextEvent(scheduler, queueName) {
-    let queue = scheduler._queues[queueName];
+    const queue = scheduler._queues[queueName];
     if (!utils.isArray(queue)) {
         return null;
     }
@@ -258,7 +258,7 @@ function _peekNextEvent(scheduler, queueName) {
 }
 
 function _removeNextEvent(scheduler, queueName) {
-    let queue = scheduler._queues[queueName];
+    const queue = scheduler._queues[queueName];
     if (!utils.isArray(queue)) {
         return null;
     }
diff --git a/src/store/memory.js b/src/store/memory.js
index c91651efa..71015b579 100644
--- a/src/store/memory.js
+++ b/src/store/memory.js
@@ -18,8 +18,8 @@ limitations under the License.
  * This is an internal module. See {@link MatrixInMemoryStore} for the public class.
  * @module store/memory
  */
- let utils = require("../utils");
- let User = require("../models/user");
+ const utils = require("../utils");
+ const User = require("../models/user");
 
 /**
  * Construct a new in-memory data store for the Matrix Client.
@@ -77,7 +77,7 @@ module.exports.MatrixInMemoryStore.prototype = {
         // map up-to-date.
         room.currentState.on("RoomState.members", this._onRoomMember.bind(this));
         // add existing members
-        let self = this;
+        const self = this;
         room.currentState.getMembers().forEach(function(m) {
             self._onRoomMember(null, room.currentState, m);
         });
@@ -97,7 +97,7 @@ module.exports.MatrixInMemoryStore.prototype = {
             return;
         }
 
-        let user = this.users[member.userId] || new User(member.userId);
+        const user = this.users[member.userId] || new User(member.userId);
         if (member.name) {
             user.setDisplayName(member.name);
             if (member.events.member) {
@@ -260,7 +260,7 @@ module.exports.MatrixInMemoryStore.prototype = {
      * @param {Array<MatrixEvent>} events The events to store.
      */
     storeAccountDataEvents: function(events) {
-        let self = this;
+        const self = this;
         events.forEach(function(event) {
             self.accountData[event.getType()] = event;
         });
diff --git a/src/store/session/webstorage.js b/src/store/session/webstorage.js
index 2e1e52a23..410adda19 100644
--- a/src/store/session/webstorage.js
+++ b/src/store/session/webstorage.js
@@ -19,10 +19,10 @@ limitations under the License.
  * @module store/session/webstorage
  */
 
-let utils = require("../../utils");
+const utils = require("../../utils");
 
-let DEBUG = false;  // set true to enable console logging.
-let E2E_PREFIX = "session.e2e.";
+const DEBUG = false;  // set true to enable console logging.
+const E2E_PREFIX = "session.e2e.";
 
 /**
  * Construct a web storage session store, capable of storing account keys,
@@ -106,7 +106,7 @@ WebStorageSessionStore.prototype = {
      * @param {string} session Base64 encoded end-to-end session.
      */
     storeEndToEndSession: function(deviceKey, sessionId, session) {
-        let sessions = this.getEndToEndSessions(deviceKey) || {};
+        const sessions = this.getEndToEndSessions(deviceKey) || {};
         sessions[sessionId] = session;
         setJsonItem(
             this.store, keyEndToEndSessions(deviceKey), sessions
@@ -150,12 +150,12 @@ WebStorageSessionStore.prototype = {
     },
 
     getEndToEndInboundGroupSession: function(senderKey, sessionId) {
-        let key = keyEndToEndInboundGroupSession(senderKey, sessionId);
+        const key = keyEndToEndInboundGroupSession(senderKey, sessionId);
         return this.store.getItem(key);
     },
 
     storeEndToEndInboundGroupSession: function(senderKey, sessionId, pickledSession) {
-        let key = keyEndToEndInboundGroupSession(senderKey, sessionId);
+        const key = keyEndToEndInboundGroupSession(senderKey, sessionId);
         return this.store.setItem(key, pickledSession);
     },
 
@@ -178,8 +178,8 @@ WebStorageSessionStore.prototype = {
     },
 };
 
-let KEY_END_TO_END_ACCOUNT = E2E_PREFIX + "account";
-let KEY_END_TO_END_ANNOUNCED = E2E_PREFIX + "announced";
+const KEY_END_TO_END_ACCOUNT = E2E_PREFIX + "account";
+const KEY_END_TO_END_ANNOUNCED = E2E_PREFIX + "announced";
 
 function keyEndToEndDevicesForUser(userId) {
     return E2E_PREFIX + "devices/" + userId;
diff --git a/src/sync.js b/src/sync.js
index f0a00eb20..a7da42353 100644
--- a/src/sync.js
+++ b/src/sync.js
@@ -23,20 +23,20 @@ limitations under the License.
  * an alternative syncing API, we may want to have a proper syncing interface
  * for HTTP and WS at some point.
  */
-let q = require("q");
-let User = require("./models/user");
-let Room = require("./models/room");
-let utils = require("./utils");
-let Filter = require("./filter");
-let EventTimeline = require("./models/event-timeline");
+const q = require("q");
+const User = require("./models/user");
+const Room = require("./models/room");
+const utils = require("./utils");
+const Filter = require("./filter");
+const EventTimeline = require("./models/event-timeline");
 
-let DEBUG = true;
+const DEBUG = true;
 
 // /sync requests allow you to set a timeout= but the request may continue
 // beyond that and wedge forever, so we need to track how long we are willing
 // to keep open the connection. This constant is *ADDED* to the timeout= value
 // to determine the max time we're willing to wait.
-let BUFFER_PERIOD_MS = 80 * 1000;
+const BUFFER_PERIOD_MS = 80 * 1000;
 
 function getFilterName(userId, suffix) {
     // scope this on the user ID because people may login on many accounts
@@ -88,8 +88,8 @@ function SyncApi(client, opts) {
  * @return {Room}
  */
 SyncApi.prototype.createRoom = function(roomId) {
-    let client = this.client;
-    let room = new Room(roomId, {
+    const client = this.client;
+    const room = new Room(roomId, {
         pendingEventOrdering: this.opts.pendingEventOrdering,
         timelineSupport: client.timelineSupport,
     });
@@ -108,7 +108,7 @@ SyncApi.prototype.createRoom = function(roomId) {
  * @private
  */
 SyncApi.prototype._registerStateListeners = function(room) {
-    let client = this.client;
+    const client = this.client;
     // we need to also re-emit room state and room member events, so hook it up
     // to the client now. We need to add a listener for RoomState.members in
     // order to hook them correctly. (TODO: find a better way?)
@@ -144,16 +144,16 @@ SyncApi.prototype._deregisterStateListeners = function(room) {
  * @return {Promise} Resolved when they've been added to the store.
  */
 SyncApi.prototype.syncLeftRooms = function() {
-    let client = this.client;
-    let self = this;
+    const client = this.client;
+    const self = this;
 
     // grab a filter with limit=1 and include_leave=true
-    let filter = new Filter(this.client.credentials.userId);
+    const filter = new Filter(this.client.credentials.userId);
     filter.setTimelineLimit(1);
     filter.setIncludeLeaveRooms(true);
 
-    let localTimeoutMs = this.opts.pollTimeout + BUFFER_PERIOD_MS;
-    let qps = {
+    const localTimeoutMs = this.opts.pollTimeout + BUFFER_PERIOD_MS;
+    const qps = {
         timeout: 0, // don't want to block since this is a single isolated req
     };
 
@@ -169,9 +169,9 @@ SyncApi.prototype.syncLeftRooms = function() {
         if (data.rooms && data.rooms.leave) {
             leaveRooms = self._mapSyncResponseToRoomArray(data.rooms.leave);
         }
-        let rooms = [];
+        const rooms = [];
         leaveRooms.forEach(function(leaveObj) {
-            let room = leaveObj.room;
+            const room = leaveObj.room;
             rooms.push(room);
             if (!leaveObj.isBrandNewRoom) {
                 // the intention behind syncLeftRooms is to add in rooms which were
@@ -185,9 +185,9 @@ SyncApi.prototype.syncLeftRooms = function() {
                 return;
             }
             leaveObj.timeline = leaveObj.timeline || {};
-            let timelineEvents =
+            const timelineEvents =
                 self._mapSyncEventsFormat(leaveObj.timeline, room);
-            let stateEvents = self._mapSyncEventsFormat(leaveObj.state, room);
+            const stateEvents = self._mapSyncEventsFormat(leaveObj.state, room);
 
             // set the back-pagination token. Do this *before* adding any
             // events so that clients can start back-paginating.
@@ -212,8 +212,8 @@ SyncApi.prototype.syncLeftRooms = function() {
  * store.
  */
 SyncApi.prototype.peek = function(roomId) {
-    let self = this;
-    let client = this.client;
+    const self = this;
+    const client = this.client;
     this._peekRoomId = roomId;
     return this.client.roomInitialSync(roomId, 20).then(function(response) {
         // make sure things are init'd
@@ -221,17 +221,17 @@ SyncApi.prototype.peek = function(roomId) {
         response.messages.chunk = response.messages.chunk || [];
         response.state = response.state || [];
 
-        let peekRoom = self.createRoom(roomId);
+        const peekRoom = self.createRoom(roomId);
 
         // FIXME: Mostly duplicated from _processRoomEvents but not entirely
         // because "state" in this API is at the BEGINNING of the chunk
-        let oldStateEvents = utils.map(
+        const oldStateEvents = utils.map(
             utils.deepCopy(response.state), client.getEventMapper()
         );
-        let stateEvents = utils.map(
+        const stateEvents = utils.map(
             response.state, client.getEventMapper()
         );
-        let messages = utils.map(
+        const messages = utils.map(
             response.messages.chunk, client.getEventMapper()
         );
 
@@ -301,7 +301,7 @@ SyncApi.prototype._peekPoll = function(roomId, token) {
         return;
     }
 
-    let self = this;
+    const self = this;
     // FIXME: gut wrenching; hard-coded timeout values
     this.client._http.authedRequest(undefined, "GET", "/events", {
         room_id: roomId,
@@ -332,10 +332,10 @@ SyncApi.prototype._peekPoll = function(roomId, token) {
         });
 
         // strip out events which aren't for the given room_id (e.g presence)
-        let events = res.chunk.filter(function(e) {
+        const events = res.chunk.filter(function(e) {
             return e.room_id === roomId;
         }).map(self.client.getEventMapper());
-        let room = self.client.getRoom(roomId);
+        const room = self.client.getRoom(roomId);
         room.addLiveEvents(events);
         self._peekPoll(roomId, res.end);
     }, function(err) {
@@ -362,8 +362,8 @@ SyncApi.prototype.sync = function() {
     debuglog("SyncApi.sync: starting with sync token " +
              this.client.store.getSyncToken());
 
-    let client = this.client;
-    let self = this;
+    const client = this.client;
+    const self = this;
 
     this._running = true;
 
@@ -465,8 +465,8 @@ SyncApi.prototype.retryImmediately = function() {
  * @param {boolean} syncOptions.hasSyncedBefore
  */
 SyncApi.prototype._sync = function(syncOptions) {
-    let client = this.client;
-    let self = this;
+    const client = this.client;
+    const self = this;
 
     if (!this._running) {
         debuglog("Sync no longer running: exiting.");
@@ -483,9 +483,9 @@ SyncApi.prototype._sync = function(syncOptions) {
         filterId = this._getGuestFilter();
     }
 
-    let syncToken = client.store.getSyncToken();
+    const syncToken = client.store.getSyncToken();
 
-    let qps = {
+    const qps = {
         filter: filterId,
         timeout: this.opts.pollTimeout,
     };
@@ -508,7 +508,7 @@ SyncApi.prototype._sync = function(syncOptions) {
     }
 
     // normal timeout= plus buffer time
-    let clientSideTimeoutMs = this.opts.pollTimeout + BUFFER_PERIOD_MS;
+    const clientSideTimeoutMs = this.opts.pollTimeout + BUFFER_PERIOD_MS;
 
     this._currentSyncRequest = client._http.authedRequest(
         undefined, "GET", "/sync", qps, undefined, clientSideTimeoutMs
@@ -576,8 +576,8 @@ SyncApi.prototype._sync = function(syncOptions) {
  * @param {Object} data The response from /sync
  */
 SyncApi.prototype._processSyncResponse = function(syncToken, data) {
-    let client = this.client;
-    let self = this;
+    const client = this.client;
+    const self = this;
 
     // data looks like:
     // {
@@ -635,7 +635,7 @@ SyncApi.prototype._processSyncResponse = function(syncToken, data) {
 
     // handle non-room account_data
     if (data.account_data && utils.isArray(data.account_data.events)) {
-        let events = data.account_data.events.map(client.getEventMapper());
+        const events = data.account_data.events.map(client.getEventMapper());
         client.store.storeAccountDataEvents(events);
         events.forEach(
             function(accountDataEvent) {
@@ -654,7 +654,7 @@ SyncApi.prototype._processSyncResponse = function(syncToken, data) {
             .map(client.getEventMapper())
             .forEach(
                 function(toDeviceEvent) {
-                    let content = toDeviceEvent.getContent();
+                    const content = toDeviceEvent.getContent();
                     if (
                         toDeviceEvent.getType() == "m.room.message" &&
                             content.msgtype == "m.bad.encrypted"
@@ -693,8 +693,8 @@ SyncApi.prototype._processSyncResponse = function(syncToken, data) {
 
     // Handle invites
     inviteRooms.forEach(function(inviteObj) {
-        let room = inviteObj.room;
-        let stateEvents =
+        const room = inviteObj.room;
+        const stateEvents =
             self._mapSyncEventsFormat(inviteObj.invite_state, room);
         self._processRoomEvents(room, stateEvents);
         if (inviteObj.isBrandNewRoom) {
@@ -709,11 +709,11 @@ SyncApi.prototype._processSyncResponse = function(syncToken, data) {
 
     // Handle joins
     joinRooms.forEach(function(joinObj) {
-        let room = joinObj.room;
-        let stateEvents = self._mapSyncEventsFormat(joinObj.state, room);
-        let timelineEvents = self._mapSyncEventsFormat(joinObj.timeline, room);
-        let ephemeralEvents = self._mapSyncEventsFormat(joinObj.ephemeral);
-        let accountDataEvents = self._mapSyncEventsFormat(joinObj.account_data);
+        const room = joinObj.room;
+        const stateEvents = self._mapSyncEventsFormat(joinObj.state, room);
+        const timelineEvents = self._mapSyncEventsFormat(joinObj.timeline, room);
+        const ephemeralEvents = self._mapSyncEventsFormat(joinObj.ephemeral);
+        const accountDataEvents = self._mapSyncEventsFormat(joinObj.account_data);
 
         // we do this first so it's correct when any of the events fire
         if (joinObj.unread_notifications) {
@@ -748,7 +748,7 @@ SyncApi.prototype._processSyncResponse = function(syncToken, data) {
             // will stop us linking the empty timeline into the chain).
             //
             for (let i = timelineEvents.length - 1; i >= 0; i--) {
-                let eventId = timelineEvents[i].getId();
+                const eventId = timelineEvents[i].getId();
                 if (room.getTimelineForEvent(eventId)) {
                     debuglog("Already have event " + eventId + " in limited " +
                              "sync - not resetting");
@@ -818,12 +818,12 @@ SyncApi.prototype._processSyncResponse = function(syncToken, data) {
 
     // Handle leaves (e.g. kicked rooms)
     leaveRooms.forEach(function(leaveObj) {
-        let room = leaveObj.room;
-        let stateEvents =
+        const room = leaveObj.room;
+        const stateEvents =
             self._mapSyncEventsFormat(leaveObj.state, room);
-        let timelineEvents =
+        const timelineEvents =
             self._mapSyncEventsFormat(leaveObj.timeline, room);
-        let accountDataEvents =
+        const accountDataEvents =
             self._mapSyncEventsFormat(leaveObj.account_data);
 
         self._processRoomEvents(room, stateEvents, timelineEvents);
@@ -876,7 +876,7 @@ SyncApi.prototype._startKeepAlives = function(delay) {
     if (this._keepAliveTimer !== null) {
         clearTimeout(this._keepAliveTimer);
     }
-    let self = this;
+    const self = this;
     if (delay > 0) {
         self._keepAliveTimer = setTimeout(
             self._pokeKeepAlive.bind(self),
@@ -895,7 +895,7 @@ SyncApi.prototype._startKeepAlives = function(delay) {
  *
  */
 SyncApi.prototype._pokeKeepAlive = function() {
-    let self = this;
+    const self = this;
     function success() {
         clearTimeout(self._keepAliveTimer);
         if (self._connectionReturnedDefer) {
@@ -947,10 +947,10 @@ SyncApi.prototype._mapSyncResponseToRoomArray = function(obj) {
     // Maps { roomid: {stuff}, roomid: {stuff} }
     // to
     // [{stuff+Room+isBrandNewRoom}, {stuff+Room+isBrandNewRoom}]
-    let client = this.client;
-    let self = this;
+    const client = this.client;
+    const self = this;
     return utils.keys(obj).map(function(roomId) {
-        let arrObj = obj[roomId];
+        const arrObj = obj[roomId];
         let room = client.store.getRoom(roomId);
         let isBrandNewRoom = false;
         if (!room) {
@@ -972,7 +972,7 @@ SyncApi.prototype._mapSyncEventsFormat = function(obj, room) {
     if (!obj || !utils.isArray(obj.events)) {
         return [];
     }
-    let mapper = this.client.getEventMapper();
+    const mapper = this.client.getEventMapper();
     return obj.events.map(function(e) {
         if (room) {
             e.room_id = room.roomId;
@@ -988,7 +988,7 @@ SyncApi.prototype._resolveInvites = function(room) {
     if (!room || !this.opts.resolveInvitesToProfiles) {
         return;
     }
-    let client = this.client;
+    const client = this.client;
     // For each invited room member we want to give them a displayname/avatar url
     // if they have one (the m.room.member invites don't contain this).
     room.getMembersWithMembership("invite").forEach(function(member) {
@@ -997,7 +997,7 @@ SyncApi.prototype._resolveInvites = function(room) {
         }
         member._requestedProfileInfo = true;
         // try to get a cached copy first.
-        let user = client.getUser(member.userId);
+        const user = client.getUser(member.userId);
         let promise;
         if (user) {
             promise = q({
@@ -1011,7 +1011,7 @@ SyncApi.prototype._resolveInvites = function(room) {
             // slightly naughty by doctoring the invite event but this means all
             // the code paths remain the same between invite/join display name stuff
             // which is a worthy trade-off for some minor pollution.
-            let inviteEvent = member.events.member;
+            const inviteEvent = member.events.member;
             if (inviteEvent.getContent().membership !== "invite") {
                 // between resolving and now they have since joined, so don't clobber
                 return;
@@ -1036,19 +1036,19 @@ SyncApi.prototype._resolveInvites = function(room) {
 SyncApi.prototype._processRoomEvents = function(room, stateEventList,
                                                 timelineEventList) {
     timelineEventList = timelineEventList || [];
-    let client = this.client;
+    const client = this.client;
     // "old" and "current" state are the same initially; they
     // start diverging if the user paginates.
     // We must deep copy otherwise membership changes in old state
     // will leak through to current state!
-    let oldStateEvents = utils.map(
+    const oldStateEvents = utils.map(
         utils.deepCopy(
             stateEventList.map(function(mxEvent) {
                 return mxEvent.event;
             })
         ), client.getEventMapper()
     );
-    let stateEvents = stateEventList;
+    const stateEvents = stateEventList;
 
     // set the state of the room to as it was before the timeline executes
     //
@@ -1068,7 +1068,7 @@ SyncApi.prototype._processRoomEvents = function(room, stateEventList,
     // gather our notifications into this._notifEvents
     if (client.getNotifTimelineSet()) {
         for (let i = 0; i < timelineEventList.length; i++) {
-            let pushActions = client.getPushActionsForEvent(timelineEventList[i]);
+            const pushActions = client.getPushActionsForEvent(timelineEventList[i]);
             if (pushActions && pushActions.notify &&
                 pushActions.tweaks && pushActions.tweaks.highlight) {
                 this._notifEvents.push(timelineEventList[i]);
@@ -1085,7 +1085,7 @@ SyncApi.prototype._processRoomEvents = function(room, stateEventList,
  * @return {string}
  */
 SyncApi.prototype._getGuestFilter = function() {
-    let guestRooms = this.client._guestRooms; // FIXME: horrible gut-wrenching
+    const guestRooms = this.client._guestRooms; // FIXME: horrible gut-wrenching
     if (!guestRooms) {
         return "{}";
     }
@@ -1106,7 +1106,7 @@ SyncApi.prototype._getGuestFilter = function() {
  * @param {Object} data Object of additional data to emit in the event
  */
 SyncApi.prototype._updateSyncState = function(newState, data) {
-    let old = this._syncState;
+    const old = this._syncState;
     this._syncState = newState;
     this.client.emit("sync", this._syncState, old, data);
 };
@@ -1123,7 +1123,7 @@ SyncApi.prototype._onOnline = function() {
 };
 
 function createNewUser(client, userId) {
-    let user = new User(userId);
+    const user = new User(userId);
     reEmit(client, user, [
         "User.avatarUrl", "User.displayName", "User.presence",
         "User.currentlyActive", "User.lastPresenceTs",
@@ -1140,7 +1140,7 @@ function reEmit(reEmitEntity, emittableEntity, eventNames) {
             // Transformation Example:
             // listener on "foo" => function(a,b) { ... }
             // Re-emit on "thing" => thing.emit("foo", a, b)
-            let newArgs = [eventName];
+            const newArgs = [eventName];
             for (let i = 0; i < arguments.length; i++) {
                 newArgs.push(arguments[i]);
             }
diff --git a/src/timeline-window.js b/src/timeline-window.js
index 72d7ca431..523f8fcda 100644
--- a/src/timeline-window.js
+++ b/src/timeline-window.js
@@ -17,25 +17,25 @@ limitations under the License.
 
 /** @module timeline-window */
 
-let q = require("q");
-let EventTimeline = require("./models/event-timeline");
+const q = require("q");
+const EventTimeline = require("./models/event-timeline");
 
 /**
  * @private
  */
-let DEBUG = false;
+const DEBUG = false;
 
 /**
  * @private
  */
-let debuglog = DEBUG ? console.log.bind(console) : function() {};
+const debuglog = DEBUG ? console.log.bind(console) : function() {};
 
 /**
  * the number of times we ask the server for more events before giving up
  *
  * @private
  */
-let DEFAULT_PAGINATE_LOOP_LIMIT = 5;
+const DEFAULT_PAGINATE_LOOP_LIMIT = 5;
 
 /**
  * Construct a TimelineWindow.
@@ -92,15 +92,15 @@ function TimelineWindow(client, timelineSet, opts) {
  * @return {module:client.Promise}
  */
 TimelineWindow.prototype.load = function(initialEventId, initialWindowSize) {
-    let self = this;
+    const self = this;
     initialWindowSize = initialWindowSize || 20;
 
     // given an EventTimeline, and an event index within it, initialise our
     // fields so that the event in question is in the middle of the window.
-    let initFields = function(timeline, eventIndex) {
-        let endIndex = Math.min(timeline.getEvents().length,
+    const initFields = function(timeline, eventIndex) {
+        const endIndex = Math.min(timeline.getEvents().length,
                                 eventIndex + Math.ceil(initialWindowSize / 2));
-        let startIndex = Math.max(0, endIndex - initialWindowSize);
+        const startIndex = Math.max(0, endIndex - initialWindowSize);
         self._start = new TimelineIndex(timeline, startIndex - timeline.getBaseIndex());
         self._end = new TimelineIndex(timeline, endIndex - timeline.getBaseIndex());
         self._eventCount = endIndex - startIndex;
@@ -126,7 +126,7 @@ TimelineWindow.prototype.load = function(initialEventId, initialWindowSize) {
             });
     } else {
         // start with the most recent events
-        let tl = this._timelineSet.getLiveTimeline();
+        const tl = this._timelineSet.getLiveTimeline();
         initFields(tl, tl.getEvents().length);
         return q();
     }
@@ -228,7 +228,7 @@ TimelineWindow.prototype.paginate = function(direction, size, makeRequest,
     }
 
     // try moving the cap
-    let count = (direction == EventTimeline.BACKWARDS) ?
+    const count = (direction == EventTimeline.BACKWARDS) ?
         tl.retreat(size) : tl.advance(size);
 
     if (count) {
@@ -236,7 +236,7 @@ TimelineWindow.prototype.paginate = function(direction, size, makeRequest,
         debuglog("TimelineWindow: increased cap by " + count +
                  " (now " + this._eventCount + ")");
         // remove some events from the other end, if necessary
-        let excess = this._eventCount - this._windowLimit;
+        const excess = this._eventCount - this._windowLimit;
         if (excess > 0) {
             this.unpaginate(excess, direction != EventTimeline.BACKWARDS);
         }
@@ -250,16 +250,16 @@ TimelineWindow.prototype.paginate = function(direction, size, makeRequest,
     }
 
     // try making a pagination request
-    let token = tl.timeline.getPaginationToken(direction);
+    const token = tl.timeline.getPaginationToken(direction);
     if (!token) {
         debuglog("TimelineWindow: no token");
         return q(false);
     }
 
     debuglog("TimelineWindow: starting request");
-    let self = this;
+    const self = this;
 
-    let prom = this._client.paginateEventTimeline(tl.timeline, {
+    const prom = this._client.paginateEventTimeline(tl.timeline, {
         backwards: direction == EventTimeline.BACKWARDS,
         limit: size,
     }).finally(function() {
@@ -298,7 +298,7 @@ TimelineWindow.prototype.paginate = function(direction, size, makeRequest,
  *     of the timeline.
  */
 TimelineWindow.prototype.unpaginate = function(delta, startOfTimeline) {
-    let tl = startOfTimeline ? this._start : this._end;
+    const tl = startOfTimeline ? this._start : this._end;
 
     // sanity-check the delta
     if (delta > this._eventCount || delta < 0) {
@@ -307,7 +307,7 @@ TimelineWindow.prototype.unpaginate = function(delta, startOfTimeline) {
     }
 
     while (delta > 0) {
-        let count = startOfTimeline ? tl.advance(delta) : tl.retreat(delta);
+        const count = startOfTimeline ? tl.advance(delta) : tl.retreat(delta);
         if (count <= 0) {
             // sadness. This shouldn't be possible.
             throw new Error(
@@ -334,13 +334,13 @@ TimelineWindow.prototype.getEvents = function() {
         return [];
     }
 
-    let result = [];
+    const result = [];
 
     // iterate through each timeline between this._start and this._end
     // (inclusive).
     let timeline = this._start.timeline;
     while (true) {
-        let events = timeline.getEvents();
+        const events = timeline.getEvents();
 
         // For the first timeline in the chain, we want to start at
         // this._start.index. For the last timeline in the chain, we want to
@@ -447,7 +447,7 @@ TimelineIndex.prototype.advance = function(delta) {
     // the index is already at the start/end of the current timeline.
     //
     // next see if there is a neighbouring timeline to switch to.
-    let neighbour = this.timeline.getNeighbouringTimeline(
+    const neighbour = this.timeline.getNeighbouringTimeline(
         delta < 0 ? EventTimeline.BACKWARDS : EventTimeline.FORWARDS);
     if (neighbour) {
         this.timeline = neighbour;
diff --git a/src/utils.js b/src/utils.js
index 8f13716f8..662dee619 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -27,7 +27,7 @@ limitations under the License.
  */
 module.exports.encodeParams = function(params) {
     let qs = "";
-    for (let key in params) {
+    for (const key in params) {
         if (!params.hasOwnProperty(key)) {
             continue;
         }
@@ -46,7 +46,7 @@ module.exports.encodeParams = function(params) {
  * @return {string} The result of replacing all template variables e.g. '/foo/baz'.
  */
 module.exports.encodeUri = function(pathTemplate, variables) {
-    for (let key in variables) {
+    for (const key in variables) {
         if (!variables.hasOwnProperty(key)) {
             continue;
         }
@@ -65,7 +65,7 @@ module.exports.encodeUri = function(pathTemplate, variables) {
  * @return {Array} A new array with the results of the function.
  */
 module.exports.map = function(array, fn) {
-    let results = new Array(array.length);
+    const results = new Array(array.length);
     for (let i = 0; i < array.length; i++) {
         results[i] = fn(array[i]);
     }
@@ -81,7 +81,7 @@ module.exports.map = function(array, fn) {
  * @return {Array} A new array with the results of the function.
  */
 module.exports.filter = function(array, fn) {
-    let results = [];
+    const results = [];
     for (let i = 0; i < array.length; i++) {
         if (fn(array[i], i, array)) {
             results.push(array[i]);
@@ -96,8 +96,8 @@ module.exports.filter = function(array, fn) {
  * @return {string[]} The keys of the object.
  */
 module.exports.keys = function(obj) {
-    let keys = [];
-    for (let key in obj) {
+    const keys = [];
+    for (const key in obj) {
         if (!obj.hasOwnProperty(key)) {
             continue;
         }
@@ -112,8 +112,8 @@ module.exports.keys = function(obj) {
  * @return {Array<*>} The values of the object.
  */
 module.exports.values = function(obj) {
-    let values = [];
-    for (let key in obj) {
+    const values = [];
+    for (const key in obj) {
         if (!obj.hasOwnProperty(key)) {
             continue;
         }
@@ -235,7 +235,7 @@ module.exports.checkObjectHasKeys = function(obj, keys) {
  * @throws If there are extra keys.
  */
 module.exports.checkObjectHasNoAdditionalKeys = function(obj, allowedKeys) {
-    for (let key in obj) {
+    for (const key in obj) {
         if (!obj.hasOwnProperty(key)) {
             continue;
         }
@@ -263,7 +263,7 @@ module.exports.deepCopy = function(obj) {
  *
  * @return {boolean} true if the two objects are equal
  */
-let deepCompare = module.exports.deepCompare = function(x, y) {
+const deepCompare = module.exports.deepCompare = function(x, y) {
     // Inspired by
     // http://stackoverflow.com/questions/1068834/object-comparison-in-javascript#1144249
 
@@ -355,10 +355,10 @@ let deepCompare = module.exports.deepCompare = function(x, y) {
  * @return {Object} target
  */
 module.exports.extend = function() {
-    let target = arguments[0] || {};
+    const target = arguments[0] || {};
     for (let i = 1; i < arguments.length; i++) {
-        let source = arguments[i];
-        for (let propName in source) { // eslint-disable-line guard-for-in
+        const source = arguments[i];
+        for (const propName in source) { // eslint-disable-line guard-for-in
             target[propName] = source[propName];
         }
     }
@@ -379,17 +379,17 @@ module.exports.runPolyfills = function() {
           throw new TypeError();
         }
 
-        let t = Object(this);
-        let len = t.length >>> 0;
+        const t = Object(this);
+        const len = t.length >>> 0;
         if (typeof fun !== 'function') {
           throw new TypeError();
         }
 
-        let res = [];
-        let thisArg = arguments.length >= 2 ? arguments[1] : void 0;
+        const res = [];
+        const thisArg = arguments.length >= 2 ? arguments[1] : void 0;
         for (let i = 0; i < len; i++) {
           if (i in t) {
-            let val = t[i];
+            const val = t[i];
 
             // NOTE: Technically this should Object.defineProperty at
             //       the next index, as push can be affected by
@@ -422,12 +422,12 @@ module.exports.runPolyfills = function() {
 
         // 1. Let O be the result of calling ToObject passing the |this|
         //    value as the argument.
-        let O = Object(this);
+        const O = Object(this);
 
         // 2. Let lenValue be the result of calling the Get internal
         //    method of O with the argument "length".
         // 3. Let len be ToUint32(lenValue).
-        let len = O.length >>> 0;
+        const len = O.length >>> 0;
 
         // 4. If IsCallable(callback) is false, throw a TypeError exception.
         // See: http://es5.github.com/#x9.11
@@ -512,12 +512,12 @@ module.exports.runPolyfills = function() {
 
         // 1. Let O be the result of calling ToObject passing the |this| value as the
         // argument.
-        let O = Object(this);
+        const O = Object(this);
 
         // 2. Let lenValue be the result of calling the Get internal method of O with the
         // argument "length".
         // 3. Let len be ToUint32(lenValue).
-        let len = O.length >>> 0;
+        const len = O.length >>> 0;
 
         // 4. If IsCallable(callback) is false, throw a TypeError exception.
         // See: http://es5.github.com/#x9.11
@@ -582,7 +582,7 @@ module.exports.inherits = function(ctor, superCtor) {
         function Temp() {}
 
         // make a safe reference to Object.prototype.hasOwnProperty
-        let hasOwn = Object.prototype.hasOwnProperty;
+        const hasOwn = Object.prototype.hasOwnProperty;
 
         return function(O) {
           // 1. If Type(O) is not Object or Null throw a TypeError exception.
@@ -595,7 +595,7 @@ module.exports.inherits = function(ctor, superCtor) {
           //    constructor with that name
           // 3. Set the [[Prototype]] internal property of obj to O.
           Temp.prototype = O;
-          let obj = new Temp();
+          const obj = new Temp();
           Temp.prototype = null; // Let's not keep a stray reference to O...
 
           // 4. If the argument Properties is present and not undefined, add
@@ -604,8 +604,8 @@ module.exports.inherits = function(ctor, superCtor) {
           //    Properties.
           if (arguments.length > 1) {
             // Object.defineProperties does ToObject on its first argument.
-            let Properties = Object(arguments[1]);
-            for (let prop in Properties) {
+            const Properties = Object(arguments[1]);
+            for (const prop in Properties) {
               if (hasOwn.call(Properties, prop)) {
                 obj[prop] = Properties[prop];
               }
diff --git a/src/webrtc/call.js b/src/webrtc/call.js
index f730a2067..5e3111bd5 100644
--- a/src/webrtc/call.js
+++ b/src/webrtc/call.js
@@ -18,9 +18,9 @@ limitations under the License.
  * This is an internal module. See {@link createNewMatrixCall} for the public API.
  * @module webrtc/call
  */
-let utils = require("../utils");
-let EventEmitter = require("events").EventEmitter;
-let DEBUG = true;  // set true to enable console logging.
+const utils = require("../utils");
+const EventEmitter = require("events").EventEmitter;
+const DEBUG = true;  // set true to enable console logging.
 
 // events: hangup, error(err), replaced(call), state(state, oldState)
 
@@ -125,17 +125,17 @@ MatrixCall.prototype.placeScreenSharingCall =
     function(remoteVideoElement, localVideoElement) {
     debuglog("placeScreenSharingCall");
     checkForErrorListener(this);
-    let screenConstraints = _getChromeScreenSharingConstraints(this);
+    const screenConstraints = _getChromeScreenSharingConstraints(this);
     if (!screenConstraints) {
         return;
     }
     this.localVideoElement = localVideoElement;
     this.remoteVideoElement = remoteVideoElement;
-    let self = this;
+    const self = this;
     this.webRtc.getUserMedia(screenConstraints, function(stream) {
         self.screenSharingStream = stream;
         debuglog("Got screen stream, requesting audio stream...");
-        let audioConstraints = _getUserMediaVideoContraints('voice');
+        const audioConstraints = _getUserMediaVideoContraints('voice');
         _placeCallWithConstraints(self, audioConstraints);
     }, function(err) {
         self.emit("error",
@@ -266,9 +266,9 @@ MatrixCall.prototype.setLocalVideoElement = function(element) {
                            this.URL.createObjectURL(this.localAVStream),
                            "localVideo");
         element.muted = true;
-        let self = this;
+        const self = this;
         setTimeout(function() {
-            let vel = self.getLocalVideoElement();
+            const vel = self.getLocalVideoElement();
             if (vel.play) {
                 self.playElement(vel, "localVideo");
             }
@@ -306,7 +306,7 @@ MatrixCall.prototype.setRemoteAudioElement = function(element) {
 MatrixCall.prototype._initWithInvite = function(event) {
     this.msg = event.getContent();
     this.peerConn = _createPeerConnection(this);
-    let self = this;
+    const self = this;
     if (this.peerConn) {
         this.peerConn.setRemoteDescription(
             new this.webRtc.RtcSessionDescription(this.msg.offer),
@@ -364,7 +364,7 @@ MatrixCall.prototype._initWithHangup = function(event) {
  */
 MatrixCall.prototype.answer = function() {
     debuglog("Answering call %s of type %s", this.callId, this.type);
-    let self = this;
+    const self = this;
 
     if (!this.localAVStream && !this.waitForLocalAVStream) {
         this.webRtc.getUserMedia(
@@ -416,7 +416,7 @@ MatrixCall.prototype._replacedBy = function(newCall) {
 MatrixCall.prototype.hangup = function(reason, suppressEvent) {
     debuglog("Ending call " + this.callId);
     terminate(this, "local", reason, !suppressEvent);
-    let content = {
+    const content = {
         version: 0,
         call_id: this.callId,
         reason: reason,
@@ -492,8 +492,8 @@ MatrixCall.prototype._gotUserMediaForInvite = function(stream) {
         return;
     }
     debuglog("_gotUserMediaForInvite -> " + this.type);
-    let self = this;
-    let videoEl = this.getLocalVideoElement();
+    const self = this;
+    const videoEl = this.getLocalVideoElement();
 
     if (videoEl && this.type == 'video') {
         videoEl.autoplay = true;
@@ -509,7 +509,7 @@ MatrixCall.prototype._gotUserMediaForInvite = function(stream) {
         }
         videoEl.muted = true;
         setTimeout(function() {
-            let vel = self.getLocalVideoElement();
+            const vel = self.getLocalVideoElement();
             if (vel.play) {
                 self.playElement(vel, "localVideo");
             }
@@ -539,11 +539,11 @@ MatrixCall.prototype._gotUserMediaForInvite = function(stream) {
  * @param {Object} stream
  */
 MatrixCall.prototype._gotUserMediaForAnswer = function(stream) {
-    let self = this;
+    const self = this;
     if (self.state == 'ended') {
         return;
     }
-    let localVidEl = self.getLocalVideoElement();
+    const localVidEl = self.getLocalVideoElement();
 
     if (localVidEl && self.type == 'video') {
         localVidEl.autoplay = true;
@@ -552,7 +552,7 @@ MatrixCall.prototype._gotUserMediaForAnswer = function(stream) {
                "localVideo");
         localVidEl.muted = true;
         setTimeout(function() {
-            let vel = self.getLocalVideoElement();
+            const vel = self.getLocalVideoElement();
             if (vel.play) {
                 self.playElement(vel, "localVideo");
             }
@@ -563,7 +563,7 @@ MatrixCall.prototype._gotUserMediaForAnswer = function(stream) {
     setTracksEnabled(stream.getAudioTracks(), true);
     self.peerConn.addStream(stream);
 
-    let constraints = {
+    const constraints = {
         'mandatory': {
             'OfferToReceiveAudio': true,
             'OfferToReceiveVideo': self.type == 'video',
@@ -572,7 +572,7 @@ MatrixCall.prototype._gotUserMediaForAnswer = function(stream) {
     self.peerConn.createAnswer(function(description) {
         debuglog("Created answer: " + description);
         self.peerConn.setLocalDescription(description, function() {
-            let content = {
+            const content = {
                 version: 0,
                 call_id: self.callId,
                 answer: {
@@ -604,7 +604,7 @@ MatrixCall.prototype._gotLocalIceCandidate = function(event) {
         );
         // As with the offer, note we need to make a copy of this object, not
         // pass the original: that broke in Chrome ~m43.
-        let c = {
+        const c = {
             candidate: event.candidate.candidate,
             sdpMid: event.candidate.sdpMid,
             sdpMLineIndex: event.candidate.sdpMLineIndex,
@@ -641,7 +641,7 @@ MatrixCall.prototype._receivedAnswer = function(msg) {
         return;
     }
 
-    let self = this;
+    const self = this;
     this.peerConn.setRemoteDescription(
         new this.webRtc.RtcSessionDescription(msg.answer),
         hookCallback(self, self._onSetRemoteDescriptionSuccess),
@@ -656,7 +656,7 @@ MatrixCall.prototype._receivedAnswer = function(msg) {
  * @param {Object} description
  */
 MatrixCall.prototype._gotLocalOffer = function(description) {
-    let self = this;
+    const self = this;
     debuglog("Created offer: " + description);
 
     if (self.state == 'ended') {
@@ -666,7 +666,7 @@ MatrixCall.prototype._gotLocalOffer = function(description) {
     }
 
     self.peerConn.setLocalDescription(description, function() {
-        let content = {
+        const content = {
             version: 0,
             call_id: self.callId,
             // OpenWebRTC appears to add extra stuff (like the DTLS fingerprint)
@@ -784,7 +784,7 @@ MatrixCall.prototype._onSetRemoteDescriptionError = function(e) {
 MatrixCall.prototype._onAddStream = function(event) {
     debuglog("Stream id " + event.stream.id + " added");
 
-    let s = event.stream;
+    const s = event.stream;
 
     if (s.getVideoTracks().length > 0) {
         this.type = 'video';
@@ -795,7 +795,7 @@ MatrixCall.prototype._onAddStream = function(event) {
         this.remoteAStream = s;
     }
 
-    let self = this;
+    const self = this;
     forAllTracksOnStream(s, function(t) {
         debuglog("Track id " + t.id + " added");
         // not currently implemented in chrome
@@ -874,13 +874,13 @@ MatrixCall.prototype._onAnsweredElsewhere = function(msg) {
     terminate(this, "remote", "answered_elsewhere", true);
 };
 
-let setTracksEnabled = function(tracks, enabled) {
+const setTracksEnabled = function(tracks, enabled) {
     for (let i = 0; i < tracks.length; i++) {
         tracks[i].enabled = enabled;
     }
 };
 
-let isTracksEnabled = function(tracks) {
+const isTracksEnabled = function(tracks) {
     for (let i = 0; i < tracks.length; i++) {
         if (tracks[i].enabled) {
             return true; // at least one track is enabled
@@ -889,8 +889,8 @@ let isTracksEnabled = function(tracks) {
     return false;
 };
 
-let setState = function(self, state) {
-    let oldState = self.state;
+const setState = function(self, state) {
+    const oldState = self.state;
     self.state = state;
     self.emit("state", state, oldState);
 };
@@ -902,11 +902,11 @@ let setState = function(self, state) {
  * @param {Object} content
  * @return {Promise}
  */
-let sendEvent = function(self, eventType, content) {
+const sendEvent = function(self, eventType, content) {
     return self.client.sendEvent(self.roomId, eventType, content);
 };
 
-let sendCandidate = function(self, content) {
+const sendCandidate = function(self, content) {
     // Sends candidates with are sent in a special way because we try to amalgamate
     // them into one message
     self.candidateSendQueue.push(content);
@@ -917,7 +917,7 @@ let sendCandidate = function(self, content) {
     }
 };
 
-let terminate = function(self, hangupParty, hangupReason, shouldEmit) {
+const terminate = function(self, hangupParty, hangupReason, shouldEmit) {
     if (self.getRemoteVideoElement()) {
         if (self.getRemoteVideoElement().pause) {
             self.pauseElement(self.getRemoteVideoElement(), "remoteVideo");
@@ -948,7 +948,7 @@ let terminate = function(self, hangupParty, hangupReason, shouldEmit) {
     }
 };
 
-let stopAllMedia = function(self) {
+const stopAllMedia = function(self) {
     debuglog("stopAllMedia (stream=%s)", self.localAVStream);
     if (self.localAVStream) {
         forAllTracksOnStream(self.localAVStream, function(t) {
@@ -988,15 +988,15 @@ let stopAllMedia = function(self) {
     }
 };
 
-let _tryPlayRemoteStream = function(self) {
+const _tryPlayRemoteStream = function(self) {
     if (self.getRemoteVideoElement() && self.remoteAVStream) {
-        let player = self.getRemoteVideoElement();
+        const player = self.getRemoteVideoElement();
         player.autoplay = true;
         self.assignElement(player,
                            self.URL.createObjectURL(self.remoteAVStream),
                            "remoteVideo");
         setTimeout(function() {
-            let vel = self.getRemoteVideoElement();
+            const vel = self.getRemoteVideoElement();
             if (vel.play) {
                 self.playElement(vel, "remoteVideo");
             }
@@ -1008,15 +1008,15 @@ let _tryPlayRemoteStream = function(self) {
     }
 };
 
-let _tryPlayRemoteAudioStream = function(self) {
+const _tryPlayRemoteAudioStream = function(self) {
     if (self.getRemoteAudioElement() && self.remoteAStream) {
-        let player = self.getRemoteAudioElement();
+        const player = self.getRemoteAudioElement();
         player.autoplay = true;
         self.assignElement(player,
                            self.URL.createObjectURL(self.remoteAStream),
                            "remoteAudio");
         setTimeout(function() {
-            let ael = self.getRemoteAudioElement();
+            const ael = self.getRemoteAudioElement();
             if (ael.play) {
                 self.playElement(ael, "remoteAudio");
             }
@@ -1028,7 +1028,7 @@ let _tryPlayRemoteAudioStream = function(self) {
     }
 };
 
-let checkForErrorListener = function(self) {
+const checkForErrorListener = function(self) {
     if (self.listeners("error").length === 0) {
         throw new Error(
             "You MUST attach an error listener using call.on('error', function() {})"
@@ -1036,27 +1036,27 @@ let checkForErrorListener = function(self) {
     }
 };
 
-let callError = function(code, msg) {
-    let e = new Error(msg);
+const callError = function(code, msg) {
+    const e = new Error(msg);
     e.code = code;
     return e;
 };
 
-let debuglog = function() {
+const debuglog = function() {
     if (DEBUG) {
         console.log(...arguments);
     }
 };
 
-let _sendCandidateQueue = function(self) {
+const _sendCandidateQueue = function(self) {
     if (self.candidateSendQueue.length === 0) {
         return;
     }
 
-    let cands = self.candidateSendQueue;
+    const cands = self.candidateSendQueue;
     self.candidateSendQueue = [];
     ++self.candidateSendTries;
-    let content = {
+    const content = {
         version: 0,
         call_id: self.callId,
         candidates: cands,
@@ -1079,7 +1079,7 @@ let _sendCandidateQueue = function(self) {
             return;
         }
 
-        let delayMs = 500 * Math.pow(2, self.candidateSendTries);
+        const delayMs = 500 * Math.pow(2, self.candidateSendTries);
         ++self.candidateSendTries;
         debuglog("Failed to send candidates. Retrying in " + delayMs + "ms");
         setTimeout(function() {
@@ -1088,7 +1088,7 @@ let _sendCandidateQueue = function(self) {
     });
 };
 
-let _placeCallWithConstraints = function(self, constraints) {
+const _placeCallWithConstraints = function(self, constraints) {
     self.client.callList[self.callId] = self;
     self.webRtc.getUserMedia(
         constraints,
@@ -1100,7 +1100,7 @@ let _placeCallWithConstraints = function(self, constraints) {
     self.config = constraints;
 };
 
-let _createPeerConnection = function(self) {
+const _createPeerConnection = function(self) {
     let servers = self.turnServers;
     if (self.webRtc.vendor === "mozilla") {
         // modify turnServers struct to match what mozilla expects.
@@ -1116,7 +1116,7 @@ let _createPeerConnection = function(self) {
         }
     }
 
-    let pc = new self.webRtc.RtcPeerConnection({
+    const pc = new self.webRtc.RtcPeerConnection({
         iceServers: servers,
     });
     pc.oniceconnectionstatechange = hookCallback(self, self._onIceConnectionStateChanged);
@@ -1126,8 +1126,8 @@ let _createPeerConnection = function(self) {
     return pc;
 };
 
-let _getChromeScreenSharingConstraints = function(call) {
-    let screen = global.screen;
+const _getChromeScreenSharingConstraints = function(call) {
+    const screen = global.screen;
     if (!screen) {
         call.emit("error", callError(
             MatrixCall.ERR_NO_USER_MEDIA,
@@ -1150,7 +1150,7 @@ let _getChromeScreenSharingConstraints = function(call) {
     };
 };
 
-let _getUserMediaVideoContraints = function(callType) {
+const _getUserMediaVideoContraints = function(callType) {
     switch (callType) {
         case 'voice':
             return ({audio: true, video: false});
@@ -1166,27 +1166,27 @@ let _getUserMediaVideoContraints = function(callType) {
     }
 };
 
-let hookCallback = function(call, fn) {
+const hookCallback = function(call, fn) {
     return function() {
         return fn.apply(call, arguments);
     };
 };
 
-let forAllVideoTracksOnStream = function(s, f) {
-    let tracks = s.getVideoTracks();
+const forAllVideoTracksOnStream = function(s, f) {
+    const tracks = s.getVideoTracks();
     for (let i = 0; i < tracks.length; i++) {
         f(tracks[i]);
     }
 };
 
-let forAllAudioTracksOnStream = function(s, f) {
-    let tracks = s.getAudioTracks();
+const forAllAudioTracksOnStream = function(s, f) {
+    const tracks = s.getAudioTracks();
     for (let i = 0; i < tracks.length; i++) {
         f(tracks[i]);
     }
 };
 
-let forAllTracksOnStream = function(s, f) {
+const forAllTracksOnStream = function(s, f) {
     forAllVideoTracksOnStream(s, f);
     forAllAudioTracksOnStream(s, f);
 };
@@ -1202,14 +1202,14 @@ module.exports.MatrixCall = MatrixCall;
  * @return {MatrixCall} the call or null if the browser doesn't support calling.
  */
 module.exports.createNewMatrixCall = function(client, roomId) {
-    let w = global.window;
-    let doc = global.document;
+    const w = global.window;
+    const doc = global.document;
     if (!w || !doc) {
         return null;
     }
-    let webRtc = {};
+    const webRtc = {};
     webRtc.isOpenWebRTC = function() {
-        let scripts = doc.getElementById("script");
+        const scripts = doc.getElementById("script");
         if (!scripts || !scripts.length) {
             return false;
         }
@@ -1220,7 +1220,7 @@ module.exports.createNewMatrixCall = function(client, roomId) {
         }
         return false;
     };
-    let getUserMedia = (
+    const getUserMedia = (
         w.navigator.getUserMedia || w.navigator.webkitGetUserMedia ||
         w.navigator.mozGetUserMedia
     );
@@ -1251,7 +1251,7 @@ module.exports.createNewMatrixCall = function(client, roomId) {
             !webRtc.RtcPeerConnection || !webRtc.getUserMedia) {
         return null; // WebRTC is not supported.
     }
-    let opts = {
+    const opts = {
         webRtc: webRtc,
         client: client,
         URL: w.URL,