diff --git a/.eslintrc.js b/.eslintrc.js
index 918ae4365..3059df17f 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -85,5 +85,14 @@ module.exports = {
             // We use a `logger` intermediary module
             "no-console": "error",
         },
+    }, {
+        files: [
+            "spec/**/*.ts",
+        ],
+        rules: {
+            // We don't need super strict typing in test utilities
+            "@typescript-eslint/explicit-function-return-type": "off",
+            "@typescript-eslint/explicit-member-accessibility": "off",
+        },
     }],
 };
diff --git a/package.json b/package.json
index fa89996e6..46a062cc8 100644
--- a/package.json
+++ b/package.json
@@ -99,7 +99,7 @@
     "eslint-config-google": "^0.14.0",
     "eslint-import-resolver-typescript": "^3.5.1",
     "eslint-plugin-import": "^2.26.0",
-    "eslint-plugin-matrix-org": "^0.7.0",
+    "eslint-plugin-matrix-org": "^0.8.0",
     "eslint-plugin-unicorn": "^44.0.2",
     "exorcist": "^2.0.0",
     "fake-indexeddb": "^4.0.0",
diff --git a/spec/integ/matrix-client-syncing.spec.ts b/spec/integ/matrix-client-syncing.spec.ts
index 216fbdbb1..8c3969bee 100644
--- a/spec/integ/matrix-client-syncing.spec.ts
+++ b/spec/integ/matrix-client-syncing.spec.ts
@@ -709,11 +709,11 @@ describe("MatrixClient syncing", () => {
                 const room = client!.getRoom(roomOne)!;
                 const stateAtStart = room.getLiveTimeline().getState(EventTimeline.BACKWARDS)!;
                 const startRoomNameEvent = stateAtStart.getStateEvents('m.room.name', '');
-                expect(startRoomNameEvent.getContent().name).toEqual('Old room name');
+                expect(startRoomNameEvent!.getContent().name).toEqual('Old room name');
 
                 const stateAtEnd = room.getLiveTimeline().getState(EventTimeline.FORWARDS)!;
                 const endRoomNameEvent = stateAtEnd.getStateEvents('m.room.name', '');
-                expect(endRoomNameEvent.getContent().name).toEqual('A new room name');
+                expect(endRoomNameEvent!.getContent().name).toEqual('A new room name');
             });
         });
 
@@ -1599,7 +1599,7 @@ describe("MatrixClient syncing", () => {
             expect(room.roomId).toBe(roomOne);
             expect(room.getMyMembership()).toBe("leave");
             expect(room.name).toBe("Room Name");
-            expect(room.currentState.getStateEvents("m.room.name", "").getId()).toBe("$eventId");
+            expect(room.currentState.getStateEvents("m.room.name", "")?.getId()).toBe("$eventId");
             expect(room.timeline[0].getContent().body).toBe("Message 1");
             expect(room.timeline[1].getContent().body).toBe("Message 2");
             client?.stopPeeking();
diff --git a/spec/unit/embedded.spec.ts b/spec/unit/embedded.spec.ts
index 436909be7..3e0ead871 100644
--- a/spec/unit/embedded.spec.ts
+++ b/spec/unit/embedded.spec.ts
@@ -179,7 +179,7 @@ describe("RoomWidgetClient", () => {
             // It should've also inserted the event into the room object
             const room = client.getRoom("!1:example.org");
             expect(room).not.toBeNull();
-            expect(room!.currentState.getStateEvents("org.example.foo", "bar").getEffectiveEvent()).toEqual(event);
+            expect(room!.currentState.getStateEvents("org.example.foo", "bar")?.getEffectiveEvent()).toEqual(event);
         });
 
         it("backfills", async () => {
@@ -195,7 +195,7 @@ describe("RoomWidgetClient", () => {
 
             const room = client.getRoom("!1:example.org");
             expect(room).not.toBeNull();
-            expect(room!.currentState.getStateEvents("org.example.foo", "bar").getEffectiveEvent()).toEqual(event);
+            expect(room!.currentState.getStateEvents("org.example.foo", "bar")?.getEffectiveEvent()).toEqual(event);
         });
     });
 
diff --git a/spec/unit/room-state.spec.ts b/spec/unit/room-state.spec.ts
index 5ee44f611..1ac3721a1 100644
--- a/spec/unit/room-state.spec.ts
+++ b/spec/unit/room-state.spec.ts
@@ -152,7 +152,7 @@ describe("RoomState", function() {
         it("should return a single MatrixEvent if a state_key was specified",
             function() {
                 const event = state.getStateEvents("m.room.member", userA);
-                expect(event.getContent()).toMatchObject({
+                expect(event?.getContent()).toMatchObject({
                     membership: "join",
                 });
             });
diff --git a/src/ReEmitter.ts b/src/ReEmitter.ts
index 6822e3d1e..2fa6eface 100644
--- a/src/ReEmitter.ts
+++ b/src/ReEmitter.ts
@@ -22,7 +22,7 @@ import { EventEmitter } from "events";
 import { ListenerMap, TypedEventEmitter } from "./models/typed-event-emitter";
 
 export class ReEmitter {
-    constructor(private readonly target: EventEmitter) {}
+    public constructor(private readonly target: EventEmitter) {}
 
     // Map from emitter to event name to re-emitter
     private reEmitters = new Map<EventEmitter, Map<string, (...args: any[]) => void>>();
@@ -38,7 +38,7 @@ export class ReEmitter {
             // We include the source as the last argument for event handlers which may need it,
             // such as read receipt listeners on the client class which won't have the context
             // of the room.
-            const forSource = (...args: any[]) => {
+            const forSource = (...args: any[]): void => {
                 // EventEmitter special cases 'error' to make the emit function throw if no
                 // handler is attached, which sort of makes sense for making sure that something
                 // handles an error, but for re-emitting, there could be a listener on the original
@@ -74,7 +74,7 @@ export class TypedReEmitter<
     Events extends string,
     Arguments extends ListenerMap<Events>,
 > extends ReEmitter {
-    constructor(target: TypedEventEmitter<Events, Arguments>) {
+    public constructor(target: TypedEventEmitter<Events, Arguments>) {
         super(target);
     }
 
diff --git a/src/ToDeviceMessageQueue.ts b/src/ToDeviceMessageQueue.ts
index 815927679..0b5b1786a 100644
--- a/src/ToDeviceMessageQueue.ts
+++ b/src/ToDeviceMessageQueue.ts
@@ -31,7 +31,7 @@ export class ToDeviceMessageQueue {
     private retryTimeout: ReturnType<typeof setTimeout> | null = null;
     private retryAttempts = 0;
 
-    constructor(private client: MatrixClient) {
+    public constructor(private client: MatrixClient) {
     }
 
     public start(): void {
diff --git a/src/client.ts b/src/client.ts
index a3b44dfa0..c38160c53 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -1010,7 +1010,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     // A manager for determining which invites should be ignored.
     public readonly ignoredInvites: IgnoredInvites;
 
-    constructor(opts: IMatrixClientCreateOpts) {
+    public constructor(opts: IMatrixClientCreateOpts) {
         super();
 
         opts.baseUrl = utils.ensureNoTrailingSlash(opts.baseUrl);
@@ -1232,7 +1232,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         // shallow-copy the opts dict before modifying and storing it
         this.clientOpts = Object.assign({}, opts) as IStoredClientOpts;
         this.clientOpts.crypto = this.crypto;
-        this.clientOpts.canResetEntireTimeline = (roomId) => {
+        this.clientOpts.canResetEntireTimeline = (roomId): boolean => {
             if (!this.canResetTimelineCallback) {
                 return false;
             }
@@ -1259,7 +1259,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * High level helper method to stop the client from polling and allow a
      * clean shutdown.
      */
-    public stopClient() {
+    public stopClient(): void {
         this.crypto?.stop(); // crypto might have been initialised even if the client wasn't fully started
 
         if (!this.clientRunning) return; // already stopped
@@ -1536,7 +1536,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * when creating the client.
      * @param {boolean} force True to force use of TURN servers
      */
-    public setForceTURN(force: boolean) {
+    public setForceTURN(force: boolean): void {
         this.forceTURN = force;
     }
 
@@ -1544,7 +1544,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * Set whether to advertise transfer support to other parties on Matrix calls.
      * @param {boolean} support True to advertise the 'm.call.transferee' capability
      */
-    public setSupportsCallTransfer(support: boolean) {
+    public setSupportsCallTransfer(support: boolean): void {
         this.supportsCallTransfer = support;
     }
 
@@ -1678,7 +1678,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * and may change without warning.</b>
      * @param {boolean} guest True if this is a guest account.
      */
-    public setGuest(guest: boolean) {
+    public setGuest(guest: boolean): void {
         // EXPERIMENTAL:
         // If the token is a macaroon, it should be encoded in it that it is a 'guest'
         // access token, which means that the SDK can determine this entirely without
@@ -1721,7 +1721,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * @param {EventTimelineSet} set
      */
-    public setNotifTimelineSet(set: EventTimelineSet) {
+    public setNotifTimelineSet(set: EventTimelineSet): void {
         this.notifTimelineSet = set;
     }
 
@@ -2279,11 +2279,11 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * send, in order to speed up sending of the message.
      * @param {module:models/room} room the room the event is in
      */
-    public prepareToEncrypt(room: Room) {
+    public prepareToEncrypt(room: Room): void {
         if (!this.crypto) {
             throw new Error("End-to-end encryption disabled");
         }
-        return this.crypto.prepareToEncrypt(room);
+        this.crypto.prepareToEncrypt(room);
     }
 
     /**
@@ -2324,7 +2324,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *     auth data as an object. Can be called multiple times, first with an empty
      *     authDict, to obtain the flows.
      */
-    public bootstrapCrossSigning(opts: IBootstrapCrossSigningOpts) {
+    public bootstrapCrossSigning(opts: IBootstrapCrossSigningOpts): Promise<void> {
         if (!this.crypto) {
             throw new Error("End-to-end encryption disabled");
         }
@@ -2352,11 +2352,11 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * @param {boolean} val True to trust cross-signed devices
      */
-    public setCryptoTrustCrossSignedDevices(val: boolean) {
+    public setCryptoTrustCrossSignedDevices(val: boolean): void {
         if (!this.crypto) {
             throw new Error("End-to-end encryption disabled");
         }
-        return this.crypto.setCryptoTrustCrossSignedDevices(val);
+        this.crypto.setCryptoTrustCrossSignedDevices(val);
     }
 
     /**
@@ -2497,7 +2497,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * @param {Array} keys The IDs of the keys to use to encrypt the secret or null/undefined
      *     to use the default (will throw if no default key is set).
      */
-    public storeSecret(name: string, secret: string, keys?: string[]) {
+    public storeSecret(name: string, secret: string, keys?: string[]): Promise<void> {
         if (!this.crypto) {
             throw new Error("End-to-end encryption disabled");
         }
@@ -2575,7 +2575,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * @param {string} keyId The new default key ID
      */
-    public setDefaultSecretStorageKeyId(keyId: string) {
+    public setDefaultSecretStorageKeyId(keyId: string): Promise<void> {
         if (!this.crypto) {
             throw new Error("End-to-end encryption disabled");
         }
@@ -2716,7 +2716,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * This should not normally be necessary.
      */
-    public forceDiscardSession(roomId: string) {
+    public forceDiscardSession(roomId: string): void {
         if (!this.crypto) {
             throw new Error("End-to-End encryption disabled");
         }
@@ -2840,7 +2840,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     /**
      * Disable backing up of keys.
      */
-    public disableKeyBackup() {
+    public disableKeyBackup(): void {
         if (!this.crypto) {
             throw new Error("End-to-end encryption disabled");
         }
@@ -3044,7 +3044,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * Marks all group sessions as needing to be backed up and schedules them to
      * upload in the background as soon as possible.
      */
-    public async scheduleAllGroupSessionsForBackup() {
+    public async scheduleAllGroupSessionsForBackup(): Promise<void> {
         if (!this.crypto) {
             throw new Error("End-to-end encryption disabled");
         }
@@ -3401,7 +3401,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * @param {array} userIds a list of users to share with.  The keys will be sent to
      *     all of the user's current devices.
      */
-    public async sendSharedHistoryKeys(roomId: string, userIds: string[]) {
+    public async sendSharedHistoryKeys(roomId: string, userIds: string[]): Promise<void> {
         if (!this.crypto) {
             throw new Error("End-to-end encryption disabled");
         }
@@ -3685,7 +3685,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * @param {MatrixEvent} event   Event to cancel
      * @throws Error if the event is not in QUEUED, NOT_SENT or ENCRYPTING state
      */
-    public cancelPendingEvent(event: MatrixEvent) {
+    public cancelPendingEvent(event: MatrixEvent): void {
         if (![EventStatus.QUEUED, EventStatus.NOT_SENT, EventStatus.ENCRYPTING].includes(event.status!)) {
             throw new Error("cannot cancel an event with status " + event.status);
         }
@@ -3834,7 +3834,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     public async unstable_createLiveBeacon(
         roomId: Room["roomId"],
         beaconInfoContent: MBeaconInfoEventContent,
-    ) {
+    ): Promise<ISendEventResponse> {
         return this.unstable_setLiveBeacon(roomId, beaconInfoContent);
     }
 
@@ -3849,7 +3849,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     public async unstable_setLiveBeacon(
         roomId: string,
         beaconInfoContent: MBeaconInfoEventContent,
-    ) {
+    ): Promise<ISendEventResponse> {
         return this.sendStateEvent(roomId, M_BEACON_INFO.name, beaconInfoContent, this.getUserId()!);
     }
 
@@ -4121,7 +4121,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         return this.isRoomEncrypted(roomId) ? EventType.RoomMessageEncrypted : eventType;
     }
 
-    protected updatePendingEventStatus(room: Room | null, event: MatrixEvent, newStatus: EventStatus) {
+    protected updatePendingEventStatus(room: Room | null, event: MatrixEvent, newStatus: EventStatus): void {
         if (room) {
             room.updatePendingEvent(event, newStatus);
         } else {
@@ -4944,12 +4944,12 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         const populationResults: { [roomId: string]: Error } = {};
         const promises: Promise<any>[] = [];
 
-        const doLeave = (roomId: string) => {
+        const doLeave = (roomId: string): Promise<void> => {
             return this.leave(roomId).then(() => {
                 delete populationResults[roomId];
             }).catch((err) => {
+                // suppress error
                 populationResults[roomId] = err;
-                return null; // suppress error
             });
         };
 
@@ -5904,7 +5904,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * Reset the notifTimelineSet entirely, paginating in some historical notifs as
      * a starting point for subsequent pagination.
      */
-    public resetNotifTimelineSet() {
+    public resetNotifTimelineSet(): void {
         if (!this.notifTimelineSet) {
             return;
         }
@@ -5949,7 +5949,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     /**
      * Stop any ongoing room peeking.
      */
-    public stopPeeking() {
+    public stopPeeking(): void {
         if (this.peekSync) {
             this.peekSync.stopPeeking();
             this.peekSync = null;
@@ -6683,7 +6683,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * @param {boolean} allow
      */
-    public setFallbackICEServerAllowed(allow: boolean) {
+    public setFallbackICEServerAllowed(allow: boolean): void {
         this.fallbackICEServerAllowed = allow;
     }
 
@@ -7024,7 +7024,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * Default: returns false.
      * @param {Function} cb The callback which will be invoked.
      */
-    public setCanResetTimelineCallback(cb: ResetTimelineCallback) {
+    public setCanResetTimelineCallback(cb: ResetTimelineCallback): void {
         this.canResetTimelineCallback = cb;
     }
 
@@ -7164,7 +7164,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * Set the identity server URL of this client
      * @param {string} url New identity server URL
      */
-    public setIdentityServerUrl(url: string) {
+    public setIdentityServerUrl(url: string): void {
         this.idBaseUrl = utils.ensureNoTrailingSlash(url);
         this.http.setIdBaseUrl(this.idBaseUrl);
     }
@@ -7181,7 +7181,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * Set the access token associated with this account.
      * @param {string} token The new access token.
      */
-    public setAccessToken(token: string) {
+    public setAccessToken(token: string): void {
         this.http.opts.accessToken = token;
     }
 
diff --git a/src/content-helpers.ts b/src/content-helpers.ts
index 4dbb37b21..6fa4b684b 100644
--- a/src/content-helpers.ts
+++ b/src/content-helpers.ts
@@ -33,6 +33,7 @@ import {
     LegacyLocationEventContent,
 } from "./@types/location";
 import { MRoomTopicEventContent, MTopicContent, M_TOPIC } from "./@types/topic";
+import { IContent } from "./models/event";
 
 /**
  * Generates the content for a HTML Message event
@@ -40,7 +41,7 @@ import { MRoomTopicEventContent, MTopicContent, M_TOPIC } from "./@types/topic";
  * @param {string} htmlBody the HTML representation of the message
  * @returns {{msgtype: string, format: string, body: string, formatted_body: string}}
  */
-export function makeHtmlMessage(body: string, htmlBody: string) {
+export function makeHtmlMessage(body: string, htmlBody: string): IContent {
     return {
         msgtype: MsgType.Text,
         format: "org.matrix.custom.html",
@@ -55,7 +56,7 @@ export function makeHtmlMessage(body: string, htmlBody: string) {
  * @param {string} htmlBody the HTML representation of the notice
  * @returns {{msgtype: string, format: string, body: string, formatted_body: string}}
  */
-export function makeHtmlNotice(body: string, htmlBody: string) {
+export function makeHtmlNotice(body: string, htmlBody: string): IContent {
     return {
         msgtype: MsgType.Notice,
         format: "org.matrix.custom.html",
@@ -70,7 +71,7 @@ export function makeHtmlNotice(body: string, htmlBody: string) {
  * @param {string} htmlBody the HTML representation of the emote
  * @returns {{msgtype: string, format: string, body: string, formatted_body: string}}
  */
-export function makeHtmlEmote(body: string, htmlBody: string) {
+export function makeHtmlEmote(body: string, htmlBody: string): IContent {
     return {
         msgtype: MsgType.Emote,
         format: "org.matrix.custom.html",
@@ -84,7 +85,7 @@ export function makeHtmlEmote(body: string, htmlBody: string) {
  * @param {string} body the plaintext body of the emote
  * @returns {{msgtype: string, body: string}}
  */
-export function makeTextMessage(body: string) {
+export function makeTextMessage(body: string): IContent {
     return {
         msgtype: MsgType.Text,
         body: body,
@@ -96,7 +97,7 @@ export function makeTextMessage(body: string) {
  * @param {string} body the plaintext body of the notice
  * @returns {{msgtype: string, body: string}}
  */
-export function makeNotice(body: string) {
+export function makeNotice(body: string): IContent {
     return {
         msgtype: MsgType.Notice,
         body: body,
@@ -108,7 +109,7 @@ export function makeNotice(body: string) {
  * @param {string} body the plaintext body of the emote
  * @returns {{msgtype: string, body: string}}
  */
-export function makeEmoteMessage(body: string) {
+export function makeEmoteMessage(body: string): IContent {
     return {
         msgtype: MsgType.Emote,
         body: body,
diff --git a/src/crypto/CrossSigning.ts b/src/crypto/CrossSigning.ts
index 59907bdbf..e776b93ad 100644
--- a/src/crypto/CrossSigning.ts
+++ b/src/crypto/CrossSigning.ts
@@ -21,7 +21,7 @@ limitations under the License.
 
 import { PkSigning } from "@matrix-org/olm";
 
-import { decodeBase64, encodeBase64, pkSign, pkVerify } from './olmlib';
+import { decodeBase64, encodeBase64, IObject, pkSign, pkVerify } from './olmlib';
 import { logger } from '../logger';
 import { IndexedDBCryptoStore } from '../crypto/store/indexeddb-crypto-store';
 import { decryptAES, encryptAES } from './aes';
@@ -74,7 +74,7 @@ export class CrossSigningInfo {
      *     Requires getCrossSigningKey and saveCrossSigningKeys
      * @param {object} cacheCallbacks Callbacks used to interact with the cache
      */
-    constructor(
+    public constructor(
         public readonly userId: string,
         private callbacks: ICryptoCallbacks = {},
         private cacheCallbacks: ICacheCallbacks = {},
@@ -175,7 +175,7 @@ export class CrossSigningInfo {
         // check what SSSS keys have encrypted the master key (if any)
         const stored = await secretStorage.isStored("m.cross_signing.master") || {};
         // then check which of those SSSS keys have also encrypted the SSK and USK
-        function intersect(s: Record<string, ISecretStorageKeyInfo>) {
+        function intersect(s: Record<string, ISecretStorageKeyInfo>): void {
             for (const k of Object.keys(stored)) {
                 if (!s[k]) {
                     delete stored[k];
@@ -586,7 +586,14 @@ export class CrossSigningInfo {
     }
 }
 
-function deviceToObject(device: DeviceInfo, userId: string) {
+interface DeviceObject extends IObject {
+    algorithms: string[];
+    keys: Record<string, string>;
+    device_id: string;
+    user_id: string;
+}
+
+function deviceToObject(device: DeviceInfo, userId: string): DeviceObject {
     return {
         algorithms: device.algorithms,
         keys: device.keys,
@@ -606,7 +613,7 @@ export enum CrossSigningLevel {
  * Represents the ways in which we trust a user
  */
 export class UserTrustLevel {
-    constructor(
+    public constructor(
         private readonly crossSigningVerified: boolean,
         private readonly crossSigningVerifiedBefore: boolean,
         private readonly tofu: boolean,
@@ -646,7 +653,7 @@ export class UserTrustLevel {
  * Represents the ways in which we trust a device
  */
 export class DeviceTrustLevel {
-    constructor(
+    public constructor(
         public readonly crossSigningVerified: boolean,
         public readonly tofu: boolean,
         private readonly localVerified: boolean,
@@ -775,7 +782,7 @@ export async function requestKeysDuringVerification(
         // CrossSigningInfo.getCrossSigningKey() to validate/cache
         const crossSigning = new CrossSigningInfo(
             original.userId,
-            { getCrossSigningKey: async (type) => {
+            { getCrossSigningKey: async (type): Promise<Uint8Array> => {
                 logger.debug("Cross-signing: requesting secret", type, deviceId);
                 const { promise } = client.requestSecret(
                     `m.cross_signing.${type}`, [deviceId],
@@ -801,7 +808,7 @@ export async function requestKeysDuringVerification(
         });
 
         // also request and cache the key backup key
-        const backupKeyPromise = (async () => {
+        const backupKeyPromise = (async (): Promise<void> => {
             const cachedKey = await client.crypto!.getSessionBackupPrivateKey();
             if (!cachedKey) {
                 logger.info("No cached backup key found. Requesting...");
diff --git a/src/crypto/DeviceList.ts b/src/crypto/DeviceList.ts
index c4345437c..da40a03f2 100644
--- a/src/crypto/DeviceList.ts
+++ b/src/crypto/DeviceList.ts
@@ -102,7 +102,7 @@ export class DeviceList extends TypedEventEmitter<EmittedEvents, CryptoEventHand
 
     private readonly serialiser: DeviceListUpdateSerialiser;
 
-    constructor(
+    public constructor(
         baseApis: MatrixClient,
         private readonly cryptoStore: CryptoStore,
         olmDevice: OlmDevice,
@@ -117,7 +117,7 @@ export class DeviceList extends TypedEventEmitter<EmittedEvents, CryptoEventHand
     /**
      * Load the device tracking state from storage
      */
-    public async load() {
+    public async load(): Promise<void> {
         await this.cryptoStore.doTxn(
             'readonly', [IndexedDBCryptoStore.STORE_DEVICE_DATA], (txn) => {
                 this.cryptoStore.getEndToEndDeviceData(txn, (deviceData) => {
@@ -150,7 +150,7 @@ export class DeviceList extends TypedEventEmitter<EmittedEvents, CryptoEventHand
         }
     }
 
-    public stop() {
+    public stop(): void {
         if (this.saveTimer !== null) {
             clearTimeout(this.saveTimer);
         }
@@ -693,7 +693,7 @@ class DeviceListUpdateSerialiser {
      * @param {object} olmDevice The Olm Device
      * @param {object} deviceList The device list object, the device list to be updated
      */
-    constructor(
+    public constructor(
         private readonly baseApis: MatrixClient,
         private readonly olmDevice: OlmDevice,
         private readonly deviceList: DeviceList,
diff --git a/src/crypto/EncryptionSetup.ts b/src/crypto/EncryptionSetup.ts
index e6ad10f39..253c83c1d 100644
--- a/src/crypto/EncryptionSetup.ts
+++ b/src/crypto/EncryptionSetup.ts
@@ -61,7 +61,7 @@ export class EncryptionSetupBuilder {
      * @param {Object.<String, MatrixEvent>} accountData pre-existing account data, will only be read, not written.
      * @param {CryptoCallbacks} delegateCryptoCallbacks crypto callbacks to delegate to if the key isn't in cache yet
      */
-    constructor(accountData: Record<string, MatrixEvent>, delegateCryptoCallbacks?: ICryptoCallbacks) {
+    public constructor(accountData: Record<string, MatrixEvent>, delegateCryptoCallbacks?: ICryptoCallbacks) {
         this.accountDataClientAdapter = new AccountDataClientAdapter(accountData);
         this.crossSigningCallbacks = new CrossSigningCallbacks();
         this.ssssCryptoCallbacks = new SSSSCryptoCallbacks(delegateCryptoCallbacks);
@@ -192,7 +192,7 @@ export class EncryptionSetupOperation {
      * @param  {Object} keyBackupInfo
      * @param  {Object} keySignatures
      */
-    constructor(
+    public constructor(
         private readonly accountData: Map<string, object>,
         private readonly crossSigningKeys?: ICrossSigningKeys,
         private readonly keyBackupInfo?: IKeyBackupInfo,
@@ -272,7 +272,7 @@ class AccountDataClientAdapter
     /**
      * @param  {Object.<String, MatrixEvent>} existingValues existing account data
      */
-    constructor(private readonly existingValues: Record<string, MatrixEvent>) {
+    public constructor(private readonly existingValues: Record<string, MatrixEvent>) {
         super();
     }
 
@@ -342,7 +342,7 @@ class CrossSigningCallbacks implements ICryptoCallbacks, ICacheCallbacks {
         return Promise.resolve(this.privateKeys.get(type) ?? null);
     }
 
-    public saveCrossSigningKeys(privateKeys: Record<string, Uint8Array>) {
+    public saveCrossSigningKeys(privateKeys: Record<string, Uint8Array>): void {
         for (const [type, privateKey] of Object.entries(privateKeys)) {
             this.privateKeys.set(type, privateKey);
         }
@@ -356,7 +356,7 @@ class CrossSigningCallbacks implements ICryptoCallbacks, ICacheCallbacks {
 class SSSSCryptoCallbacks {
     private readonly privateKeys = new Map<string, Uint8Array>();
 
-    constructor(private readonly delegateCryptoCallbacks?: ICryptoCallbacks) {}
+    public constructor(private readonly delegateCryptoCallbacks?: ICryptoCallbacks) {}
 
     public async getSecretStorageKey(
         { keys }: { keys: Record<string, ISecretStorageKeyInfo> },
diff --git a/src/crypto/OlmDevice.ts b/src/crypto/OlmDevice.ts
index 84eec463c..efa34ad41 100644
--- a/src/crypto/OlmDevice.ts
+++ b/src/crypto/OlmDevice.ts
@@ -177,13 +177,13 @@ export class OlmDevice {
     // Used by olm to serialise prekey message decryptions
     public olmPrekeyPromise: Promise<any> = Promise.resolve(); // set by consumers
 
-    constructor(private readonly cryptoStore: CryptoStore) {
+    public constructor(private readonly cryptoStore: CryptoStore) {
     }
 
     /**
      * @return {array} The version of Olm.
      */
-    static getOlmVersion(): [number, number, number] {
+    public static getOlmVersion(): [number, number, number] {
         return global.Olm.get_library_version();
     }
 
@@ -1515,7 +1515,9 @@ export class OlmDevice {
         });
     }
 
-    async getSharedHistoryInboundGroupSessions(roomId: string): Promise<[senderKey: string, sessionId: string][]> {
+    public async getSharedHistoryInboundGroupSessions(
+        roomId: string,
+    ): Promise<[senderKey: string, sessionId: string][]> {
         let result: Promise<[senderKey: string, sessionId: string][]>;
         await this.cryptoStore.doTxn(
             'readonly', [
diff --git a/src/crypto/OutgoingRoomKeyRequestManager.ts b/src/crypto/OutgoingRoomKeyRequestManager.ts
index d5d1c3003..427234347 100644
--- a/src/crypto/OutgoingRoomKeyRequestManager.ts
+++ b/src/crypto/OutgoingRoomKeyRequestManager.ts
@@ -102,7 +102,7 @@ export class OutgoingRoomKeyRequestManager {
 
     private clientRunning = true;
 
-    constructor(
+    public constructor(
         private readonly baseApis: MatrixClient,
         private readonly deviceId: string,
         private readonly cryptoStore: CryptoStore,
@@ -352,7 +352,7 @@ export class OutgoingRoomKeyRequestManager {
             return;
         }
 
-        const startSendingOutgoingRoomKeyRequests = () => {
+        const startSendingOutgoingRoomKeyRequests = (): void => {
             if (this.sendOutgoingRoomKeyRequestsRunning) {
                 throw new Error("RoomKeyRequestSend already in progress!");
             }
diff --git a/src/crypto/RoomList.ts b/src/crypto/RoomList.ts
index f0e09b657..672ef473c 100644
--- a/src/crypto/RoomList.ts
+++ b/src/crypto/RoomList.ts
@@ -38,7 +38,7 @@ export class RoomList {
     // Object of roomId -> room e2e info object (body of the m.room.encryption event)
     private roomEncryption: Record<string, IRoomEncryption> = {};
 
-    constructor(private readonly cryptoStore?: CryptoStore) {}
+    public constructor(private readonly cryptoStore?: CryptoStore) {}
 
     public async init(): Promise<void> {
         await this.cryptoStore!.doTxn(
diff --git a/src/crypto/SecretStorage.ts b/src/crypto/SecretStorage.ts
index d1d6285fc..5c13ba4b0 100644
--- a/src/crypto/SecretStorage.ts
+++ b/src/crypto/SecretStorage.ts
@@ -78,7 +78,7 @@ export class SecretStorage<B extends MatrixClient | undefined = MatrixClient> {
     // as you don't request any secrets.
     // A better solution would probably be to split this class up into secret storage and
     // secret sharing which are really two separate things, even though they share an MSC.
-    constructor(
+    public constructor(
         private readonly accountDataAdapter: IAccountDataClient,
         private readonly cryptoCallbacks: ICryptoCallbacks,
         private readonly baseApis: B,
@@ -381,7 +381,7 @@ export class SecretStorage<B extends MatrixClient | undefined = MatrixClient> {
         const deferred = defer<string>();
         this.requests.set(requestId, { name, devices, deferred });
 
-        const cancel = (reason: string) => {
+        const cancel = (reason: string): void => {
             // send cancellation event
             const cancelData = {
                 action: "request_cancellation",
diff --git a/src/crypto/algorithms/base.ts b/src/crypto/algorithms/base.ts
index 190bfa437..d6c70bc10 100644
--- a/src/crypto/algorithms/base.ts
+++ b/src/crypto/algorithms/base.ts
@@ -78,7 +78,7 @@ export abstract class EncryptionAlgorithm {
     protected readonly baseApis: MatrixClient;
     protected readonly roomId?: string;
 
-    constructor(params: IParams) {
+    public constructor(params: IParams) {
         this.userId = params.userId;
         this.deviceId = params.deviceId;
         this.crypto = params.crypto;
@@ -150,7 +150,7 @@ export abstract class DecryptionAlgorithm {
     protected readonly baseApis: MatrixClient;
     protected readonly roomId?: string;
 
-    constructor(params: DecryptionClassParams) {
+    public constructor(params: DecryptionClassParams) {
         this.userId = params.userId;
         this.crypto = params.crypto;
         this.olmDevice = params.olmDevice;
@@ -242,7 +242,7 @@ export abstract class DecryptionAlgorithm {
 export class DecryptionError extends Error {
     public readonly detailedString: string;
 
-    constructor(public readonly code: string, msg: string, details?: Record<string, string | Error>) {
+    public constructor(public readonly code: string, msg: string, details?: Record<string, string | Error>) {
         super(msg);
         this.code = code;
         this.name = 'DecryptionError';
@@ -272,7 +272,7 @@ function detailedStringForDecryptionError(err: DecryptionError, details?: Record
  * @extends Error
  */
 export class UnknownDeviceError extends Error {
-    constructor(
+    public constructor(
         msg: string,
         public readonly devices: Record<string, Record<string, object>>,
         public event?: MatrixEvent,
diff --git a/src/crypto/algorithms/megolm.ts b/src/crypto/algorithms/megolm.ts
index dd53bfa05..cbad327a6 100644
--- a/src/crypto/algorithms/megolm.ts
+++ b/src/crypto/algorithms/megolm.ts
@@ -136,7 +136,7 @@ class OutboundSessionInfo {
     public sharedWithDevices: Record<string, Record<string, SharedWithData>> = {};
     public blockedDevicesNotified: Record<string, Record<string, boolean>> = {};
 
-    constructor(public readonly sessionId: string, public readonly sharedHistory = false) {
+    public constructor(public readonly sessionId: string, public readonly sharedHistory = false) {
         this.creationTime = new Date().getTime();
     }
 
@@ -248,7 +248,7 @@ class MegolmEncryption extends EncryptionAlgorithm {
 
     protected readonly roomId: string;
 
-    constructor(params: IParams & Required<Pick<IParams, "roomId">>) {
+    public constructor(params: IParams & Required<Pick<IParams, "roomId">>) {
         super(params);
         this.roomId = params.roomId;
 
@@ -347,7 +347,7 @@ class MegolmEncryption extends EncryptionAlgorithm {
         singleOlmCreationPhase: boolean,
         blocked: IBlockedMap,
         session: OutboundSessionInfo,
-    ) {
+    ): Promise<void> {
         // now check if we need to share with any devices
         const shareMap: Record<string, DeviceInfo[]> = {};
 
@@ -386,13 +386,13 @@ class MegolmEncryption extends EncryptionAlgorithm {
         );
 
         await Promise.all([
-            (async () => {
+            (async (): Promise<void> => {
                 // share keys with devices that we already have a session for
                 logger.debug(`Sharing keys with existing Olm sessions in ${this.roomId}`, olmSessions);
                 await this.shareKeyWithOlmSessions(session, key, payload, olmSessions);
                 logger.debug(`Shared keys with existing Olm sessions in ${this.roomId}`);
             })(),
-            (async () => {
+            (async (): Promise<void> => {
                 logger.debug(
                     `Sharing keys (start phase 1) with new Olm sessions in ${this.roomId}`,
                     devicesWithoutSession,
@@ -415,7 +415,7 @@ class MegolmEncryption extends EncryptionAlgorithm {
                 if (!singleOlmCreationPhase && (Date.now() - start < 10000)) {
                     // perform the second phase of olm session creation if requested,
                     // and if the first phase didn't take too long
-                    (async () => {
+                    (async (): Promise<void> => {
                         // Retry sending keys to devices that we were unable to establish
                         // an olm session for.  This time, we use a longer timeout, but we
                         // do this in the background and don't block anything else while we
@@ -452,7 +452,7 @@ class MegolmEncryption extends EncryptionAlgorithm {
                 }
                 logger.debug(`Shared keys (all phases done) with new Olm sessions in ${this.roomId}`);
             })(),
-            (async () => {
+            (async (): Promise<void> => {
                 logger.debug(`There are ${Object.entries(blocked).length} blocked devices in ${this.roomId}`,
                     Object.entries(blocked));
 
@@ -809,7 +809,7 @@ class MegolmEncryption extends EncryptionAlgorithm {
         errorDevices: IOlmDevice[],
         otkTimeout: number,
         failedServers?: string[],
-    ) {
+    ): Promise<void> {
         logger.debug(`Ensuring Olm sessions for devices in ${this.roomId}`);
         const devicemap = await olmlib.ensureOlmSessionsForDevices(
             this.olmDevice, this.baseApis, devicesByUser, false, otkTimeout, failedServers,
@@ -969,7 +969,7 @@ class MegolmEncryption extends EncryptionAlgorithm {
 
         this.encryptionPreparation = {
             startTime: Date.now(),
-            promise: (async () => {
+            promise: (async (): Promise<void> => {
                 try {
                     logger.debug(`Getting devices in ${this.roomId}`);
                     const [devicesInRoom, blocked] = await this.getDevicesInRoom(room);
@@ -1231,7 +1231,7 @@ class MegolmDecryption extends DecryptionAlgorithm {
 
     protected readonly roomId: string;
 
-    constructor(params: DecryptionClassParams<IParams & Required<Pick<IParams, "roomId">>>) {
+    public constructor(params: DecryptionClassParams<IParams & Required<Pick<IParams, "roomId">>>) {
         super(params);
         this.roomId = params.roomId;
     }
diff --git a/src/crypto/backup.ts b/src/crypto/backup.ts
index d9c1ba458..f2160165b 100644
--- a/src/crypto/backup.ts
+++ b/src/crypto/backup.ts
@@ -120,7 +120,7 @@ export class BackupManager {
     private sendingBackups: boolean; // Are we currently sending backups?
     private sessionLastCheckAttemptedTime: Record<string, number> = {}; // When did we last try to check the server for a given session id?
 
-    constructor(private readonly baseApis: MatrixClient, public readonly getKey: GetKey) {
+    public constructor(private readonly baseApis: MatrixClient, public readonly getKey: GetKey) {
         this.checkedForBackup = false;
         this.sendingBackups = false;
     }
@@ -609,7 +609,7 @@ export class BackupManager {
 export class Curve25519 implements BackupAlgorithm {
     public static algorithmName = "m.megolm_backup.v1.curve25519-aes-sha2";
 
-    constructor(
+    public constructor(
         public authData: ICurve25519AuthData,
         private publicKey: any, // FIXME: PkEncryption
         private getKey: () => Promise<Uint8Array>,
@@ -661,7 +661,7 @@ export class Curve25519 implements BackupAlgorithm {
         }
     }
 
-    public get untrusted() { return true; }
+    public get untrusted(): boolean { return true; }
 
     public async encryptSession(data: Record<string, any>): Promise<any> {
         const plainText: Record<string, any> = Object.assign({}, data);
@@ -735,7 +735,7 @@ const UNSTABLE_MSC3270_NAME = new UnstableValue(
 export class Aes256 implements BackupAlgorithm {
     public static algorithmName = UNSTABLE_MSC3270_NAME.name;
 
-    constructor(
+    public constructor(
         public readonly authData: IAes256AuthData,
         private readonly key: Uint8Array,
     ) {}
@@ -786,7 +786,7 @@ export class Aes256 implements BackupAlgorithm {
         }
     }
 
-    public get untrusted() { return false; }
+    public get untrusted(): boolean { return false; }
 
     public encryptSession(data: Record<string, any>): Promise<any> {
         const plainText: Record<string, any> = Object.assign({}, data);
diff --git a/src/crypto/dehydration.ts b/src/crypto/dehydration.ts
index 5b12159ae..cc6b252da 100644
--- a/src/crypto/dehydration.ts
+++ b/src/crypto/dehydration.ts
@@ -62,7 +62,7 @@ export class DehydrationManager {
     private keyInfo?: {[props: string]: any};
     private deviceDisplayName?: string;
 
-    constructor(private readonly crypto: Crypto) {
+    public constructor(private readonly crypto: Crypto) {
         this.getDehydrationKeyFromCache();
     }
 
@@ -294,7 +294,7 @@ export class DehydrationManager {
         }
     }
 
-    public stop() {
+    public stop(): void {
         if (this.timeoutId) {
             global.clearTimeout(this.timeoutId);
             this.timeoutId = undefined;
diff --git a/src/crypto/deviceinfo.ts b/src/crypto/deviceinfo.ts
index 00ebf7c38..3b4d53f68 100644
--- a/src/crypto/deviceinfo.ts
+++ b/src/crypto/deviceinfo.ts
@@ -94,7 +94,7 @@ export class DeviceInfo {
     public unsigned: Record<string, any> = {};
     public signatures: ISignatures = {};
 
-    constructor(public readonly deviceId: string) {}
+    public constructor(public readonly deviceId: string) {}
 
     /**
      * Prepare a DeviceInfo for JSON serialisation in the session store
diff --git a/src/crypto/index.ts b/src/crypto/index.ts
index 2a55d75fe..04a6e5e1a 100644
--- a/src/crypto/index.ts
+++ b/src/crypto/index.ts
@@ -278,7 +278,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     /**
      * @return {string} The version of Olm.
      */
-    static getOlmVersion(): [number, number, number] {
+    public static getOlmVersion(): [number, number, number] {
         return OlmDevice.getOlmVersion();
     }
 
@@ -372,7 +372,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
      *    Each element can either be a string from MatrixClient.verificationMethods
      *    or a class that implements a verification method.
      */
-    constructor(
+    public constructor(
         public readonly baseApis: MatrixClient,
         public readonly userId: string,
         private readonly deviceId: string,
@@ -465,7 +465,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
 
         // Assuming no app-supplied callback, default to getting from SSSS.
         if (!cryptoCallbacks.getCrossSigningKey && cryptoCallbacks.getSecretStorageKey) {
-            cryptoCallbacks.getCrossSigningKey = async (type) => {
+            cryptoCallbacks.getCrossSigningKey = async (type): Promise<Uint8Array | null> => {
                 return CrossSigningInfo.getFromSecretStorage(type, this.secretStorage);
             };
         }
@@ -709,7 +709,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         );
 
         // Reset the cross-signing keys
-        const resetCrossSigning = async () => {
+        const resetCrossSigning = async (): Promise<void> => {
             crossSigningInfo.resetKeys();
             // Sign master key with device key
             await this.signObject(crossSigningInfo.keys.master);
@@ -846,12 +846,12 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
      */
     // TODO this does not resolve with what it says it does
     public async bootstrapSecretStorage({
-        createSecretStorageKey = async () => ({} as IRecoveryKey),
+        createSecretStorageKey = async (): Promise<IRecoveryKey> => ({} as IRecoveryKey),
         keyBackupInfo,
         setupNewKeyBackup,
         setupNewSecretStorage,
         getKeyBackupPassphrase,
-    }: ICreateSecretStorageOpts = {}) {
+    }: ICreateSecretStorageOpts = {}): Promise<void> {
         logger.log("Bootstrapping Secure Secret Storage");
         const delegateCryptoCallbacks = this.baseApis.cryptoCallbacks;
         const builder = new EncryptionSetupBuilder(
@@ -868,7 +868,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         let newKeyId: string | null = null;
 
         // create a new SSSS key and set it as default
-        const createSSSS = async (opts: IAddSecretStorageKeyOpts, privateKey?: Uint8Array) => {
+        const createSSSS = async (opts: IAddSecretStorageKeyOpts, privateKey?: Uint8Array): Promise<string> => {
             if (privateKey) {
                 opts.key = privateKey;
             }
@@ -884,7 +884,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
             return keyId;
         };
 
-        const ensureCanCheckPassphrase = async (keyId: string, keyInfo: ISecretStorageKeyInfo) => {
+        const ensureCanCheckPassphrase = async (keyId: string, keyInfo: ISecretStorageKeyInfo): Promise<void> => {
             if (!keyInfo.mac) {
                 const key = await this.baseApis.cryptoCallbacks.getSecretStorageKey?.(
                     { keys: { [keyId]: keyInfo } }, "",
@@ -903,7 +903,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
             }
         };
 
-        const signKeyBackupWithCrossSigning = async (keyBackupAuthData: IKeyBackupInfo["auth_data"]) => {
+        const signKeyBackupWithCrossSigning = async (keyBackupAuthData: IKeyBackupInfo["auth_data"]): Promise<void> => {
             if (
                 this.crossSigningInfo.getId() &&
                 await this.crossSigningInfo.isStoredInKeyCache("master")
@@ -1241,7 +1241,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         const signedDevice = await this.crossSigningInfo.signDevice(this.userId, device);
         logger.info(`Starting background key sig upload for ${this.deviceId}`);
 
-        const upload = ({ shouldEmit = false }) => {
+        const upload = ({ shouldEmit = false }): Promise<void> => {
             return this.baseApis.uploadKeySignatures({
                 [this.userId]: {
                     [this.deviceId]: signedDevice!,
@@ -1475,7 +1475,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     /*
      * Event handler for DeviceList's userNewDevices event
      */
-    private onDeviceListUserCrossSigningUpdated = async (userId: string) => {
+    private onDeviceListUserCrossSigningUpdated = async (userId: string): Promise<void> => {
         if (userId === this.userId) {
             // An update to our own cross-signing key.
             // Get the new key first:
@@ -1657,7 +1657,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
 
         const keysToUpload = Object.keys(keySignatures);
         if (keysToUpload.length) {
-            const upload = ({ shouldEmit = false }) => {
+            const upload = ({ shouldEmit = false }): Promise<void> => {
                 logger.info(`Starting background key sig upload for ${keysToUpload}`);
                 return this.baseApis.uploadKeySignatures({ [this.userId]: keySignatures })
                     .then((response) => {
@@ -1864,7 +1864,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         }
     }
 
-    public setNeedsNewFallback(needsNewFallback: boolean) {
+    public setNeedsNewFallback(needsNewFallback: boolean): void {
         this.needsNewFallback = needsNewFallback;
     }
 
@@ -1873,7 +1873,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     // check if it's time to upload one-time keys, and do so if so.
-    private maybeUploadOneTimeKeys() {
+    private maybeUploadOneTimeKeys(): void {
         // frequency with which to check & upload one-time keys
         const uploadPeriod = 1000 * 60; // one minute
 
@@ -1919,7 +1919,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         // out stale private keys that won't receive a message.
         const keyLimit = Math.floor(maxOneTimeKeys / 2);
 
-        const uploadLoop = async (keyCount: number) => {
+        const uploadLoop = async (keyCount: number): Promise<void> => {
             while (keyLimit > keyCount || this.getNeedsNewFallback()) {
                 // Ask olm to generate new one time keys, then upload them to synapse.
                 if (keyLimit > keyCount) {
@@ -2155,7 +2155,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
                 );
                 const device = await this.crossSigningInfo.signUser(xsk);
                 if (device) {
-                    const upload = async ({ shouldEmit = false }) => {
+                    const upload = async ({ shouldEmit = false }): Promise<void> => {
                         logger.info("Uploading signature for " + userId + "...");
                         const response = await this.baseApis.uploadKeySignatures({
                             [userId]: {
@@ -2246,7 +2246,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
             }
 
             if (device) {
-                const upload = async ({ shouldEmit = false }) => {
+                const upload = async ({ shouldEmit = false }): Promise<void> => {
                     logger.info("Uploading signature for " + deviceId);
                     const response = await this.baseApis.uploadKeySignatures({
                         [userId]: {
@@ -2645,7 +2645,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
      * @returns {Promise} when all devices for the room have been fetched and marked to track
      */
     public trackRoomDevices(roomId: string): Promise<void> {
-        const trackMembers = async () => {
+        const trackMembers = async (): Promise<void> => {
             // not an encrypted room
             if (!this.roomEncryptors.has(roomId)) {
                 return;
@@ -2747,7 +2747,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         let failures = 0;
         const total = keys.length;
 
-        function updateProgress() {
+        function updateProgress(): void {
             opts.progressCallback?.({
                 stage: "load_keys",
                 successes,
@@ -3187,7 +3187,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         }
     }
 
-    private onMembership = (event: MatrixEvent, member: RoomMember, oldMembership?: string) => {
+    private onMembership = (event: MatrixEvent, member: RoomMember, oldMembership?: string): void => {
         try {
             this.onRoomMembership(event, member, oldMembership);
         } catch (e) {
@@ -3340,7 +3340,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         if (!InRoomChannel.validateEvent(event, this.baseApis)) {
             return;
         }
-        const createRequest = (event: MatrixEvent) => {
+        const createRequest = (event: MatrixEvent): VerificationRequest => {
             const channel = new InRoomChannel(this.baseApis, event.getRoomId()!);
             return new VerificationRequest(
                 channel, this.verificationMethods, this.baseApis);
@@ -3361,7 +3361,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
             try {
                 await new Promise<void>((resolve, reject) => {
                     eventIdListener = resolve;
-                    statusListener = () => {
+                    statusListener = (): void => {
                         if (event.status == EventStatus.CANCELLED) {
                             reject(new Error("Event status set to CANCELLED."));
                         }
@@ -3420,7 +3420,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         // retry decryption for all events sent by the sender_key.  This will
         // update the events to show a message indicating that the olm session was
         // wedged.
-        const retryDecryption = () => {
+        const retryDecryption = (): void => {
             const roomDecryptors = this.getRoomDecryptors(olmlib.MEGOLM_ALGORITHM);
             for (const decryptor of roomDecryptors) {
                 decryptor.retryDecryptionFromSender(deviceKey);
@@ -3692,7 +3692,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
             return;
         }
 
-        req.share = () => {
+        req.share = (): void => {
             decryptor.shareKeysWithDevice(req);
         };
 
@@ -3863,14 +3863,14 @@ export class IncomingRoomKeyRequest {
     public readonly requestBody: IRoomKeyRequestBody;
     public share: () => void;
 
-    constructor(event: MatrixEvent) {
+    public constructor(event: MatrixEvent) {
         const content = event.getContent();
 
         this.userId = event.getSender()!;
         this.deviceId = content.requesting_device_id;
         this.requestId = content.request_id;
         this.requestBody = content.body || {};
-        this.share = () => {
+        this.share = (): void => {
             throw new Error("don't know how to share keys for this request yet");
         };
     }
@@ -3888,7 +3888,7 @@ class IncomingRoomKeyRequestCancellation {
     public readonly deviceId: string;
     public readonly requestId: string;
 
-    constructor(event: MatrixEvent) {
+    public constructor(event: MatrixEvent) {
         const content = event.getContent();
 
         this.userId = event.getSender()!;
diff --git a/src/crypto/olmlib.ts b/src/crypto/olmlib.ts
index b77c0b16f..111e4c16d 100644
--- a/src/crypto/olmlib.ts
+++ b/src/crypto/olmlib.ts
@@ -82,7 +82,7 @@ export async function encryptMessageForDevice(
     recipientUserId: string,
     recipientDevice: DeviceInfo,
     payloadFields: Record<string, any>,
-) {
+): Promise<void> {
     const deviceKey = recipientDevice.getIdentityKey();
     const sessionId = await olmDevice.getSessionIdForDevice(deviceKey);
     if (sessionId === null) {
@@ -173,7 +173,7 @@ export async function getExistingOlmSessions(
         for (const deviceInfo of devices) {
             const deviceId = deviceInfo.deviceId;
             const key = deviceInfo.getIdentityKey();
-            promises.push((async () => {
+            promises.push((async (): Promise<void> => {
                 const sessionId = await olmDevice.getSessionIdForDevice(
                     key, true,
                 );
@@ -256,7 +256,7 @@ export async function ensureOlmSessionsForDevices(
                 // conditions.  If we find that we already have a session, then
                 // we'll resolve
                 olmDevice.sessionsInProgress[key] = new Promise(resolve => {
-                    resolveSession[key] = (v: any) => {
+                    resolveSession[key] = (v: any): void => {
                         delete olmDevice.sessionsInProgress[key];
                         resolve(v);
                     };
@@ -463,7 +463,7 @@ export async function verifySignature(
     signingUserId: string,
     signingDeviceId: string,
     signingKey: string,
-) {
+): Promise<void> {
     const signKeyId = "ed25519:" + signingDeviceId;
     const signatures = obj.signatures || {};
     const userSigs = signatures[signingUserId] || {};
@@ -527,7 +527,7 @@ export function pkSign(obj: IObject, key: PkSigning, userId: string, pubKey: str
  * @param {string} pubKey The public key to use to verify
  * @param {string} userId The user ID who signed the object
  */
-export function pkVerify(obj: IObject, pubKey: string, userId: string) {
+export function pkVerify(obj: IObject, pubKey: string, userId: string): void {
     const keyId = "ed25519:" + pubKey;
     if (!(obj.signatures && obj.signatures[userId] && obj.signatures[userId][keyId])) {
         throw new Error("No signature");
diff --git a/src/crypto/store/indexeddb-crypto-store-backend.ts b/src/crypto/store/indexeddb-crypto-store-backend.ts
index f525c0c95..cdf35e787 100644
--- a/src/crypto/store/indexeddb-crypto-store-backend.ts
+++ b/src/crypto/store/indexeddb-crypto-store-backend.ts
@@ -48,11 +48,11 @@ export class Backend implements CryptoStore {
     /**
      * @param {IDBDatabase} db
      */
-    constructor(private db: IDBDatabase) {
+    public constructor(private db: IDBDatabase) {
         // make sure we close the db on `onversionchange` - otherwise
         // attempts to delete the database will block (and subsequent
         // attempts to re-create it will also block).
-        db.onversionchange = () => {
+        db.onversionchange = (): void => {
             logger.log(`versionchange for indexeddb ${this.db.name}: closing`);
             db.close();
         };
@@ -103,7 +103,7 @@ export class Backend implements CryptoStore {
                     `enqueueing key request for ${requestBody.room_id} / ` +
                         requestBody.session_id,
                 );
-                txn.oncomplete = () => {resolve(request);};
+                txn.oncomplete = (): void => {resolve(request);};
                 const store = txn.objectStore("outgoingRoomKeyRequests");
                 store.add(request);
             });
@@ -157,7 +157,7 @@ export class Backend implements CryptoStore {
             requestBody.session_id,
         ]);
 
-        cursorReq.onsuccess = () => {
+        cursorReq.onsuccess = (): void => {
             const cursor = cursorReq.result;
             if (!cursor) {
                 // no match found
@@ -201,7 +201,7 @@ export class Backend implements CryptoStore {
         let stateIndex = 0;
         let result: OutgoingRoomKeyRequest;
 
-        function onsuccess(this: IDBRequest<IDBCursorWithValue | null>) {
+        function onsuccess(this: IDBRequest<IDBCursorWithValue | null>): void {
             const cursor = this.result;
             if (cursor) {
                 // got a match
@@ -243,8 +243,8 @@ export class Backend implements CryptoStore {
             const index = store.index("state");
             const request = index.getAll(wantedState);
 
-            request.onsuccess = () => resolve(request.result);
-            request.onerror = () => reject(request.error);
+            request.onsuccess = (): void => resolve(request.result);
+            request.onerror = (): void => reject(request.error);
         });
     }
 
@@ -256,7 +256,7 @@ export class Backend implements CryptoStore {
         let stateIndex = 0;
         const results: OutgoingRoomKeyRequest[] = [];
 
-        function onsuccess(this: IDBRequest<IDBCursorWithValue | null>) {
+        function onsuccess(this: IDBRequest<IDBCursorWithValue | null>): void {
             const cursor = this.result;
             if (cursor) {
                 const keyReq = cursor.value;
@@ -309,7 +309,7 @@ export class Backend implements CryptoStore {
     ): Promise<OutgoingRoomKeyRequest | null> {
         let result: OutgoingRoomKeyRequest | null = null;
 
-        function onsuccess(this: IDBRequest<IDBCursorWithValue | null>) {
+        function onsuccess(this: IDBRequest<IDBCursorWithValue | null>): void {
             const cursor = this.result;
             if (!cursor) {
                 return;
@@ -348,7 +348,7 @@ export class Backend implements CryptoStore {
     ): Promise<OutgoingRoomKeyRequest | null> {
         const txn = this.db.transaction("outgoingRoomKeyRequests", "readwrite");
         const cursorReq = txn.objectStore("outgoingRoomKeyRequests").openCursor(requestId);
-        cursorReq.onsuccess = () => {
+        cursorReq.onsuccess = (): void => {
             const cursor = cursorReq.result;
             if (!cursor) {
                 return;
@@ -371,7 +371,7 @@ export class Backend implements CryptoStore {
     public getAccount(txn: IDBTransaction, func: (accountPickle: string | null) => void): void {
         const objectStore = txn.objectStore("account");
         const getReq = objectStore.get("-");
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             try {
                 func(getReq.result || null);
             } catch (e) {
@@ -391,7 +391,7 @@ export class Backend implements CryptoStore {
     ): void {
         const objectStore = txn.objectStore("account");
         const getReq = objectStore.get("crossSigningKeys");
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             try {
                 func(getReq.result || null);
             } catch (e) {
@@ -407,7 +407,7 @@ export class Backend implements CryptoStore {
     ): void {
         const objectStore = txn.objectStore("account");
         const getReq = objectStore.get(`ssss_cache:${type}`);
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             try {
                 func(getReq.result || null);
             } catch (e) {
@@ -435,7 +435,7 @@ export class Backend implements CryptoStore {
     public countEndToEndSessions(txn: IDBTransaction, func: (count: number) => void): void {
         const objectStore = txn.objectStore("sessions");
         const countReq = objectStore.count();
-        countReq.onsuccess = function() {
+        countReq.onsuccess = function(): void {
             try {
                 func(countReq.result);
             } catch (e) {
@@ -453,7 +453,7 @@ export class Backend implements CryptoStore {
         const idx = objectStore.index("deviceKey");
         const getReq = idx.openCursor(deviceKey);
         const results: Parameters<Parameters<Backend["getEndToEndSessions"]>[2]>[0] = {};
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             const cursor = getReq.result;
             if (cursor) {
                 results[cursor.value.sessionId] = {
@@ -479,7 +479,7 @@ export class Backend implements CryptoStore {
     ): void {
         const objectStore = txn.objectStore("sessions");
         const getReq = objectStore.get([deviceKey, sessionId]);
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             try {
                 if (getReq.result) {
                     func({
@@ -498,7 +498,7 @@ export class Backend implements CryptoStore {
     public getAllEndToEndSessions(txn: IDBTransaction, func: (session: ISessionInfo | null) => void): void {
         const objectStore = txn.objectStore("sessions");
         const getReq = objectStore.openCursor();
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             try {
                 const cursor = getReq.result;
                 if (cursor) {
@@ -546,7 +546,7 @@ export class Backend implements CryptoStore {
         const objectStore = txn.objectStore("session_problems");
         const index = objectStore.index("deviceKey");
         const req = index.getAll(deviceKey);
-        req.onsuccess = () => {
+        req.onsuccess = (): void => {
             const problems = req.result;
             if (!problems.length) {
                 result = null;
@@ -583,7 +583,7 @@ export class Backend implements CryptoStore {
             return new Promise<void>((resolve) => {
                 const { userId, deviceInfo } = device;
                 const getReq = objectStore.get([userId, deviceInfo.deviceId]);
-                getReq.onsuccess = function() {
+                getReq.onsuccess = function(): void {
                     if (!getReq.result) {
                         objectStore.put({ userId, deviceId: deviceInfo.deviceId });
                         ret.push(device);
@@ -608,7 +608,7 @@ export class Backend implements CryptoStore {
         let withheld: IWithheld | null | boolean = false;
         const objectStore = txn.objectStore("inbound_group_sessions");
         const getReq = objectStore.get([senderCurve25519Key, sessionId]);
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             try {
                 if (getReq.result) {
                     session = getReq.result.session;
@@ -625,7 +625,7 @@ export class Backend implements CryptoStore {
 
         const withheldObjectStore = txn.objectStore("inbound_group_sessions_withheld");
         const withheldGetReq = withheldObjectStore.get([senderCurve25519Key, sessionId]);
-        withheldGetReq.onsuccess = function() {
+        withheldGetReq.onsuccess = function(): void {
             try {
                 if (withheldGetReq.result) {
                     withheld = withheldGetReq.result.session;
@@ -644,7 +644,7 @@ export class Backend implements CryptoStore {
     public getAllEndToEndInboundGroupSessions(txn: IDBTransaction, func: (session: ISession | null) => void): void {
         const objectStore = txn.objectStore("inbound_group_sessions");
         const getReq = objectStore.openCursor();
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             const cursor = getReq.result;
             if (cursor) {
                 try {
@@ -677,7 +677,7 @@ export class Backend implements CryptoStore {
         const addReq = objectStore.add({
             senderCurve25519Key, sessionId, session: sessionData,
         });
-        addReq.onerror = (ev) => {
+        addReq.onerror = (ev): void => {
             if (addReq.error?.name === 'ConstraintError') {
                 // This stops the error from triggering the txn's onerror
                 ev.stopPropagation();
@@ -722,7 +722,7 @@ export class Backend implements CryptoStore {
     public getEndToEndDeviceData(txn: IDBTransaction, func: (deviceData: IDeviceData | null) => void): void {
         const objectStore = txn.objectStore("device_data");
         const getReq = objectStore.get("-");
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             try {
                 func(getReq.result || null);
             } catch (e) {
@@ -745,7 +745,7 @@ export class Backend implements CryptoStore {
         const rooms: Parameters<Parameters<Backend["getEndToEndRooms"]>[1]>[0] = {};
         const objectStore = txn.objectStore("rooms");
         const getReq = objectStore.openCursor();
-        getReq.onsuccess = function() {
+        getReq.onsuccess = function(): void {
             const cursor = getReq.result;
             if (cursor) {
                 rooms[cursor.key as string] = cursor.value;
@@ -771,17 +771,17 @@ export class Backend implements CryptoStore {
                 "readonly",
             );
             txn.onerror = reject;
-            txn.oncomplete = function() {
+            txn.oncomplete = function(): void {
                 resolve(sessions);
             };
             const objectStore = txn.objectStore("sessions_needing_backup");
             const sessionStore = txn.objectStore("inbound_group_sessions");
             const getReq = objectStore.openCursor();
-            getReq.onsuccess = function() {
+            getReq.onsuccess = function(): void {
                 const cursor = getReq.result;
                 if (cursor) {
                     const sessionGetReq = sessionStore.get(cursor.key);
-                    sessionGetReq.onsuccess = function() {
+                    sessionGetReq.onsuccess = function(): void {
                         sessions.push({
                             senderKey: sessionGetReq.result.senderCurve25519Key,
                             sessionId: sessionGetReq.result.sessionId,
@@ -804,7 +804,7 @@ export class Backend implements CryptoStore {
         return new Promise((resolve, reject) => {
             const req = objectStore.count();
             req.onerror = reject;
-            req.onsuccess = () => resolve(req.result);
+            req.onsuccess = (): void => resolve(req.result);
         });
     }
 
@@ -852,7 +852,7 @@ export class Backend implements CryptoStore {
         }
         const objectStore = txn.objectStore("shared_history_inbound_group_sessions");
         const req = objectStore.get([roomId]);
-        req.onsuccess = () => {
+        req.onsuccess = (): void => {
             const { sessions } = req.result || { sessions: [] };
             sessions.push([senderKey, sessionId]);
             objectStore.put({ roomId, sessions });
@@ -871,7 +871,7 @@ export class Backend implements CryptoStore {
         const objectStore = txn.objectStore("shared_history_inbound_group_sessions");
         const req = objectStore.get([roomId]);
         return new Promise((resolve, reject) => {
-            req.onsuccess = () => {
+            req.onsuccess = (): void => {
                 const { sessions } = req.result || { sessions: [] };
                 resolve(sessions);
             };
@@ -891,7 +891,7 @@ export class Backend implements CryptoStore {
         }
         const objectStore = txn.objectStore("parked_shared_history");
         const req = objectStore.get([roomId]);
-        req.onsuccess = () => {
+        req.onsuccess = (): void => {
             const { parked } = req.result || { parked: [] };
             parked.push(parkedData);
             objectStore.put({ roomId, parked });
@@ -909,7 +909,7 @@ export class Backend implements CryptoStore {
         }
         const cursorReq = txn.objectStore("parked_shared_history").openCursor(roomId);
         return new Promise((resolve, reject) => {
-            cursorReq.onsuccess = () => {
+            cursorReq.onsuccess = (): void => {
                 const cursor = cursorReq.result;
                 if (!cursor) {
                     resolve([]);
@@ -957,32 +957,32 @@ export class Backend implements CryptoStore {
 
 type DbMigration = (db: IDBDatabase) => void;
 const DB_MIGRATIONS: DbMigration[] = [
-    (db) => { createDatabase(db); },
-    (db) => { db.createObjectStore("account"); },
-    (db) => {
+    (db): void => { createDatabase(db); },
+    (db): void => { db.createObjectStore("account"); },
+    (db): void => {
         const sessionsStore = db.createObjectStore("sessions", {
             keyPath: ["deviceKey", "sessionId"],
         });
         sessionsStore.createIndex("deviceKey", "deviceKey");
     },
-    (db) => {
+    (db): void => {
         db.createObjectStore("inbound_group_sessions", {
             keyPath: ["senderCurve25519Key", "sessionId"],
         });
     },
-    (db) => { db.createObjectStore("device_data"); },
-    (db) => { db.createObjectStore("rooms"); },
-    (db) => {
+    (db): void => { db.createObjectStore("device_data"); },
+    (db): void => { db.createObjectStore("rooms"); },
+    (db): void => {
         db.createObjectStore("sessions_needing_backup", {
             keyPath: ["senderCurve25519Key", "sessionId"],
         });
     },
-    (db) => {
+    (db): void => {
         db.createObjectStore("inbound_group_sessions_withheld", {
             keyPath: ["senderCurve25519Key", "sessionId"],
         });
     },
-    (db) => {
+    (db): void => {
         const problemsStore = db.createObjectStore("session_problems", {
             keyPath: ["deviceKey", "time"],
         });
@@ -992,12 +992,12 @@ const DB_MIGRATIONS: DbMigration[] = [
             keyPath: ["userId", "deviceId"],
         });
     },
-    (db) => {
+    (db): void => {
         db.createObjectStore("shared_history_inbound_group_sessions", {
             keyPath: ["roomId"],
         });
     },
-    (db) => {
+    (db): void => {
         db.createObjectStore("parked_shared_history", {
             keyPath: ["roomId"],
         });
@@ -1037,7 +1037,7 @@ interface IWrappedIDBTransaction extends IDBTransaction {
  * Aborts a transaction with a given exception
  * The transaction promise will be rejected with this exception.
  */
-function abortWithException(txn: IDBTransaction, e: Error) {
+function abortWithException(txn: IDBTransaction, e: Error): void {
     // We cheekily stick our exception onto the transaction object here
     // We could alternatively make the thing we pass back to the app
     // an object containing the transaction and exception.
@@ -1052,13 +1052,13 @@ function abortWithException(txn: IDBTransaction, e: Error) {
 
 function promiseifyTxn<T>(txn: IDBTransaction): Promise<T | null> {
     return new Promise((resolve, reject) => {
-        txn.oncomplete = () => {
+        txn.oncomplete = (): void => {
             if ((txn as IWrappedIDBTransaction)._mx_abortexception !== undefined) {
                 reject((txn as IWrappedIDBTransaction)._mx_abortexception);
             }
             resolve(null);
         };
-        txn.onerror = (event) => {
+        txn.onerror = (event): void => {
             if ((txn as IWrappedIDBTransaction)._mx_abortexception !== undefined) {
                 reject((txn as IWrappedIDBTransaction)._mx_abortexception);
             } else {
@@ -1066,7 +1066,7 @@ function promiseifyTxn<T>(txn: IDBTransaction): Promise<T | null> {
                 reject(txn.error);
             }
         };
-        txn.onabort = (event) => {
+        txn.onabort = (event): void => {
             if ((txn as IWrappedIDBTransaction)._mx_abortexception !== undefined) {
                 reject((txn as IWrappedIDBTransaction)._mx_abortexception);
             } else {
diff --git a/src/crypto/store/indexeddb-crypto-store.ts b/src/crypto/store/indexeddb-crypto-store.ts
index 4fbeafe19..d743a95de 100644
--- a/src/crypto/store/indexeddb-crypto-store.ts
+++ b/src/crypto/store/indexeddb-crypto-store.ts
@@ -73,7 +73,7 @@ export class IndexedDBCryptoStore implements CryptoStore {
      * @param {IDBFactory} indexedDB  global indexedDB instance
      * @param {string} dbName   name of db to connect to
      */
-    constructor(private readonly indexedDB: IDBFactory, private readonly dbName: string) {}
+    public constructor(private readonly indexedDB: IDBFactory, private readonly dbName: string) {}
 
     /**
      * Ensure the database exists and is up-to-date, or fall back to
@@ -99,24 +99,24 @@ export class IndexedDBCryptoStore implements CryptoStore {
 
             const req = this.indexedDB.open(this.dbName, IndexedDBCryptoStoreBackend.VERSION);
 
-            req.onupgradeneeded = (ev) => {
+            req.onupgradeneeded = (ev): void => {
                 const db = req.result;
                 const oldVersion = ev.oldVersion;
                 IndexedDBCryptoStoreBackend.upgradeDatabase(db, oldVersion);
             };
 
-            req.onblocked = () => {
+            req.onblocked = (): void => {
                 logger.log(
                     `can't yet open IndexedDBCryptoStore because it is open elsewhere`,
                 );
             };
 
-            req.onerror = (ev) => {
+            req.onerror = (ev): void => {
                 logger.log("Error connecting to indexeddb", ev);
                 reject(req.error);
             };
 
-            req.onsuccess = () => {
+            req.onsuccess = (): void => {
                 const db = req.result;
 
                 logger.log(`connected to indexeddb ${this.dbName}`);
@@ -179,18 +179,18 @@ export class IndexedDBCryptoStore implements CryptoStore {
             logger.log(`Removing indexeddb instance: ${this.dbName}`);
             const req = this.indexedDB.deleteDatabase(this.dbName);
 
-            req.onblocked = () => {
+            req.onblocked = (): void => {
                 logger.log(
                     `can't yet delete IndexedDBCryptoStore because it is open elsewhere`,
                 );
             };
 
-            req.onerror = (ev) => {
+            req.onerror = (ev): void => {
                 logger.log("Error deleting data from indexeddb", ev);
                 reject(req.error);
             };
 
-            req.onsuccess = () => {
+            req.onsuccess = (): void => {
                 logger.log(`Removed indexeddb instance: ${this.dbName}`);
                 resolve();
             };
@@ -322,7 +322,7 @@ export class IndexedDBCryptoStore implements CryptoStore {
      * @param {*} txn An active transaction. See doTxn().
      * @param {function(string)} func Called with the account pickle
      */
-    public getAccount(txn: IDBTransaction, func: (accountPickle: string | null) => void) {
+    public getAccount(txn: IDBTransaction, func: (accountPickle: string | null) => void): void {
         this.backend!.getAccount(txn, func);
     }
 
diff --git a/src/crypto/store/localStorage-crypto-store.ts b/src/crypto/store/localStorage-crypto-store.ts
index 4bc8b45ef..977236ef9 100644
--- a/src/crypto/store/localStorage-crypto-store.ts
+++ b/src/crypto/store/localStorage-crypto-store.ts
@@ -76,7 +76,7 @@ export class LocalStorageCryptoStore extends MemoryCryptoStore {
         return false;
     }
 
-    constructor(private readonly store: Storage) {
+    public constructor(private readonly store: Storage) {
         super();
     }
 
@@ -154,7 +154,7 @@ export class LocalStorageCryptoStore extends MemoryCryptoStore {
         setJsonItem(this.store, key, problems);
     }
 
-    async getEndToEndSessionProblem(deviceKey: string, timestamp: number): Promise<IProblem | null> {
+    public async getEndToEndSessionProblem(deviceKey: string, timestamp: number): Promise<IProblem | null> {
         const key = keyEndToEndSessionProblems(deviceKey);
         const problems = getJsonItem<IProblem[]>(this.store, key) || [];
         if (!problems.length) {
@@ -408,7 +408,7 @@ export class LocalStorageCryptoStore extends MemoryCryptoStore {
         setJsonItem(this.store, E2E_PREFIX + `ssss_cache.${type}`, key);
     }
 
-    doTxn<T>(mode: Mode, stores: Iterable<string>, func: (txn: unknown) => T): Promise<T> {
+    public doTxn<T>(mode: Mode, stores: Iterable<string>, func: (txn: unknown) => T): Promise<T> {
         return Promise.resolve(func(null));
     }
 }
diff --git a/src/crypto/store/memory-crypto-store.ts b/src/crypto/store/memory-crypto-store.ts
index 8b0206eef..f22379ee8 100644
--- a/src/crypto/store/memory-crypto-store.ts
+++ b/src/crypto/store/memory-crypto-store.ts
@@ -279,7 +279,7 @@ export class MemoryCryptoStore implements CryptoStore {
 
     // Olm Account
 
-    public getAccount(txn: unknown, func: (accountPickle: string | null) => void) {
+    public getAccount(txn: unknown, func: (accountPickle: string | null) => void): void {
         func(this.account);
     }
 
diff --git a/src/crypto/verification/Base.ts b/src/crypto/verification/Base.ts
index f2fc1d5f9..55b349e99 100644
--- a/src/crypto/verification/Base.ts
+++ b/src/crypto/verification/Base.ts
@@ -34,7 +34,7 @@ import { ListenerMap, TypedEventEmitter } from "../../models/typed-event-emitter
 const timeoutException = new Error("Verification timed out");
 
 export class SwitchStartEventError extends Error {
-    constructor(public readonly startEvent: MatrixEvent | null) {
+    public constructor(public readonly startEvent: MatrixEvent | null) {
         super();
     }
 }
@@ -91,7 +91,7 @@ export class VerificationBase<
      * @param {object} [request] the key verification request object related to
      * this verification, if any
      */
-    constructor(
+    public constructor(
         public readonly channel: IVerificationChannel,
         public readonly baseApis: MatrixClient,
         public readonly userId: string,
@@ -286,12 +286,12 @@ export class VerificationBase<
         if (this.promise) return this.promise;
 
         this.promise = new Promise((resolve, reject) => {
-            this.resolve = (...args) => {
+            this.resolve = (...args): void => {
                 this._done = true;
                 this.endTimer();
                 resolve(...args);
             };
-            this.reject = (e: Error | MatrixEvent) => {
+            this.reject = (e: Error | MatrixEvent): void => {
                 this._done = true;
                 this.endTimer();
                 reject(e);
diff --git a/src/crypto/verification/QRCode.ts b/src/crypto/verification/QRCode.ts
index 9ff9315a9..f6bdda17e 100644
--- a/src/crypto/verification/QRCode.ts
+++ b/src/crypto/verification/QRCode.ts
@@ -154,7 +154,7 @@ interface IQrData {
 }
 
 export class QRCodeData {
-    constructor(
+    public constructor(
         public readonly mode: Mode,
         private readonly sharedSecret: string,
         // only set when mode is MODE_VERIFY_OTHER_USER, master key of other party at time of generating QR code
@@ -283,21 +283,21 @@ export class QRCodeData {
     private static generateBuffer(qrData: IQrData): Buffer {
         let buf = Buffer.alloc(0); // we'll concat our way through life
 
-        const appendByte = (b) => {
+        const appendByte = (b): void => {
             const tmpBuf = Buffer.from([b]);
             buf = Buffer.concat([buf, tmpBuf]);
         };
-        const appendInt = (i) => {
+        const appendInt = (i): void => {
             const tmpBuf = Buffer.alloc(2);
             tmpBuf.writeInt16BE(i, 0);
             buf = Buffer.concat([buf, tmpBuf]);
         };
-        const appendStr = (s, enc, withLengthPrefix = true) => {
+        const appendStr = (s, enc, withLengthPrefix = true): void => {
             const tmpBuf = Buffer.from(s, enc);
             if (withLengthPrefix) appendInt(tmpBuf.byteLength);
             buf = Buffer.concat([buf, tmpBuf]);
         };
-        const appendEncBase64 = (b64) => {
+        const appendEncBase64 = (b64): void => {
             const b = decodeBase64(b64);
             const tmpBuf = Buffer.from(b);
             buf = Buffer.concat([buf, tmpBuf]);
diff --git a/src/crypto/verification/SAS.ts b/src/crypto/verification/SAS.ts
index 806b4bf5e..5df6d48f6 100644
--- a/src/crypto/verification/SAS.ts
+++ b/src/crypto/verification/SAS.ts
@@ -170,10 +170,12 @@ const macMethods = {
     "hmac-sha256": "calculate_mac_long_kdf",
 };
 
-function calculateMAC(olmSAS: OlmSAS, method: string) {
-    return function(...args) {
+type Method = keyof typeof macMethods;
+
+function calculateMAC(olmSAS: OlmSAS, method: Method) {
+    return function(...args): string {
         const macFunction = olmSAS[macMethods[method]];
-        const mac = macFunction.apply(olmSAS, args);
+        const mac: string = macFunction.apply(olmSAS, args);
         logger.log("SAS calculateMAC:", method, args, mac);
         return mac;
     };
@@ -208,7 +210,7 @@ const calculateKeyAgreement = {
  */
 const KEY_AGREEMENT_LIST = ["curve25519-hkdf-sha256", "curve25519"];
 const HASHES_LIST = ["sha256"];
-const MAC_LIST = ["org.matrix.msc3783.hkdf-hmac-sha256", "hkdf-hmac-sha256", "hmac-sha256"];
+const MAC_LIST: Method[] = ["org.matrix.msc3783.hkdf-hmac-sha256", "hkdf-hmac-sha256", "hmac-sha256"];
 const SAS_LIST = Object.keys(sasGenerators);
 
 const KEY_AGREEMENT_SET = new Set(KEY_AGREEMENT_LIST);
@@ -300,13 +302,13 @@ export class SAS extends Base<SasEvent, EventHandlerMap> {
         keyAgreement: string,
         sasMethods: string[],
         olmSAS: OlmSAS,
-        macMethod: string,
+        macMethod: Method,
     ): Promise<void> {
         const sasBytes = calculateKeyAgreement[keyAgreement](this, olmSAS, 6);
         const verifySAS = new Promise<void>((resolve, reject) => {
             this.sasEvent = {
                 sas: generateSas(sasBytes, sasMethods),
-                confirm: async () => {
+                confirm: async (): Promise<void> => {
                     try {
                         await this.sendMAC(olmSAS, macMethod);
                         resolve();
@@ -443,7 +445,7 @@ export class SAS extends Base<SasEvent, EventHandlerMap> {
         }
     }
 
-    private sendMAC(olmSAS: OlmSAS, method: string): Promise<void> {
+    private sendMAC(olmSAS: OlmSAS, method: Method): Promise<void> {
         const mac = {};
         const keyList: string[] = [];
         const baseInfo = "MATRIX_KEY_VERIFICATION_MAC"
@@ -475,7 +477,7 @@ export class SAS extends Base<SasEvent, EventHandlerMap> {
         return this.send(EventType.KeyVerificationMac, { mac, keys });
     }
 
-    private async checkMAC(olmSAS: OlmSAS, content: IContent, method: string): Promise<void> {
+    private async checkMAC(olmSAS: OlmSAS, content: IContent, method: Method): Promise<void> {
         const baseInfo = "MATRIX_KEY_VERIFICATION_MAC"
               + this.userId + this.deviceId
               + this.baseApis.getUserId() + this.baseApis.deviceId
diff --git a/src/crypto/verification/request/InRoomChannel.ts b/src/crypto/verification/request/InRoomChannel.ts
index 2a4fb8d81..664a2dad6 100644
--- a/src/crypto/verification/request/InRoomChannel.ts
+++ b/src/crypto/verification/request/InRoomChannel.ts
@@ -44,7 +44,7 @@ export class InRoomChannel implements IVerificationChannel {
      * @param {string} roomId id of the room where verification events should be posted in, should be a DM with the given user.
      * @param {string} userId id of user that the verification request is directed at, should be present in the room.
      */
-    constructor(
+    public constructor(
         private readonly client: MatrixClient,
         public readonly roomId: string,
         public userId?: string,
diff --git a/src/crypto/verification/request/ToDeviceChannel.ts b/src/crypto/verification/request/ToDeviceChannel.ts
index 112272914..30d615251 100644
--- a/src/crypto/verification/request/ToDeviceChannel.ts
+++ b/src/crypto/verification/request/ToDeviceChannel.ts
@@ -42,7 +42,7 @@ export class ToDeviceChannel implements IVerificationChannel {
     public request?: VerificationRequest;
 
     // userId and devices of user we're about to verify
-    constructor(
+    public constructor(
         private readonly client: MatrixClient,
         public readonly userId: string,
         private readonly devices: string[],
diff --git a/src/crypto/verification/request/VerificationRequest.ts b/src/crypto/verification/request/VerificationRequest.ts
index 2ff71d62c..58de4b9a2 100644
--- a/src/crypto/verification/request/VerificationRequest.ts
+++ b/src/crypto/verification/request/VerificationRequest.ts
@@ -116,7 +116,7 @@ export class VerificationRequest<
     public _cancellingUserId?: string; // Used in tests only
     private _verifier?: VerificationBase<any, any>;
 
-    constructor(
+    public constructor(
         public readonly channel: C,
         private readonly verificationMethods: Map<VerificationMethod, typeof VerificationBase>,
         private readonly client: MatrixClient,
@@ -498,7 +498,7 @@ export class VerificationRequest<
      */
     public waitFor(fn: (request: VerificationRequest) => boolean): Promise<VerificationRequest> {
         return new Promise((resolve, reject) => {
-            const check = () => {
+            const check = (): boolean => {
                 let handled = false;
                 if (fn(this)) {
                     resolve(this);
@@ -539,7 +539,7 @@ export class VerificationRequest<
 
     private calculatePhaseTransitions(): ITransition[] {
         const transitions: ITransition[] = [{ phase: PHASE_UNSENT }];
-        const phase = () => transitions[transitions.length - 1].phase;
+        const phase = (): Phase => transitions[transitions.length - 1].phase;
 
         // always pass by .request first to be sure channel.userId has been set
         const hasRequestByThem = this.eventsByThem.has(REQUEST_TYPE);
@@ -816,7 +816,7 @@ export class VerificationRequest<
         }
     }
 
-    private cancelOnTimeout = async () => {
+    private cancelOnTimeout = async (): Promise<void> => {
         try {
             if (this.initiatedByMe) {
                 await this.cancel({
diff --git a/src/embedded.ts b/src/embedded.ts
index d1dfb50bf..27cf564a6 100644
--- a/src/embedded.ts
+++ b/src/embedded.ts
@@ -101,7 +101,7 @@ export class RoomWidgetClient extends MatrixClient {
     private lifecycle?: AbortController;
     private syncState: SyncState | null = null;
 
-    constructor(
+    public constructor(
         private readonly widgetApi: WidgetApi,
         private readonly capabilities: ICapabilities,
         private readonly roomId: string,
@@ -211,7 +211,7 @@ export class RoomWidgetClient extends MatrixClient {
         if (this.capabilities.turnServers) this.watchTurnServers();
     }
 
-    public stopClient() {
+    public stopClient(): void {
         this.widgetApi.off(`action:${WidgetApiToWidgetAction.SendEvent}`, this.onEvent);
         this.widgetApi.off(`action:${WidgetApiToWidgetAction.SendToDevice}`, this.onToDevice);
 
@@ -288,7 +288,7 @@ export class RoomWidgetClient extends MatrixClient {
         return this.syncState;
     }
 
-    private setSyncState(state: SyncState) {
+    private setSyncState(state: SyncState): void {
         const oldState = this.syncState;
         this.syncState = state;
         this.emit(ClientEvent.Sync, state, oldState);
@@ -298,7 +298,7 @@ export class RoomWidgetClient extends MatrixClient {
         await this.widgetApi.transport.reply<IWidgetApiAcknowledgeResponseData>(ev.detail, {});
     }
 
-    private onEvent = async (ev: CustomEvent<ISendEventToWidgetActionRequest>) => {
+    private onEvent = async (ev: CustomEvent<ISendEventToWidgetActionRequest>): Promise<void> => {
         ev.preventDefault();
 
         // Verify the room ID matches, since it's possible for the client to
@@ -317,7 +317,7 @@ export class RoomWidgetClient extends MatrixClient {
         await this.ack(ev);
     };
 
-    private onToDevice = async (ev: CustomEvent<ISendToDeviceToWidgetActionRequest>) => {
+    private onToDevice = async (ev: CustomEvent<ISendToDeviceToWidgetActionRequest>): Promise<void> => {
         ev.preventDefault();
 
         const event = new MatrixEvent({
@@ -333,9 +333,11 @@ export class RoomWidgetClient extends MatrixClient {
         await this.ack(ev);
     };
 
-    private async watchTurnServers() {
+    private async watchTurnServers(): Promise<void> {
         const servers = this.widgetApi.getTurnServers();
-        const onClientStopped = () => servers.return(undefined);
+        const onClientStopped = (): void => {
+            servers.return(undefined);
+        };
         this.lifecycle!.signal.addEventListener("abort", onClientStopped);
 
         try {
diff --git a/src/event-mapper.ts b/src/event-mapper.ts
index 57d36c9f6..6f2e25c1b 100644
--- a/src/event-mapper.ts
+++ b/src/event-mapper.ts
@@ -29,7 +29,7 @@ export function eventMapperFor(client: MatrixClient, options: MapperOpts): Event
     let preventReEmit = Boolean(options.preventReEmit);
     const decrypt = options.decrypt !== false;
 
-    function mapper(plainOldJsObject: Partial<IEvent>) {
+    function mapper(plainOldJsObject: Partial<IEvent>): MatrixEvent {
         if (options.toDevice) {
             delete plainOldJsObject.room_id;
         }
diff --git a/src/filter-component.ts b/src/filter-component.ts
index 759c97921..85afb0ea7 100644
--- a/src/filter-component.ts
+++ b/src/filter-component.ts
@@ -73,7 +73,7 @@ export interface IFilterComponent {
  * @param {Object} filterJson the definition of this filter JSON, e.g. { 'contains_url': true }
  */
 export class FilterComponent {
-    constructor(private filterJson: IFilterComponent, public readonly userId?: string | undefined | null) {}
+    public constructor(private filterJson: IFilterComponent, public readonly userId?: string | undefined | null) {}
 
     /**
      * Checks with the filter component matches the given event
diff --git a/src/filter.ts b/src/filter.ts
index fb499c4da..57bd0540d 100644
--- a/src/filter.ts
+++ b/src/filter.ts
@@ -31,7 +31,7 @@ import { MatrixEvent } from "./models/event";
  * @param {string} keyNesting
  * @param {*} val
  */
-function setProp(obj: object, keyNesting: string, val: any) {
+function setProp(obj: object, keyNesting: string, val: any): void {
     const nestedKeys = keyNesting.split(".");
     let currentObj = obj;
     for (let i = 0; i < (nestedKeys.length - 1); i++) {
@@ -88,7 +88,7 @@ interface IRoomFilter {
  * @prop {?string} filterId The filter ID
  */
 export class Filter {
-    static LAZY_LOADING_MESSAGES_FILTER = {
+    public static LAZY_LOADING_MESSAGES_FILTER = {
         lazy_load_members: true,
     };
 
@@ -110,7 +110,7 @@ export class Filter {
     private roomFilter?: FilterComponent;
     private roomTimelineFilter?: FilterComponent;
 
-    constructor(public readonly userId: string | undefined | null, public filterId?: string) {}
+    public constructor(public readonly userId: string | undefined | null, public filterId?: string) {}
 
     /**
      * Get the ID of this filter on your homeserver (if known)
@@ -132,7 +132,7 @@ export class Filter {
      * Set the JSON body of the filter
      * @param {Object} definition The filter definition
      */
-    public setDefinition(definition: IFilterDefinition) {
+    public setDefinition(definition: IFilterDefinition): void {
         this.definition = definition;
 
         // This is all ported from synapse's FilterCollection()
@@ -225,7 +225,7 @@ export class Filter {
      * Set the max number of events to return for each room's timeline.
      * @param {Number} limit The max number of events to return for each room.
      */
-    public setTimelineLimit(limit: number) {
+    public setTimelineLimit(limit: number): void {
         setProp(this.definition, "room.timeline.limit", limit);
     }
 
@@ -255,7 +255,7 @@ export class Filter {
      * @param {boolean} includeLeave True to make rooms the user has left appear
      * in responses.
      */
-    public setIncludeLeaveRooms(includeLeave: boolean) {
+    public setIncludeLeaveRooms(includeLeave: boolean): void {
         setProp(this.definition, "room.include_leave", includeLeave);
     }
 }
diff --git a/src/http-api/errors.ts b/src/http-api/errors.ts
index be63c94fd..5ae0a0f50 100644
--- a/src/http-api/errors.ts
+++ b/src/http-api/errors.ts
@@ -31,7 +31,7 @@ interface IErrorJson extends Partial<IUsageLimit> {
  * @param {number} httpStatus The HTTP response status code.
  */
 export class HTTPError extends Error {
-    constructor(msg: string, public readonly httpStatus?: number) {
+    public constructor(msg: string, public readonly httpStatus?: number) {
         super(msg);
     }
 }
@@ -51,7 +51,7 @@ export class MatrixError extends HTTPError {
     public readonly errcode?: string;
     public data: IErrorJson;
 
-    constructor(
+    public constructor(
         errorJson: IErrorJson = {},
         public readonly httpStatus?: number,
         public url?: string,
@@ -79,11 +79,11 @@ export class MatrixError extends HTTPError {
  * @constructor
  */
 export class ConnectionError extends Error {
-    constructor(message: string, cause?: Error) {
+    public constructor(message: string, cause?: Error) {
         super(message + (cause ? `: ${cause.message}` : ""));
     }
 
-    get name() {
+    public get name(): string {
         return "ConnectionError";
     }
 }
diff --git a/src/http-api/fetch.ts b/src/http-api/fetch.ts
index 92413c094..71ba098e3 100644
--- a/src/http-api/fetch.ts
+++ b/src/http-api/fetch.ts
@@ -41,7 +41,7 @@ export type ResponseType<T, O extends IHttpOpts> =
 export class FetchHttpApi<O extends IHttpOpts> {
     private abortController = new AbortController();
 
-    constructor(
+    public constructor(
         private eventEmitter: TypedEventEmitter<HttpApiEvent, HttpApiEventHandlerMap>,
         public readonly opts: O,
     ) {
diff --git a/src/http-api/index.ts b/src/http-api/index.ts
index 0c9b0b623..c7f782d89 100644
--- a/src/http-api/index.ts
+++ b/src/http-api/index.ts
@@ -77,7 +77,7 @@ export class MatrixHttpApi<O extends IHttpOpts> extends FetchHttpApi<O> {
         if (global.XMLHttpRequest) {
             const xhr = new global.XMLHttpRequest();
 
-            const timeoutFn = function() {
+            const timeoutFn = function(): void {
                 xhr.abort();
                 defer.reject(new Error("Timeout"));
             };
@@ -85,7 +85,7 @@ export class MatrixHttpApi<O extends IHttpOpts> extends FetchHttpApi<O> {
             // set an initial timeout of 30s; we'll advance it each time we get a progress notification
             let timeoutTimer = callbacks.setTimeout(timeoutFn, 30000);
 
-            xhr.onreadystatechange = function() {
+            xhr.onreadystatechange = function(): void {
                 switch (xhr.readyState) {
                     case global.XMLHttpRequest.DONE:
                         callbacks.clearTimeout(timeoutTimer);
@@ -113,7 +113,7 @@ export class MatrixHttpApi<O extends IHttpOpts> extends FetchHttpApi<O> {
                 }
             };
 
-            xhr.upload.onprogress = (ev: ProgressEvent) => {
+            xhr.upload.onprogress = (ev: ProgressEvent): void => {
                 callbacks.clearTimeout(timeoutTimer);
                 upload.loaded = ev.loaded;
                 upload.total = ev.total;
diff --git a/src/http-api/utils.ts b/src/http-api/utils.ts
index c7e394770..504660950 100644
--- a/src/http-api/utils.ts
+++ b/src/http-api/utils.ts
@@ -36,13 +36,13 @@ export function anySignal(signals: AbortSignal[]): {
 } {
     const controller = new AbortController();
 
-    function cleanup() {
+    function cleanup(): void {
         for (const signal of signals) {
             signal.removeEventListener("abort", onAbort);
         }
     }
 
-    function onAbort() {
+    function onAbort(): void {
         controller.abort();
         cleanup();
     }
diff --git a/src/indexeddb-helpers.ts b/src/indexeddb-helpers.ts
index 84de7c0e9..695a3145f 100644
--- a/src/indexeddb-helpers.ts
+++ b/src/indexeddb-helpers.ts
@@ -26,13 +26,13 @@ export function exists(indexedDB: IDBFactory, dbName: string): Promise<boolean>
     return new Promise<boolean>((resolve, reject) => {
         let exists = true;
         const req = indexedDB.open(dbName);
-        req.onupgradeneeded = () => {
+        req.onupgradeneeded = (): void => {
             // Since we did not provide an explicit version when opening, this event
             // should only fire if the DB did not exist before at any version.
             exists = false;
         };
-        req.onblocked = () => reject(req.error);
-        req.onsuccess = () => {
+        req.onblocked = (): void => reject(req.error);
+        req.onsuccess = (): void => {
             const db = req.result;
             db.close();
             if (!exists) {
@@ -45,6 +45,6 @@ export function exists(indexedDB: IDBFactory, dbName: string): Promise<boolean>
             }
             resolve(exists);
         };
-        req.onerror = ev => reject(req.error);
+        req.onerror = (): void => reject(req.error);
     });
 }
diff --git a/src/interactive-auth.ts b/src/interactive-auth.ts
index 80f3e95cf..df4a42c27 100644
--- a/src/interactive-auth.ts
+++ b/src/interactive-auth.ts
@@ -100,7 +100,7 @@ class NoAuthFlowFoundError extends Error {
     public name = "NoAuthFlowFoundError";
 
     // eslint-disable-next-line @typescript-eslint/naming-convention, camelcase
-    constructor(m: string, public readonly required_stages: string[], public readonly flows: IFlow[]) {
+    public constructor(m: string, public readonly required_stages: string[], public readonly flows: IFlow[]) {
         super(m);
     }
 }
@@ -218,7 +218,7 @@ export class InteractiveAuth {
     // the promise the will resolve/reject when it completes
     private submitPromise: Promise<void> | null = null;
 
-    constructor(opts: IOpts) {
+    public constructor(opts: IOpts) {
         this.matrixClient = opts.matrixClient;
         this.data = opts.authData || {};
         this.requestCallback = opts.doRequest;
@@ -419,7 +419,7 @@ export class InteractiveAuth {
     /**
      * Requests a new email token and sets the email sid for the validation session
      */
-    public requestEmailToken = async () => {
+    public requestEmailToken = async (): Promise<void> => {
         if (!this.requestingEmailToken) {
             logger.trace("Requesting email token. Attempt: " + this.emailAttempt);
             // If we've picked a flow with email auth, we send the email
diff --git a/src/logger.ts b/src/logger.ts
index f2fb82167..de1ca6619 100644
--- a/src/logger.ts
+++ b/src/logger.ts
@@ -35,7 +35,7 @@ const DEFAULT_NAMESPACE = "matrix";
 // console methods at initialization time by a factory that looks up the console methods
 // when logging so we always get the current value of console methods.
 log.methodFactory = function(methodName, logLevel, loggerName) {
-    return function(this: PrefixedLogger, ...args) {
+    return function(this: PrefixedLogger, ...args): void {
         /* eslint-disable @typescript-eslint/no-invalid-this */
         if (this.prefix) {
             args.unshift(this.prefix);
@@ -67,7 +67,7 @@ export interface PrefixedLogger extends Logger {
     prefix: string;
 }
 
-function extendLogger(logger: Logger) {
+function extendLogger(logger: Logger): void {
     (<PrefixedLogger>logger).withPrefix = function(prefix: string): PrefixedLogger {
         const existingPrefix = this.prefix || "";
         return getPrefixedLogger(existingPrefix + prefix);
diff --git a/src/matrix.ts b/src/matrix.ts
index e89feddeb..421e0e6ed 100644
--- a/src/matrix.ts
+++ b/src/matrix.ts
@@ -21,6 +21,7 @@ import { MemoryStore } from "./store/memory";
 import { MatrixScheduler } from "./scheduler";
 import { MatrixClient, ICreateClientOpts } from "./client";
 import { RoomWidgetClient, ICapabilities } from "./embedded";
+import { CryptoStore } from "./crypto/store/base";
 
 export * from "./client";
 export * from "./embedded";
@@ -64,7 +65,7 @@ export {
 } from "./webrtc/groupCall";
 export type { GroupCall } from "./webrtc/groupCall";
 
-let cryptoStoreFactory = () => new MemoryCryptoStore;
+let cryptoStoreFactory = (): CryptoStore => new MemoryCryptoStore;
 
 /**
  * Configure a different factory to be used for creating crypto stores
@@ -72,7 +73,7 @@ let cryptoStoreFactory = () => new MemoryCryptoStore;
  * @param {Function} fac  a function which will return a new
  *    {@link module:crypto.store.base~CryptoStore}.
  */
-export function setCryptoStoreFactory(fac) {
+export function setCryptoStoreFactory(fac: () => CryptoStore): void {
     cryptoStoreFactory = fac;
 }
 
diff --git a/src/models/MSC3089TreeSpace.ts b/src/models/MSC3089TreeSpace.ts
index 762ef586a..f437eab84 100644
--- a/src/models/MSC3089TreeSpace.ts
+++ b/src/models/MSC3089TreeSpace.ts
@@ -172,7 +172,7 @@ export class MSC3089TreeSpace {
         const currentPls = this.room.currentState.getStateEvents(EventType.RoomPowerLevels, "");
         if (Array.isArray(currentPls)) throw new Error("Unexpected return type for power levels");
 
-        const pls = currentPls.getContent() || {};
+        const pls = currentPls?.getContent() || {};
         const viewLevel = pls['users_default'] || 0;
         const editLevel = pls['events_default'] || 50;
         const adminLevel = pls['events']?.[EventType.RoomPowerLevels] || 100;
@@ -207,7 +207,7 @@ export class MSC3089TreeSpace {
         const currentPls = this.room.currentState.getStateEvents(EventType.RoomPowerLevels, "");
         if (Array.isArray(currentPls)) throw new Error("Unexpected return type for power levels");
 
-        const pls = currentPls.getContent() || {};
+        const pls = currentPls?.getContent() || {};
         const viewLevel = pls['users_default'] || 0;
         const editLevel = pls['events_default'] || 50;
         const adminLevel = pls['events']?.[EventType.RoomPowerLevels] || 100;
diff --git a/src/models/beacon.ts b/src/models/beacon.ts
index fc817b05e..6e20b229b 100644
--- a/src/models/beacon.ts
+++ b/src/models/beacon.ts
@@ -56,7 +56,7 @@ export class Beacon extends TypedEventEmitter<Exclude<BeaconEvent, BeaconEvent.N
     private livenessWatchTimeout?: ReturnType<typeof setTimeout>;
     private _latestLocationEvent?: MatrixEvent;
 
-    constructor(
+    public constructor(
         private rootEvent: MatrixEvent,
     ) {
         super();
@@ -180,7 +180,7 @@ export class Beacon extends TypedEventEmitter<Exclude<BeaconEvent, BeaconEvent.N
         }
     }
 
-    private clearLatestLocation = () => {
+    private clearLatestLocation = (): void => {
         this._latestLocationEvent = undefined;
         this.emit(BeaconEvent.LocationUpdate, this.latestLocationState!);
     };
diff --git a/src/models/event-context.ts b/src/models/event-context.ts
index a1a43e98f..60252627b 100644
--- a/src/models/event-context.ts
+++ b/src/models/event-context.ts
@@ -42,7 +42,7 @@ export class EventContext {
      *
      * @constructor
      */
-    constructor(public readonly ourEvent: MatrixEvent) {
+    public constructor(public readonly ourEvent: MatrixEvent) {
         this.timeline = [ourEvent];
     }
 
diff --git a/src/models/event-timeline-set.ts b/src/models/event-timeline-set.ts
index a69715dc3..6dd2a0e77 100644
--- a/src/models/event-timeline-set.ts
+++ b/src/models/event-timeline-set.ts
@@ -36,7 +36,7 @@ if (DEBUG) {
     // using bind means that we get to keep useful line numbers in the console
     debuglog = logger.log.bind(logger);
 } else {
-    debuglog = function() {};
+    debuglog = function(): void {};
 }
 
 interface IOpts {
@@ -135,7 +135,7 @@ export class EventTimelineSet extends TypedEventEmitter<EmittedEvents, EventTime
      * @param {boolean} isThreadTimeline Whether this timeline set relates to a thread list timeline
      * (e.g., All threads or My threads)
      */
-    constructor(
+    public constructor(
         public readonly room: Room | undefined,
         opts: IOpts = {},
         client?: MatrixClient,
@@ -702,7 +702,7 @@ export class EventTimelineSet extends TypedEventEmitter<EmittedEvents, EventTime
         }
 
         if (timeline.getTimelineSet() !== this) {
-            throw new Error(`EventTimelineSet.addEventToTimeline: Timeline=${timeline.toString()} does not belong " + 
+            throw new Error(`EventTimelineSet.addEventToTimeline: Timeline=${timeline.toString()} does not belong " +
                 "in timelineSet(threadId=${this.thread?.id})`);
         }
 
diff --git a/src/models/event-timeline.ts b/src/models/event-timeline.ts
index a66993812..eff2b7910 100644
--- a/src/models/event-timeline.ts
+++ b/src/models/event-timeline.ts
@@ -67,7 +67,7 @@ export class EventTimeline {
      * @param {RoomState} stateContext  the room state to be queried
      * @param {boolean} toStartOfTimeline  if true the event's forwardLooking flag is set false
      */
-    static setEventMetadata(event: MatrixEvent, stateContext: RoomState, toStartOfTimeline: boolean): void {
+    public static setEventMetadata(event: MatrixEvent, stateContext: RoomState, toStartOfTimeline: boolean): void {
         // When we try to generate a sentinel member before we have that member
         // in the members object, we still generate a sentinel but it doesn't
         // have a membership event, so test to see if events.member is set. We
@@ -130,7 +130,7 @@ export class EventTimeline {
      * @param {EventTimelineSet} eventTimelineSet the set of timelines this is part of
      * @constructor
      */
-    constructor(private readonly eventTimelineSet: EventTimelineSet) {
+    public constructor(private readonly eventTimelineSet: EventTimelineSet) {
         this.roomId = eventTimelineSet.room?.roomId ?? null;
         if (this.roomId) {
             this.startState = new RoomState(this.roomId);
diff --git a/src/models/event.ts b/src/models/event.ts
index e7f38918e..69a63b263 100644
--- a/src/models/event.ts
+++ b/src/models/event.ts
@@ -309,7 +309,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * that getDirectionalContent() will return event.content and not event.prev_content.
      * Default: true. <strong>This property is experimental and may change.</strong>
      */
-    constructor(public event: Partial<IEvent> = {}) {
+    public constructor(public event: Partial<IEvent> = {}) {
         super();
 
         // intern the values of matrix events to force share strings and reduce the
@@ -352,7 +352,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
         return this._cachedExtEv;
     }
 
-    private invalidateExtensibleEvent() {
+    private invalidateExtensibleEvent(): void {
         // just reset the flag - that'll trick the getter into parsing a new event
         this._hasCachedExtEv = false;
     }
@@ -679,7 +679,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
         return this.clearEvent?.content?.msgtype === "m.bad.encrypted";
     }
 
-    public shouldAttemptDecryption() {
+    public shouldAttemptDecryption(): boolean {
         if (this.isRedacted()) return false;
         if (this.isBeingDecrypted()) return false;
         if (this.clearEvent) return false;
@@ -1480,7 +1480,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * more information.
      * @returns {boolean} True if the event is cancelled, false otherwise.
      */
-    isCancelled(): boolean {
+    public isCancelled(): boolean {
         return this._isCancelled;
     }
 
@@ -1498,7 +1498,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * features (such as sender) surrounding the event.
      * @returns {MatrixEvent} A snapshot of this event.
      */
-    toSnapshot(): MatrixEvent {
+    public toSnapshot(): MatrixEvent {
         const ev = new MatrixEvent(JSON.parse(JSON.stringify(this.event)));
         for (const [p, v] of Object.entries(this)) {
             if (p !== "event") { // exclude the thing we just cloned
@@ -1515,7 +1515,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * @param {MatrixEvent} otherEvent The other event to check against.
      * @returns {boolean} True if the events are the same, false otherwise.
      */
-    isEquivalentTo(otherEvent: MatrixEvent): boolean {
+    public isEquivalentTo(otherEvent: MatrixEvent): boolean {
         if (!otherEvent) return false;
         if (otherEvent === this) return true;
         const myProps = deepSortedObjectEntries(this.event);
diff --git a/src/models/invites-ignorer.ts b/src/models/invites-ignorer.ts
index 8a124ede2..ad48fe563 100644
--- a/src/models/invites-ignorer.ts
+++ b/src/models/invites-ignorer.ts
@@ -73,7 +73,7 @@ export enum PolicyScope {
  * our data structures.
  */
 export class IgnoredInvites {
-    constructor(
+    public constructor(
         private readonly client: MatrixClient,
     ) {
     }
@@ -99,7 +99,7 @@ export class IgnoredInvites {
     /**
      * Remove a rule.
      */
-    public async removeRule(event: MatrixEvent) {
+    public async removeRule(event: MatrixEvent): Promise<void> {
         await this.client.redactEvent(event.getRoomId()!, event.getId()!);
     }
 
@@ -314,7 +314,7 @@ export class IgnoredInvites {
     /**
      * Modify in place the `IGNORE_INVITES_POLICIES` object from account data.
      */
-    private async withIgnoreInvitesPolicies(cb: (ignoreInvitesPolicies: {[key: string]: any}) => void) {
+    private async withIgnoreInvitesPolicies(cb: (ignoreInvitesPolicies: {[key: string]: any}) => void): Promise<void> {
         const { policies, ignoreInvitesPolicies } = this.getPoliciesAndIgnoreInvitesPolicies();
         cb(ignoreInvitesPolicies);
         policies[IGNORE_INVITES_ACCOUNT_EVENT_KEY.name] = ignoreInvitesPolicies;
diff --git a/src/models/related-relations.ts b/src/models/related-relations.ts
index 09c618ae8..f619ea059 100644
--- a/src/models/related-relations.ts
+++ b/src/models/related-relations.ts
@@ -29,11 +29,11 @@ export class RelatedRelations {
         return this.relations.reduce<MatrixEvent[]>((c, p) => [...c, ...p.getRelations()], []);
     }
 
-    public on<T extends RelationsEvent>(ev: T, fn: Listener<RelationsEvent, EventHandlerMap, T>) {
+    public on<T extends RelationsEvent>(ev: T, fn: Listener<RelationsEvent, EventHandlerMap, T>): void {
         this.relations.forEach(r => r.on(ev, fn));
     }
 
-    public off<T extends RelationsEvent>(ev: T, fn: Listener<RelationsEvent, EventHandlerMap, T>) {
+    public off<T extends RelationsEvent>(ev: T, fn: Listener<RelationsEvent, EventHandlerMap, T>): void {
         this.relations.forEach(r => r.off(ev, fn));
     }
 }
diff --git a/src/models/relations-container.ts b/src/models/relations-container.ts
index edb261610..55e098a3f 100644
--- a/src/models/relations-container.ts
+++ b/src/models/relations-container.ts
@@ -26,7 +26,7 @@ export class RelationsContainer {
     // this.relations.get(parentEventId).get(relationType).get(relationEventType)
     private relations = new Map<string, Map<RelationType | string, Map<EventType | string, Relations>>>();
 
-    constructor(private readonly client: MatrixClient, private readonly room?: Room) {
+    public constructor(private readonly client: MatrixClient, private readonly room?: Room) {
     }
 
     /**
@@ -98,7 +98,7 @@ export class RelationsContainer {
         const relation = event.getRelation();
         if (!relation) return;
 
-        const onEventDecrypted = () => {
+        const onEventDecrypted = (): void => {
             if (event.isDecryptionFailure()) {
                 // This could for example happen if the encryption keys are not yet available.
                 // The event may still be decrypted later. Register the listener again.
diff --git a/src/models/relations.ts b/src/models/relations.ts
index a384c9b7f..00fb7f6e9 100644
--- a/src/models/relations.ts
+++ b/src/models/relations.ts
@@ -60,7 +60,7 @@ export class Relations extends TypedEventEmitter<RelationsEvent, EventHandlerMap
      * @param {MatrixClient|Room} client
      * The client which created this instance. For backwards compatibility also accepts a Room.
      */
-    constructor(
+    public constructor(
         public readonly relationType: RelationType | string,
         public readonly eventType: string,
         client: MatrixClient | Room,
@@ -75,7 +75,7 @@ export class Relations extends TypedEventEmitter<RelationsEvent, EventHandlerMap
      * @param {MatrixEvent} event
      * The new relation event to be added.
      */
-    public async addEvent(event: MatrixEvent) {
+    public async addEvent(event: MatrixEvent): Promise<void> {
         if (this.relationEventIds.has(event.getId()!)) {
             return;
         }
@@ -123,7 +123,7 @@ export class Relations extends TypedEventEmitter<RelationsEvent, EventHandlerMap
      * @param {MatrixEvent} event
      * The relation event to remove.
      */
-    private async removeEvent(event: MatrixEvent) {
+    private async removeEvent(event: MatrixEvent): Promise<void> {
         if (!this.relations.has(event)) {
             return;
         }
@@ -160,7 +160,7 @@ export class Relations extends TypedEventEmitter<RelationsEvent, EventHandlerMap
      * @param {MatrixEvent} event The event whose status has changed
      * @param {EventStatus} status The new status
      */
-    private onEventStatus = (event: MatrixEvent, status: EventStatus | null) => {
+    private onEventStatus = (event: MatrixEvent, status: EventStatus | null): void => {
         if (!event.isSending()) {
             // Sending is done, so we don't need to listen anymore
             event.removeListener(MatrixEventEvent.Status, this.onEventStatus);
@@ -356,7 +356,7 @@ export class Relations extends TypedEventEmitter<RelationsEvent, EventHandlerMap
     /*
      * @param {MatrixEvent} targetEvent the event the relations are related to.
      */
-    public async setTargetEvent(event: MatrixEvent) {
+    public async setTargetEvent(event: MatrixEvent): Promise<void> {
         if (this.targetEvent) {
             return;
         }
@@ -374,7 +374,7 @@ export class Relations extends TypedEventEmitter<RelationsEvent, EventHandlerMap
         this.maybeEmitCreated();
     }
 
-    private maybeEmitCreated() {
+    private maybeEmitCreated(): void {
         if (this.creationEmitted) {
             return;
         }
diff --git a/src/models/room-member.ts b/src/models/room-member.ts
index 122a55770..28023f791 100644
--- a/src/models/room-member.ts
+++ b/src/models/room-member.ts
@@ -83,7 +83,7 @@ export class RoomMember extends TypedEventEmitter<RoomMemberEvent, RoomMemberEve
      * @prop {MatrixEvent} events.member The m.room.member event for this RoomMember.
      * @prop {boolean} disambiguate True if the member's name is disambiguated.
      */
-    constructor(public readonly roomId: string, public readonly userId: string) {
+    public constructor(public readonly roomId: string, public readonly userId: string) {
         super();
 
         this.name = userId;
@@ -232,7 +232,7 @@ export class RoomMember extends TypedEventEmitter<RoomMemberEvent, RoomMemberEve
     /**
      * Update the last modified time to the current time.
      */
-    private updateModifiedTime() {
+    private updateModifiedTime(): void {
         this.modified = Date.now();
     }
 
diff --git a/src/models/room-state.ts b/src/models/room-state.ts
index 320389cf3..523201d83 100644
--- a/src/models/room-state.ts
+++ b/src/models/room-state.ts
@@ -136,7 +136,7 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
      * events dictionary, keyed on the event type and then the state_key value.
      * @prop {string} paginationToken The pagination token for this state.
      */
-    constructor(public readonly roomId: string, private oobMemberFlags = { status: OobStatus.NotStarted }) {
+    public constructor(public readonly roomId: string, private oobMemberFlags = { status: OobStatus.NotStarted }) {
         super();
         this.updateModifiedTime();
     }
@@ -250,8 +250,8 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
      * <code>undefined</code>, else a single event (or null if no match found).
      */
     public getStateEvents(eventType: EventType | string): MatrixEvent[];
-    public getStateEvents(eventType: EventType | string, stateKey: string): MatrixEvent;
-    public getStateEvents(eventType: EventType | string, stateKey?: string) {
+    public getStateEvents(eventType: EventType | string, stateKey: string): MatrixEvent | null;
+    public getStateEvents(eventType: EventType | string, stateKey?: string): MatrixEvent[] | MatrixEvent | null {
         if (!this.events.has(eventType)) {
             // no match
             return stateKey === undefined ? [] : null;
@@ -342,7 +342,7 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
      * @fires module:client~MatrixClient#event:"RoomState.events"
      * @fires module:client~MatrixClient#event:"RoomStateEvent.Marker"
      */
-    public setStateEvents(stateEvents: MatrixEvent[], markerFoundOptions?: IMarkerFoundOptions) {
+    public setStateEvents(stateEvents: MatrixEvent[], markerFoundOptions?: IMarkerFoundOptions): void {
         this.updateModifiedTime();
 
         // update the core event dict
diff --git a/src/models/room-summary.ts b/src/models/room-summary.ts
index d01b470ae..ba279d2d4 100644
--- a/src/models/room-summary.ts
+++ b/src/models/room-summary.ts
@@ -46,6 +46,6 @@ interface IInfo {
  * @param {Number} info.timestamp The timestamp for this room.
  */
 export class RoomSummary {
-    constructor(public readonly roomId: string, info?: IInfo) {}
+    public constructor(public readonly roomId: string, info?: IInfo) {}
 }
 
diff --git a/src/models/room.ts b/src/models/room.ts
index 21b06a6ce..0d1694027 100644
--- a/src/models/room.ts
+++ b/src/models/room.ts
@@ -317,7 +317,7 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
      * @param {boolean} [opts.timelineSupport = false] Set to true to enable improved
      * timeline support.
      */
-    constructor(
+    public constructor(
         public readonly roomId: string,
         public readonly client: MatrixClient,
         public readonly myUserId: string,
@@ -1950,7 +1950,7 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
         ));
     }
 
-    private updateThreadRootEvents = (thread: Thread, toStartOfTimeline: boolean) => {
+    private updateThreadRootEvents = (thread: Thread, toStartOfTimeline: boolean): void => {
         if (thread.length) {
             this.updateThreadRootEvent(this.threadsTimelineSets?.[0], thread, toStartOfTimeline);
             if (thread.hasCurrentUserParticipated) {
@@ -1963,7 +1963,7 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
         timelineSet: Optional<EventTimelineSet>,
         thread: Thread,
         toStartOfTimeline: boolean,
-    ) => {
+    ): void => {
         if (timelineSet && thread.rootEvent) {
             if (Thread.hasServerSideSupport) {
                 timelineSet.addLiveEvent(thread.rootEvent, {
@@ -2050,7 +2050,7 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
                         redactedEvent.getType(),
                         redactedEvent.getStateKey()!,
                     );
-                    if (currentStateEvent.getId() === redactedEvent.getId()) {
+                    if (currentStateEvent?.getId() === redactedEvent.getId()) {
                         this.currentState.setStateEvents([redactedEvent]);
                     }
                 }
@@ -2913,7 +2913,7 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
         let excludedUserIds: string[] = [];
         const mFunctionalMembers = this.currentState.getStateEvents(UNSTABLE_ELEMENT_FUNCTIONAL_USERS.name, "");
         if (Array.isArray(mFunctionalMembers?.getContent().service_members)) {
-            excludedUserIds = mFunctionalMembers.getContent().service_members;
+            excludedUserIds = mFunctionalMembers!.getContent().service_members;
         }
 
         // get members that are NOT ourselves and are actually in the room.
@@ -3077,7 +3077,7 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
         originalEvent.applyVisibilityEvent(visibilityChange);
     }
 
-    private redactVisibilityChangeEvent(event: MatrixEvent) {
+    private redactVisibilityChangeEvent(event: MatrixEvent): void {
         // Sanity checks.
         if (!event.isVisibilityEvent) {
             throw new Error("expected a visibility change event");
diff --git a/src/models/search-result.ts b/src/models/search-result.ts
index 99f9c5dda..f598301d7 100644
--- a/src/models/search-result.ts
+++ b/src/models/search-result.ts
@@ -60,5 +60,5 @@ export class SearchResult {
      *
      * @constructor
      */
-    constructor(public readonly rank: number, public readonly context: EventContext) {}
+    public constructor(public readonly rank: number, public readonly context: EventContext) {}
 }
diff --git a/src/models/thread.ts b/src/models/thread.ts
index 3c02558bf..5abe63d6c 100644
--- a/src/models/thread.ts
+++ b/src/models/thread.ts
@@ -94,7 +94,7 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
 
     public initialEventsFetched = !Thread.hasServerSideSupport;
 
-    constructor(
+    public constructor(
         public readonly id: string,
         public rootEvent: MatrixEvent | undefined,
         opts: IThreadOpts,
@@ -167,7 +167,7 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
         Thread.hasServerSideFwdPaginationSupport = status;
     }
 
-    private onBeforeRedaction = (event: MatrixEvent, redaction: MatrixEvent) => {
+    private onBeforeRedaction = (event: MatrixEvent, redaction: MatrixEvent): void => {
         if (event?.isRelation(THREAD_RELATION_TYPE.name) &&
             this.room.eventShouldLiveIn(event).threadId === this.id &&
             event.getId() !== this.id && // the root event isn't counted in the length so ignore this redaction
@@ -178,7 +178,7 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
         }
     };
 
-    private onRedaction = async (event: MatrixEvent) => {
+    private onRedaction = async (event: MatrixEvent): Promise<void> => {
         if (event.threadRootId !== this.id) return; // ignore redactions for other timelines
         if (this.replyCount <= 0) {
             for (const threadEvent of this.events) {
@@ -192,7 +192,7 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
         }
     };
 
-    private onEcho = async (event: MatrixEvent) => {
+    private onEcho = async (event: MatrixEvent): Promise<void> => {
         if (event.threadRootId !== this.id) return; // ignore echoes for other timelines
         if (this.lastEvent === event) return;
         if (!event.isRelation(THREAD_RELATION_TYPE.name)) return;
@@ -349,7 +349,7 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
     /**
      * Finds an event by ID in the current thread
      */
-    public findEventById(eventId: string) {
+    public findEventById(eventId: string): MatrixEvent | undefined {
         // Check the lastEvent as it may have been created based on a bundled relationship and not in a timeline
         if (this.lastEvent?.getId() === eventId) {
             return this.lastEvent;
@@ -361,7 +361,7 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
     /**
      * Return last reply to the thread, if known.
      */
-    public lastReply(matches: (ev: MatrixEvent) => boolean = () => true): MatrixEvent | null {
+    public lastReply(matches: (ev: MatrixEvent) => boolean = (): boolean => true): MatrixEvent | null {
         for (let i = this.events.length - 1; i >= 0; i--) {
             const event = this.events[i];
             if (matches(event)) {
diff --git a/src/models/user.ts b/src/models/user.ts
index 31d113dbe..5d92ca494 100644
--- a/src/models/user.ts
+++ b/src/models/user.ts
@@ -76,7 +76,7 @@ export class User extends TypedEventEmitter<UserEvent, UserEventHandlerMap> {
      * @prop {Object} events The events describing this user.
      * @prop {MatrixEvent} events.presence The m.presence event for this user.
      */
-    constructor(public readonly userId: string) {
+    public constructor(public readonly userId: string) {
         super();
         this.displayName = userId;
         this.rawDisplayName = userId;
diff --git a/src/pushprocessor.ts b/src/pushprocessor.ts
index 7c127d4c7..4538b9721 100644
--- a/src/pushprocessor.ts
+++ b/src/pushprocessor.ts
@@ -126,7 +126,7 @@ export class PushProcessor {
      * @constructor
      * @param {Object} client The Matrix client object to use
      */
-    constructor(private readonly client: MatrixClient) {}
+    public constructor(private readonly client: MatrixClient) {}
 
     /**
      * Convert a list of actions into a object with the actions as keys and their values
diff --git a/src/realtime-callbacks.ts b/src/realtime-callbacks.ts
index 222c94763..4677b0c1e 100644
--- a/src/realtime-callbacks.ts
+++ b/src/realtime-callbacks.ts
@@ -48,7 +48,7 @@ type Callback = {
 const callbackList: Callback[] = [];
 
 // var debuglog = logger.log.bind(logger);
-const debuglog = function(...params: any[]) {};
+const debuglog = function(...params: any[]): void {};
 
 /**
  * reimplementation of window.setTimeout, which will call the callback if
diff --git a/src/rendezvous/MSC3906Rendezvous.ts b/src/rendezvous/MSC3906Rendezvous.ts
index c18af5912..a93d4c476 100644
--- a/src/rendezvous/MSC3906Rendezvous.ts
+++ b/src/rendezvous/MSC3906Rendezvous.ts
@@ -143,11 +143,11 @@ export class MSC3906Rendezvous {
         return await this.channel.receive() as MSC3906RendezvousPayload;
     }
 
-    private async send(payload: MSC3906RendezvousPayload) {
+    private async send(payload: MSC3906RendezvousPayload): Promise<void> {
         await this.channel.send(payload);
     }
 
-    public async declineLoginOnExistingDevice() {
+    public async declineLoginOnExistingDevice(): Promise<void> {
         logger.info('User declined sign in');
         await this.send({ type: PayloadType.Finish, outcome: Outcome.Declined });
     }
diff --git a/src/rendezvous/RendezvousError.ts b/src/rendezvous/RendezvousError.ts
index 1c1f6af9c..8b76fc118 100644
--- a/src/rendezvous/RendezvousError.ts
+++ b/src/rendezvous/RendezvousError.ts
@@ -17,7 +17,7 @@ limitations under the License.
 import { RendezvousFailureReason } from ".";
 
 export class RendezvousError extends Error {
-    constructor(message: string, public readonly code: RendezvousFailureReason) {
+    public constructor(message: string, public readonly code: RendezvousFailureReason) {
         super(message);
     }
 }
diff --git a/src/room-hierarchy.ts b/src/room-hierarchy.ts
index 6d95db2a5..c15f2ac56 100644
--- a/src/room-hierarchy.ts
+++ b/src/room-hierarchy.ts
@@ -47,7 +47,7 @@ export class RoomHierarchy {
      * @param {boolean} suggestedOnly whether to only return rooms with suggested=true.
      * @constructor
      */
-    constructor(
+    public constructor(
         public readonly root: Room,
         private readonly pageSize?: number,
         private readonly maxDepth?: number,
diff --git a/src/scheduler.ts b/src/scheduler.ts
index 7a1a99ded..f6d66198a 100644
--- a/src/scheduler.ts
+++ b/src/scheduler.ts
@@ -97,7 +97,7 @@ export class MatrixScheduler<T = ISendEventResponse> {
      * @see module:scheduler~queueAlgorithm
      */
     // eslint-disable-next-line @typescript-eslint/naming-convention
-    public static QUEUE_MESSAGES(event: MatrixEvent) {
+    public static QUEUE_MESSAGES(event: MatrixEvent): "message" | null {
         // enqueue messages or events that associate with another event (redactions and relations)
         if (event.getType() === EventType.RoomMessage || event.hasAssocation()) {
             // put these events in the 'message' queue.
@@ -116,7 +116,7 @@ export class MatrixScheduler<T = ISendEventResponse> {
     private activeQueues: string[] = [];
     private procFn: ProcessFunction<T> | null = null;
 
-    constructor(
+    public constructor(
         public readonly retryAlgorithm = MatrixScheduler.RETRY_BACKOFF_RATELIMIT,
         public readonly queueAlgorithm = MatrixScheduler.QUEUE_MESSAGES,
     ) {}
@@ -283,7 +283,7 @@ export class MatrixScheduler<T = ISendEventResponse> {
     }
 }
 
-function debuglog(...args: any[]) {
+function debuglog(...args: any[]): void {
     if (DEBUG) {
         logger.log(...args);
     }
diff --git a/src/sliding-sync-sdk.ts b/src/sliding-sync-sdk.ts
index 962d824a8..4f3867f54 100644
--- a/src/sliding-sync-sdk.ts
+++ b/src/sliding-sync-sdk.ts
@@ -45,7 +45,7 @@ import { RoomMemberEvent } from "./models/room-member";
 const FAILED_SYNC_ERROR_THRESHOLD = 3;
 
 class ExtensionE2EE implements Extension {
-    constructor(private readonly crypto: Crypto) {}
+    public constructor(private readonly crypto: Crypto) {}
 
     public name(): string {
         return "e2ee";
@@ -95,7 +95,7 @@ class ExtensionE2EE implements Extension {
 class ExtensionToDevice implements Extension {
     private nextBatch: string | null = null;
 
-    constructor(private readonly client: MatrixClient) {}
+    public constructor(private readonly client: MatrixClient) {}
 
     public name(): string {
         return "to_device";
@@ -170,7 +170,7 @@ class ExtensionToDevice implements Extension {
 }
 
 class ExtensionAccountData implements Extension {
-    constructor(private readonly client: MatrixClient) {}
+    public constructor(private readonly client: MatrixClient) {}
 
     public name(): string {
         return "account_data";
@@ -244,7 +244,7 @@ export class SlidingSyncSdk {
     private failCount = 0;
     private notifEvents: MatrixEvent[] = []; // accumulator of sync events in the current sync response
 
-    constructor(
+    public constructor(
         private readonly slidingSync: SlidingSync,
         private readonly client: MatrixClient,
         private readonly opts: Partial<IStoredClientOpts> = {},
@@ -256,7 +256,7 @@ export class SlidingSyncSdk {
         this.opts.experimentalThreadSupport = this.opts.experimentalThreadSupport === true;
 
         if (!opts.canResetEntireTimeline) {
-            opts.canResetEntireTimeline = (_roomId: string) => {
+            opts.canResetEntireTimeline = (_roomId: string): boolean => {
                 return false;
             };
         }
@@ -348,7 +348,7 @@ export class SlidingSyncSdk {
      * Sync rooms the user has left.
      * @return {Promise} Resolved when they've been added to the store.
      */
-    public async syncLeftRooms() {
+    public async syncLeftRooms(): Promise<Room[]> {
         return []; // TODO
     }
 
@@ -457,7 +457,7 @@ export class SlidingSyncSdk {
         return false;
     }
 
-    private async processRoomData(client: MatrixClient, room: Room, roomData: MSC3575RoomData) {
+    private async processRoomData(client: MatrixClient, room: Room, roomData: MSC3575RoomData): Promise<void> {
         roomData = ensureNameEvent(client, room.roomId, roomData);
         const stateEvents = mapEvents(this.client, room.roomId, roomData.required_state);
         // Prevent events from being decrypted ahead of time
@@ -632,7 +632,7 @@ export class SlidingSyncSdk {
         // we'll purge this once we've fully processed the sync response
         this.addNotifications(timelineEvents);
 
-        const processRoomEvent = async (e: MatrixEvent) => {
+        const processRoomEvent = async (e: MatrixEvent): Promise<void> => {
             client.emit(ClientEvent.Event, e);
             if (e.isState() && e.getType() == EventType.RoomEncryption && this.opts.crypto) {
                 await this.opts.crypto.onCryptoEvent(e);
@@ -767,7 +767,7 @@ export class SlidingSyncSdk {
     /**
      * Main entry point. Blocks until stop() is called.
      */
-    public async sync() {
+    public async sync(): Promise<void> {
         logger.debug("Sliding sync init loop");
 
         //   1) We need to get push rules so we can check if events should bing as we get
diff --git a/src/sliding-sync.ts b/src/sliding-sync.ts
index e091c9883..171bf55c3 100644
--- a/src/sliding-sync.ts
+++ b/src/sliding-sync.ts
@@ -169,7 +169,7 @@ class SlidingList {
      * Construct a new sliding list.
      * @param {MSC3575List} list The range, sort and filter values to use for this list.
      */
-    constructor(list: MSC3575List) {
+    public constructor(list: MSC3575List) {
         this.replaceList(list);
     }
 
@@ -373,7 +373,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
      * @param {MatrixClient} client The client to use for /sync calls.
      * @param {number} timeoutMS The number of milliseconds to wait for a response.
      */
-    constructor(
+    public constructor(
         private readonly proxyBaseUrl: string,
         lists: MSC3575List[],
         private roomSubscriptionInfo: MSC3575RoomSubscription,
@@ -391,7 +391,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
      * useCustomSubscription.
      * @param sub The subscription information.
      */
-    public addCustomSubscription(name: string, sub: MSC3575RoomSubscription) {
+    public addCustomSubscription(name: string, sub: MSC3575RoomSubscription): void {
         this.customSubscriptions.set(name, sub);
     }
 
@@ -402,7 +402,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
      * @param name The name of the subscription. If this name is unknown, the default subscription
      * will be used.
      */
-    public useCustomSubscription(roomId: string, name: string) {
+    public useCustomSubscription(roomId: string, name: string): void {
         this.roomIdToCustomSubscription.set(roomId, name);
         // unconfirm this subscription so a resend() will send it up afresh.
         this.confirmedRoomSubscriptions.delete(roomId);
@@ -574,7 +574,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
         this.emit(SlidingSyncEvent.Lifecycle, state, resp, err);
     }
 
-    private shiftRight(listIndex: number, hi: number, low: number) {
+    private shiftRight(listIndex: number, hi: number, low: number): void {
         //     l   h
         // 0,1,2,3,4 <- before
         // 0,1,2,2,3 <- after, hi is deleted and low is duplicated
@@ -588,7 +588,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
         }
     }
 
-    private shiftLeft(listIndex: number, hi: number, low: number) {
+    private shiftLeft(listIndex: number, hi: number, low: number): void {
         //     l   h
         // 0,1,2,3,4 <- before
         // 0,1,3,4,4 <- after, low is deleted and hi is duplicated
@@ -602,7 +602,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
         }
     }
 
-    private removeEntry(listIndex: number, index: number) {
+    private removeEntry(listIndex: number, index: number): void {
         // work out the max index
         let max = -1;
         for (const n in this.lists[listIndex].roomIndexToRoomId) {
@@ -618,7 +618,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
         delete this.lists[listIndex].roomIndexToRoomId[max];
     }
 
-    private addEntry(listIndex: number, index: number) {
+    private addEntry(listIndex: number, index: number): void {
         // work out the max index
         let max = -1;
         for (const n in this.lists[listIndex].roomIndexToRoomId) {
@@ -747,7 +747,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
         return d.promise;
     }
 
-    private resolveTransactionDefers(txnId?: string) {
+    private resolveTransactionDefers(txnId?: string): void {
         if (!txnId) {
             return;
         }
@@ -811,7 +811,7 @@ export class SlidingSync extends TypedEventEmitter<SlidingSyncEvent, SlidingSync
     /**
      * Start syncing with the server. Blocks until stopped.
      */
-    public async start() {
+    public async start(): Promise<void> {
         this.abortController = new AbortController();
 
         let currentPos: string | undefined;
diff --git a/src/store/indexeddb-local-backend.ts b/src/store/indexeddb-local-backend.ts
index 597ed5117..af4b5fc65 100644
--- a/src/store/indexeddb-local-backend.ts
+++ b/src/store/indexeddb-local-backend.ts
@@ -25,7 +25,7 @@ import { IndexedToDeviceBatch, ToDeviceBatchWithTxnId } from "../models/ToDevice
 
 type DbMigration = (db: IDBDatabase) => void;
 const DB_MIGRATIONS: DbMigration[] = [
-    (db) => {
+    (db): void => {
         // Make user store, clobber based on user ID. (userId property of User objects)
         db.createObjectStore("users", { keyPath: ["userId"] });
 
@@ -36,15 +36,15 @@ const DB_MIGRATIONS: DbMigration[] = [
         // Make /sync store (sync tokens, room data, etc), always clobber (const key).
         db.createObjectStore("sync", { keyPath: ["clobber"] });
     },
-    (db) => {
+    (db): void => {
         const oobMembersStore = db.createObjectStore(
             "oob_membership_events", {
                 keyPath: ["room_id", "state_key"],
             });
         oobMembersStore.createIndex("room", "room_id");
     },
-    (db) => { db.createObjectStore("client_options", { keyPath: ["clobber"] }); },
-    (db) => { db.createObjectStore("to_device_queue", { autoIncrement: true }); },
+    (db): void => { db.createObjectStore("client_options", { keyPath: ["clobber"] }); },
+    (db): void => { db.createObjectStore("to_device_queue", { autoIncrement: true }); },
     // Expand as needed.
 ];
 const VERSION = DB_MIGRATIONS.length;
@@ -67,11 +67,11 @@ function selectQuery<T>(
     const query = store.openCursor(keyRange);
     return new Promise((resolve, reject) => {
         const results: T[] = [];
-        query.onerror = () => {
+        query.onerror = (): void => {
             reject(new Error("Query failed: " + query.error));
         };
         // collect results
-        query.onsuccess = () => {
+        query.onsuccess = (): void => {
             const cursor = query.result;
             if (!cursor) {
                 resolve(results);
@@ -85,10 +85,10 @@ function selectQuery<T>(
 
 function txnAsPromise(txn: IDBTransaction): Promise<Event> {
     return new Promise((resolve, reject) => {
-        txn.oncomplete = function(event) {
+        txn.oncomplete = function(event): void {
             resolve(event);
         };
-        txn.onerror = function() {
+        txn.onerror = function(): void {
             reject(txn.error);
         };
     });
@@ -96,10 +96,10 @@ function txnAsPromise(txn: IDBTransaction): Promise<Event> {
 
 function reqAsEventPromise(req: IDBRequest): Promise<Event> {
     return new Promise((resolve, reject) => {
-        req.onsuccess = function(event) {
+        req.onsuccess = function(event): void {
             resolve(event);
         };
-        req.onerror = function() {
+        req.onerror = function(): void {
             reject(req.error);
         };
     });
@@ -107,8 +107,8 @@ function reqAsEventPromise(req: IDBRequest): Promise<Event> {
 
 function reqAsPromise(req: IDBRequest): Promise<IDBRequest> {
     return new Promise((resolve, reject) => {
-        req.onsuccess = () => resolve(req);
-        req.onerror = (err) => reject(err);
+        req.onsuccess = (): void => resolve(req);
+        req.onerror = (err): void => reject(err);
     });
 }
 
@@ -141,7 +141,7 @@ export class LocalIndexedDBStoreBackend implements IIndexedDBBackend {
      * @param {string=} dbName Optional database name. The same name must be used
      * to open the same database.
      */
-    constructor(private readonly indexedDB: IDBFactory, dbName = "default") {
+    public constructor(private readonly indexedDB: IDBFactory, dbName = "default") {
         this.dbName = "matrix-js-sdk:" + dbName;
         this.syncAccumulator = new SyncAccumulator();
     }
@@ -161,7 +161,7 @@ export class LocalIndexedDBStoreBackend implements IIndexedDBBackend {
 
         logger.log(`LocalIndexedDBStoreBackend.connect: connecting...`);
         const req = this.indexedDB.open(this.dbName, VERSION);
-        req.onupgradeneeded = (ev) => {
+        req.onupgradeneeded = (ev): void => {
             const db = req.result;
             const oldVersion = ev.oldVersion;
             logger.log(
@@ -176,22 +176,22 @@ export class LocalIndexedDBStoreBackend implements IIndexedDBBackend {
             });
         };
 
-        req.onblocked = () => {
+        req.onblocked = (): void => {
             logger.log(`can't yet open LocalIndexedDBStoreBackend because it is open elsewhere`);
         };
 
         logger.log(`LocalIndexedDBStoreBackend.connect: awaiting connection...`);
-        return reqAsEventPromise(req).then(() => {
+        return reqAsEventPromise(req).then(async () => {
             logger.log(`LocalIndexedDBStoreBackend.connect: connected`);
             this.db = req.result;
 
             // add a poorly-named listener for when deleteDatabase is called
             // so we can close our db connections.
-            this.db.onversionchange = () => {
+            this.db.onversionchange = (): void => {
                 this.db?.close();
             };
 
-            return this.init();
+            await this.init();
         });
     }
 
@@ -204,7 +204,7 @@ export class LocalIndexedDBStoreBackend implements IIndexedDBBackend {
      * Having connected, load initial data from the database and prepare for use
      * @return {Promise} Resolves on success
      */
-    private init() {
+    private init(): Promise<unknown> {
         return Promise.all([
             this.loadAccountData(),
             this.loadSyncData(),
@@ -243,7 +243,7 @@ export class LocalIndexedDBStoreBackend implements IIndexedDBBackend {
             // were all known already
             let oobWritten = false;
 
-            request.onsuccess = () => {
+            request.onsuccess = (): void => {
                 const cursor = request.result;
                 if (!cursor) {
                     // Unknown room
@@ -260,7 +260,7 @@ export class LocalIndexedDBStoreBackend implements IIndexedDBBackend {
                 }
                 cursor.continue();
             };
-            request.onerror = (err) => {
+            request.onerror = (err): void => {
                 reject(err);
             };
         }).then((events) => {
@@ -346,11 +346,11 @@ export class LocalIndexedDBStoreBackend implements IIndexedDBBackend {
             logger.log(`Removing indexeddb instance: ${this.dbName}`);
             const req = this.indexedDB.deleteDatabase(this.dbName);
 
-            req.onblocked = () => {
+            req.onblocked = (): void => {
                 logger.log(`can't yet delete indexeddb ${this.dbName} because it is open elsewhere`);
             };
 
-            req.onerror = () => {
+            req.onerror = (): void => {
                 // in firefox, with indexedDB disabled, this fails with a
                 // DOMError. We treat this as non-fatal, so that we can still
                 // use the app.
@@ -358,7 +358,7 @@ export class LocalIndexedDBStoreBackend implements IIndexedDBBackend {
                 resolve();
             };
 
-            req.onsuccess = () => {
+            req.onsuccess = (): void => {
                 logger.log(`Removed indexeddb instance: ${this.dbName}`);
                 resolve();
             };
diff --git a/src/store/indexeddb-remote-backend.ts b/src/store/indexeddb-remote-backend.ts
index 39486fe23..1ca6fc03a 100644
--- a/src/store/indexeddb-remote-backend.ts
+++ b/src/store/indexeddb-remote-backend.ts
@@ -42,7 +42,7 @@ export class RemoteIndexedDBStoreBackend implements IIndexedDBBackend {
      * @param {string=} dbName Optional database name. The same name must be used
      * to open the same database.
      */
-    constructor(
+    public constructor(
         private readonly workerFactory: () => Worker,
         private readonly dbName?: string,
     ) {}
diff --git a/src/store/indexeddb-store-worker.ts b/src/store/indexeddb-store-worker.ts
index 691a21f86..57e7da983 100644
--- a/src/store/indexeddb-store-worker.ts
+++ b/src/store/indexeddb-store-worker.ts
@@ -45,7 +45,7 @@ export class IndexedDBStoreWorker {
      * @param {function} postMessage The web worker postMessage function that
      * should be used to communicate back to the main script.
      */
-    constructor(private readonly postMessage: InstanceType<typeof Worker>["postMessage"]) {}
+    public constructor(private readonly postMessage: InstanceType<typeof Worker>["postMessage"]) {}
 
     /**
      * Passes a message event from the main script into the class. This method
diff --git a/src/store/indexeddb.ts b/src/store/indexeddb.ts
index 961e66fd3..55f8261fa 100644
--- a/src/store/indexeddb.ts
+++ b/src/store/indexeddb.ts
@@ -53,7 +53,7 @@ type EventHandlerMap = {
 };
 
 export class IndexedDBStore extends MemoryStore {
-    static exists(indexedDB: IDBFactory, dbName: string): Promise<boolean> {
+    public static exists(indexedDB: IDBFactory, dbName: string): Promise<boolean> {
         return LocalIndexedDBStoreBackend.exists(indexedDB, dbName);
     }
 
@@ -109,7 +109,7 @@ export class IndexedDBStore extends MemoryStore {
      * this API if you need to perform specific indexeddb actions like deleting the
      * database.
      */
-    constructor(opts: IOpts) {
+    public constructor(opts: IOpts) {
         super(opts);
 
         if (!opts.indexedDB) {
diff --git a/src/store/memory.ts b/src/store/memory.ts
index 24b79fccb..f24ab2d97 100644
--- a/src/store/memory.ts
+++ b/src/store/memory.ts
@@ -69,7 +69,7 @@ export class MemoryStore implements IStore {
     private pendingToDeviceBatches: IndexedToDeviceBatch[] = [];
     private nextToDeviceBatchId = 0;
 
-    constructor(opts: IOpts = {}) {
+    public constructor(opts: IOpts = {}) {
         this.localStorage = opts.localStorage;
     }
 
@@ -90,7 +90,7 @@ export class MemoryStore implements IStore {
      * Set the token to stream from.
      * @param {string} token The token to stream from.
      */
-    public setSyncToken(token: string) {
+    public setSyncToken(token: string): void {
         this.syncToken = token;
     }
 
@@ -98,7 +98,7 @@ export class MemoryStore implements IStore {
      * Store the given room.
      * @param {Room} room The room to be stored. All properties must be stored.
      */
-    public storeRoom(room: Room) {
+    public storeRoom(room: Room): void {
         this.rooms[room.roomId] = room;
         // add listeners for room member changes so we can keep the room member
         // map up-to-date.
@@ -116,7 +116,7 @@ export class MemoryStore implements IStore {
      * @param {RoomState} state
      * @param {RoomMember} member
      */
-    private onRoomMember = (event: MatrixEvent | null, state: RoomState, member: RoomMember) => {
+    private onRoomMember = (event: MatrixEvent | null, state: RoomState, member: RoomMember): void => {
         if (member.membership === "invite") {
             // We do NOT add invited members because people love to typo user IDs
             // which would then show up in these lists (!)
@@ -217,7 +217,7 @@ export class MemoryStore implements IStore {
      * @param {string} token The token associated with these events.
      * @param {boolean} toStart True if these are paginated results.
      */
-    public storeEvents(room: Room, events: MatrixEvent[], token: string, toStart: boolean) {
+    public storeEvents(room: Room, events: MatrixEvent[], token: string, toStart: boolean): void {
         // no-op because they've already been added to the room instance.
     }
 
@@ -275,7 +275,7 @@ export class MemoryStore implements IStore {
      * @param {string} filterName
      * @param {string} filterId
      */
-    public setFilterIdByName(filterName: string, filterId?: string) {
+    public setFilterIdByName(filterName: string, filterId?: string): void {
         if (!this.localStorage) {
             return;
         }
diff --git a/src/store/stub.ts b/src/store/stub.ts
index 64a35d513..746bc521f 100644
--- a/src/store/stub.ts
+++ b/src/store/stub.ts
@@ -56,7 +56,7 @@ export class StubStore implements IStore {
      * Set the sync token.
      * @param {string} token
      */
-    public setSyncToken(token: string) {
+    public setSyncToken(token: string): void {
         this.fromToken = token;
     }
 
@@ -64,7 +64,7 @@ export class StubStore implements IStore {
      * No-op.
      * @param {Room} room
      */
-    public storeRoom(room: Room) {}
+    public storeRoom(room: Room): void {}
 
     /**
      * No-op.
@@ -87,7 +87,7 @@ export class StubStore implements IStore {
      * Permanently delete a room.
      * @param {string} roomId
      */
-    public removeRoom(roomId: string) {
+    public removeRoom(roomId: string): void {
         return;
     }
 
@@ -103,7 +103,7 @@ export class StubStore implements IStore {
      * No-op.
      * @param {User} user
      */
-    public storeUser(user: User) {}
+    public storeUser(user: User): void {}
 
     /**
      * No-op.
@@ -139,13 +139,13 @@ export class StubStore implements IStore {
      * @param {string} token The token associated with these events.
      * @param {boolean} toStart True if these are paginated results.
      */
-    public storeEvents(room: Room, events: MatrixEvent[], token: string, toStart: boolean) {}
+    public storeEvents(room: Room, events: MatrixEvent[], token: string, toStart: boolean): void {}
 
     /**
      * Store a filter.
      * @param {Filter} filter
      */
-    public storeFilter(filter: Filter) {}
+    public storeFilter(filter: Filter): void {}
 
     /**
      * Retrieve a filter.
@@ -171,13 +171,13 @@ export class StubStore implements IStore {
      * @param {string} filterName
      * @param {string} filterId
      */
-    public setFilterIdByName(filterName: string, filterId?: string) {}
+    public setFilterIdByName(filterName: string, filterId?: string): void {}
 
     /**
      * Store user-scoped account data events
      * @param {Array<MatrixEvent>} events The events to store.
      */
-    public storeAccountDataEvents(events: MatrixEvent[]) {}
+    public storeAccountDataEvents(events: MatrixEvent[]): void {}
 
     /**
      * Get account data event by event type
@@ -209,7 +209,7 @@ export class StubStore implements IStore {
     /**
      * Save does nothing as there is no backing data store.
      */
-    public save() {}
+    public save(): void {}
 
     /**
      * Startup does nothing.
diff --git a/src/sync-accumulator.ts b/src/sync-accumulator.ts
index 484e96e4f..19d5cf131 100644
--- a/src/sync-accumulator.ts
+++ b/src/sync-accumulator.ts
@@ -211,7 +211,7 @@ export class SyncAccumulator {
      * never be more. This cannot be 0 or else it makes it impossible to scroll
      * back in a room. Default: 50.
      */
-    constructor(private readonly opts: IOpts = {}) {
+    public constructor(private readonly opts: IOpts = {}) {
         this.opts.maxTimelineEntries = this.opts.maxTimelineEntries || 50;
     }
 
diff --git a/src/sync.ts b/src/sync.ts
index d85bfc4cb..f32ccf7d2 100644
--- a/src/sync.ts
+++ b/src/sync.ts
@@ -106,7 +106,7 @@ function getFilterName(userId: string, suffix?: string): string {
     return `FILTER_SYNC_${userId}` + (suffix ? "_" + suffix : "");
 }
 
-function debuglog(...params) {
+function debuglog(...params): void {
     if (!DEBUG) return;
     logger.log(...params);
 }
@@ -175,7 +175,7 @@ export class SyncApi {
     private failedSyncCount = 0; // Number of consecutive failed /sync requests
     private storeIsInvalid = false; // flag set if the store needs to be cleared before we can start
 
-    constructor(private readonly client: MatrixClient, private readonly opts: Partial<IStoredClientOpts> = {}) {
+    public constructor(private readonly client: MatrixClient, private readonly opts: Partial<IStoredClientOpts> = {}) {
         this.opts.initialSyncLimit = this.opts.initialSyncLimit ?? 8;
         this.opts.resolveInvitesToProfiles = this.opts.resolveInvitesToProfiles || false;
         this.opts.pollTimeout = this.opts.pollTimeout || (30 * 1000);
@@ -183,7 +183,7 @@ export class SyncApi {
         this.opts.experimentalThreadSupport = this.opts.experimentalThreadSupport === true;
 
         if (!opts.canResetEntireTimeline) {
-            opts.canResetEntireTimeline = (roomId: string) => {
+            opts.canResetEntireTimeline = (roomId: string): boolean => {
                 return false;
             };
         }
@@ -554,7 +554,7 @@ export class SyncApi {
         return false;
     }
 
-    private getPushRules = async () => {
+    private getPushRules = async (): Promise<void> => {
         try {
             debuglog("Getting push rules...");
             const result = await this.client.getPushRules();
@@ -572,7 +572,7 @@ export class SyncApi {
         }
     };
 
-    private buildDefaultFilter = () => {
+    private buildDefaultFilter = (): Filter => {
         const filter = new Filter(this.client.credentials.userId);
         if (this.client.canSupport.get(Feature.ThreadUnreadNotifications) !== ServerSupport.Unsupported) {
             filter.setUnreadThreadNotifications(true);
@@ -580,7 +580,7 @@ export class SyncApi {
         return filter;
     };
 
-    private checkLazyLoadStatus = async () => {
+    private checkLazyLoadStatus = async (): Promise<void> => {
         debuglog("Checking lazy load status...");
         if (this.opts.lazyLoadMembers && this.client.isGuest()) {
             this.opts.lazyLoadMembers = false;
@@ -1389,7 +1389,7 @@ export class SyncApi {
 
             this.processEventsForNotifs(room, events);
 
-            const processRoomEvent = async (e) => {
+            const processRoomEvent = async (e): Promise<void> => {
                 client.emit(ClientEvent.Event, e);
                 if (e.isState() && e.getType() == "m.room.encryption" && this.opts.crypto) {
                     await this.opts.crypto.onCryptoEvent(e);
@@ -1521,7 +1521,7 @@ export class SyncApi {
      * @param {boolean} connDidFail True if a connectivity failure has been detected. Optional.
      */
     private pokeKeepAlive(connDidFail = false): void {
-        const success = () => {
+        const success = (): void => {
             clearTimeout(this.keepAliveTimer);
             if (this.connectionReturnedDefer) {
                 this.connectionReturnedDefer.resolve(connDidFail);
diff --git a/src/timeline-window.ts b/src/timeline-window.ts
index c5560bdf4..5498600a9 100644
--- a/src/timeline-window.ts
+++ b/src/timeline-window.ts
@@ -32,7 +32,7 @@ const DEBUG = false;
 /**
  * @private
  */
-const debuglog = DEBUG ? logger.log.bind(logger) : function() {};
+const debuglog = DEBUG ? logger.log.bind(logger) : function(): void {};
 
 /**
  * the number of times we ask the server for more events before giving up
@@ -84,7 +84,7 @@ export class TimelineWindow {
      *
      * @constructor
      */
-    constructor(
+    public constructor(
         private readonly client: MatrixClient,
         private readonly timelineSet: EventTimelineSet,
         opts: IOpts = {},
@@ -104,7 +104,7 @@ export class TimelineWindow {
     public load(initialEventId?: string, initialWindowSize = 20): Promise<void> {
         // given an EventTimeline, find the event we were looking for, and initialise our
         // fields so that the event in question is in the middle of the window.
-        const initFields = (timeline: Optional<EventTimeline>) => {
+        const initFields = (timeline: Optional<EventTimeline>): void => {
             if (!timeline) {
                 throw new Error("No timeline given to initFields");
             }
@@ -430,7 +430,7 @@ export class TimelineIndex {
     public pendingPaginate?: Promise<boolean>;
 
     // index: the indexes are relative to BaseIndex, so could well be negative.
-    constructor(public timeline: EventTimeline, public index: number) {}
+    public constructor(public timeline: EventTimeline, public index: number) {}
 
     /**
      * @return {number} the minimum possible value for the index in the current
diff --git a/src/utils.ts b/src/utils.ts
index d4364f18a..201be5b3e 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -178,7 +178,7 @@ export function removeElement<T>(
  * @param {*} value The thing to check.
  * @return {boolean} True if it is a function.
  */
-export function isFunction(value: any) {
+export function isFunction(value: any): boolean {
     return Object.prototype.toString.call(value) === "[object Function]";
 }
 
@@ -189,7 +189,7 @@ export function isFunction(value: any) {
  * @throws If the object is missing keys.
  */
 // note using 'keys' here would shadow the 'keys' function defined above
-export function checkObjectHasKeys(obj: object, keys: string[]) {
+export function checkObjectHasKeys(obj: object, keys: string[]): void {
     for (const key of keys) {
         if (!obj.hasOwnProperty(key)) {
             throw new Error("Missing required key: " + key);
@@ -383,7 +383,7 @@ export function globToRegexp(glob: string, extended = false): string {
     if (!extended) {
         replacements.push([
             /\\\[(!|)(.*)\\]/g,
-            (_match: string, neg: string, pat: string) => [
+            (_match: string, neg: string, pat: string): string => [
                 '[',
                 neg ? '^' : '',
                 pat.replace(/\\-/, '-'),
@@ -490,7 +490,7 @@ export function simpleRetryOperation<T>(promiseFn: (attempt: number) => Promise<
  * The default alphabet used by string averaging in this SDK. This matches
  * all usefully printable ASCII characters (0x20-0x7E, inclusive).
  */
-export const DEFAULT_ALPHABET = (() => {
+export const DEFAULT_ALPHABET = ((): string => {
     let str = "";
     for (let c = 0x20; c <= 0x7E; c++) {
         str += String.fromCharCode(c);
diff --git a/src/webrtc/audioContext.ts b/src/webrtc/audioContext.ts
index 8a9ceb15d..0e08574b8 100644
--- a/src/webrtc/audioContext.ts
+++ b/src/webrtc/audioContext.ts
@@ -35,7 +35,7 @@ export const acquireContext = (): AudioContext => {
  * released, allowing the context and associated hardware resources to be
  * cleaned up if nothing else is using it.
  */
-export const releaseContext = () => {
+export const releaseContext = (): void => {
     refCount--;
     if (refCount === 0) {
         audioContext?.close();
diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 22a6d8ec1..0e4a664fb 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -268,7 +268,7 @@ const CALL_TIMEOUT_MS = 60000;
 export class CallError extends Error {
     public readonly code: string;
 
-    constructor(code: CallErrorCode, msg: string, err: Error) {
+    public constructor(code: CallErrorCode, msg: string, err: Error) {
         // Still don't think there's any way to have proper nested errors
         super(msg + ": " + err);
 
@@ -404,7 +404,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
     private opponentSessionId?: string;
     public groupCallId?: string;
 
-    constructor(opts: CallOpts) {
+    public constructor(opts: CallOpts) {
         super();
 
         this.roomId = opts.roomId;
@@ -452,7 +452,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
      * @param label A human readable label for this datachannel
      * @param options An object providing configuration options for the data channel.
      */
-    public createDataChannel(label: string, options: RTCDataChannelInit | undefined) {
+    public createDataChannel(label: string, options: RTCDataChannelInit | undefined): RTCDataChannel {
         const dataChannel = this.peerConn!.createDataChannel(label, options);
         this.emit(CallEvent.DataChannel, dataChannel);
         return dataChannel;
@@ -564,7 +564,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         return this.feeds.filter((feed) => !feed.isLocal());
     }
 
-    private async initOpponentCrypto() {
+    private async initOpponentCrypto(): Promise<void> {
         if (!this.opponentDeviceId) return;
         if (!this.client.getUseE2eForGroupCall()) return;
         // It's possible to want E2EE and yet not have the means to manage E2EE
@@ -938,7 +938,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
                 }
             }, invite.lifetime - event.getLocalAge());
 
-            const onState = (state: CallState) => {
+            const onState = (state: CallState): void => {
                 if (state !== CallState.Ringing) {
                     clearTimeout(ringingTimer);
                     this.off(CallEvent.State, onState);
@@ -2132,7 +2132,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         this.pushRemoteFeed(stream);
 
         if (!this.removeTrackListeners.has(stream)) {
-            const onRemoveTrack = () => {
+            const onRemoveTrack = (): void => {
                 if (stream.getTracks().length === 0) {
                     logger.info(`Call ${this.callId} removing track streamId: ${stream.id}`);
                     this.deleteFeedByStream(stream);
diff --git a/src/webrtc/callEventHandler.ts b/src/webrtc/callEventHandler.ts
index c4c48cf50..7cbefd46e 100644
--- a/src/webrtc/callEventHandler.ts
+++ b/src/webrtc/callEventHandler.ts
@@ -46,7 +46,7 @@ export class CallEventHandler {
     private candidateEventsByCall: Map<string, Array<MatrixEvent>>;
     private eventBufferPromiseChain?: Promise<void>;
 
-    constructor(client: MatrixClient) {
+    public constructor(client: MatrixClient) {
         this.client = client;
         this.calls = new Map<string, MatrixCall>();
         // The sync code always emits one event at a time, so it will patiently
@@ -61,13 +61,13 @@ export class CallEventHandler {
         this.candidateEventsByCall = new Map<string, Array<MatrixEvent>>();
     }
 
-    public start() {
+    public start(): void {
         this.client.on(ClientEvent.Sync, this.onSync);
         this.client.on(RoomEvent.Timeline, this.onRoomTimeline);
         this.client.on(ClientEvent.ToDeviceEvent, this.onToDeviceEvent);
     }
 
-    public stop() {
+    public stop(): void {
         this.client.removeListener(ClientEvent.Sync, this.onSync);
         this.client.removeListener(RoomEvent.Timeline, this.onRoomTimeline);
         this.client.removeListener(ClientEvent.ToDeviceEvent, this.onToDeviceEvent);
@@ -87,7 +87,7 @@ export class CallEventHandler {
         }
     };
 
-    private async evaluateEventBuffer(eventBuffer: MatrixEvent[]) {
+    private async evaluateEventBuffer(eventBuffer: MatrixEvent[]): Promise<void> {
         await Promise.all(eventBuffer.map((event) => this.client.decryptEventIfNeeded(event)));
 
         const callEvents = eventBuffer.filter((event) => {
@@ -125,7 +125,7 @@ export class CallEventHandler {
         }
     }
 
-    private onRoomTimeline = (event: MatrixEvent) => {
+    private onRoomTimeline = (event: MatrixEvent): void => {
         this.callEventBuffer.push(event);
     };
 
@@ -178,7 +178,7 @@ export class CallEventHandler {
         }
     };
 
-    private async handleCallEvent(event: MatrixEvent) {
+    private async handleCallEvent(event: MatrixEvent): Promise<void> {
         this.client.emit(ClientEvent.ReceivedVoipEvent, event);
 
         const content = event.getContent();
diff --git a/src/webrtc/callFeed.ts b/src/webrtc/callFeed.ts
index 965a04441..6f71b5040 100644
--- a/src/webrtc/callFeed.ts
+++ b/src/webrtc/callFeed.ts
@@ -80,7 +80,7 @@ export class CallFeed extends TypedEventEmitter<CallFeedEvent, EventHandlerMap>
     private volumeLooperTimeout?: ReturnType<typeof setTimeout>;
     private _disposed = false;
 
-    constructor(opts: ICallFeedOpts) {
+    public constructor(opts: ICallFeedOpts) {
         super();
 
         this.client = opts.client;
@@ -227,11 +227,11 @@ export class CallFeed extends TypedEventEmitter<CallFeedEvent, EventHandlerMap>
         }
     }
 
-    public setSpeakingThreshold(threshold: number) {
+    public setSpeakingThreshold(threshold: number): void {
         this.speakingThreshold = threshold;
     }
 
-    private volumeLooper = () => {
+    private volumeLooper = (): void => {
         if (!this.analyser) return;
 
         if (!this.measuringVolumeActivity) return;
diff --git a/src/webrtc/groupCall.ts b/src/webrtc/groupCall.ts
index 737528253..cafcadb10 100644
--- a/src/webrtc/groupCall.ts
+++ b/src/webrtc/groupCall.ts
@@ -73,7 +73,7 @@ export enum GroupCallErrorCode {
 export class GroupCallError extends Error {
     public code: string;
 
-    constructor(code: GroupCallErrorCode, msg: string, err?: Error) {
+    public constructor(code: GroupCallErrorCode, msg: string, err?: Error) {
         // Still don't think there's any way to have proper nested errors
         if (err) {
             super(msg + ": " + err);
@@ -86,13 +86,13 @@ export class GroupCallError extends Error {
 }
 
 export class GroupCallUnknownDeviceError extends GroupCallError {
-    constructor(public userId: string) {
+    public constructor(public userId: string) {
         super(GroupCallErrorCode.UnknownDevice, "No device found for " + userId);
     }
 }
 
 export class OtherUserSpeakingError extends Error {
-    constructor() {
+    public constructor() {
         super("Cannot unmute: another user is speaking");
     }
 }
@@ -187,7 +187,7 @@ export class GroupCall extends TypedEventEmitter<
     private initWithAudioMuted = false;
     private initWithVideoMuted = false;
 
-    constructor(
+    public constructor(
         private client: MatrixClient,
         public room: Room,
         public type: GroupCallType,
@@ -206,7 +206,7 @@ export class GroupCall extends TypedEventEmitter<
         }
     }
 
-    public async create() {
+    public async create(): Promise<GroupCall> {
         this.client.groupCallEventHandler!.groupCalls.set(this.room.roomId, this);
 
         await this.client.sendStateEvent(
@@ -258,7 +258,7 @@ export class GroupCall extends TypedEventEmitter<
         let stream: MediaStream;
 
         let disposed = false;
-        const onState = (state: GroupCallState) => {
+        const onState = (state: GroupCallState): void => {
             if (state === GroupCallState.LocalCallFeedUninitialized) {
                 disposed = true;
             }
@@ -300,7 +300,7 @@ export class GroupCall extends TypedEventEmitter<
         return callFeed;
     }
 
-    public async updateLocalUsermediaStream(stream: MediaStream) {
+    public async updateLocalUsermediaStream(stream: MediaStream): Promise<void> {
         if (this.localCallFeed) {
             const oldStream = this.localCallFeed.stream;
             this.localCallFeed.setNewStream(stream);
@@ -315,7 +315,7 @@ export class GroupCall extends TypedEventEmitter<
         }
     }
 
-    public async enter() {
+    public async enter(): Promise<void> {
         if (!(this.state === GroupCallState.LocalCallFeedUninitialized ||
             this.state === GroupCallState.LocalCallFeedInitialized)) {
             throw new Error(`Cannot enter call in the "${this.state}" state`);
@@ -354,7 +354,7 @@ export class GroupCall extends TypedEventEmitter<
         this.onActiveSpeakerLoop();
     }
 
-    private dispose() {
+    private dispose(): void {
         if (this.localCallFeed) {
             this.removeUserMediaFeed(this.localCallFeed);
             this.localCallFeed = undefined;
@@ -400,7 +400,7 @@ export class GroupCall extends TypedEventEmitter<
         this.client.removeListener(CallEventHandlerEvent.Incoming, this.onIncomingCall);
     }
 
-    public leave() {
+    public leave(): void {
         if (this.transmitTimer !== null) {
             clearTimeout(this.transmitTimer);
             this.transmitTimer = null;
@@ -410,7 +410,7 @@ export class GroupCall extends TypedEventEmitter<
         this.setState(GroupCallState.LocalCallFeedUninitialized);
     }
 
-    public async terminate(emitStateEvent = true) {
+    public async terminate(emitStateEvent = true): Promise<void> {
         this.dispose();
 
         if (this.transmitTimer !== null) {
@@ -430,7 +430,7 @@ export class GroupCall extends TypedEventEmitter<
                 this.room.roomId,
                 EventType.GroupCallPrefix,
                 {
-                    ...existingStateEvent.getContent(),
+                    ...existingStateEvent!.getContent(),
                     ["m.terminated"]: GroupCallTerminationReason.CallEnded,
                 },
                 this.groupCallId,
@@ -445,7 +445,7 @@ export class GroupCall extends TypedEventEmitter<
      * Local Usermedia
      */
 
-    public isLocalVideoMuted() {
+    public isLocalVideoMuted(): boolean {
         if (this.localCallFeed) {
             return this.localCallFeed.isVideoMuted();
         }
@@ -453,7 +453,7 @@ export class GroupCall extends TypedEventEmitter<
         return true;
     }
 
-    public isMicrophoneMuted() {
+    public isMicrophoneMuted(): boolean {
         if (this.localCallFeed) {
             return this.localCallFeed.isAudioMuted();
         }
@@ -576,7 +576,7 @@ export class GroupCall extends TypedEventEmitter<
                 const stream = await this.client.getMediaHandler().getScreensharingStream(opts);
 
                 for (const track of stream.getTracks()) {
-                    const onTrackEnded = () => {
+                    const onTrackEnded = (): void => {
                         this.setScreensharingEnabled(false);
                         track.removeEventListener("ended", onTrackEnded);
                     };
@@ -651,7 +651,7 @@ export class GroupCall extends TypedEventEmitter<
      *    as they are observed by the RoomState.members event.
      */
 
-    private onIncomingCall = (newCall: MatrixCall) => {
+    private onIncomingCall = (newCall: MatrixCall): void => {
         // The incoming calls may be for another room, which we will ignore.
         if (newCall.roomId !== this.room.roomId) {
             return;
@@ -700,7 +700,7 @@ export class GroupCall extends TypedEventEmitter<
     private getMemberStateEvents(userId?: string): MatrixEvent[] | MatrixEvent | null {
         if (userId != null) {
             const event = this.room.currentState.getStateEvents(EventType.GroupCallMemberPrefix, userId);
-            return callMemberStateIsExpired(event) ? null : event;
+            return callMemberStateIsExpired(event!) ? null : event;
         } else {
             return this.room.currentState.getStateEvents(EventType.GroupCallMemberPrefix)
                 .filter(event => !callMemberStateIsExpired(event));
@@ -708,7 +708,7 @@ export class GroupCall extends TypedEventEmitter<
     }
 
     private async sendMemberStateEvent(): Promise<ISendEventResponse> {
-        const send = () => this.updateMemberCallState({
+        const send = (): Promise<ISendEventResponse> => this.updateMemberCallState({
             "m.call_id": this.groupCallId,
             "m.devices": [
                 {
@@ -779,7 +779,7 @@ export class GroupCall extends TypedEventEmitter<
         );
     }
 
-    public onMemberStateChanged = async (event: MatrixEvent) => {
+    public onMemberStateChanged = async (event: MatrixEvent): Promise<void> => {
         // If we haven't entered the call yet, we don't care
         if (this.state !== GroupCallState.Entered) {
             return;
@@ -800,7 +800,7 @@ export class GroupCall extends TypedEventEmitter<
 
         logger.debug(`Processing member state event for ${member.userId}`);
 
-        const ignore = () => {
+        const ignore = (): void => {
             this.removeParticipant(member);
             clearTimeout(this.memberStateExpirationTimers.get(member.userId));
             this.memberStateExpirationTimers.delete(member.userId);
@@ -953,7 +953,7 @@ export class GroupCall extends TypedEventEmitter<
         return memberDevices[0];
     }
 
-    private onRetryCallLoop = () => {
+    private onRetryCallLoop = (): void => {
         for (const event of this.getMemberStateEvents()) {
             const memberId = event.getStateKey()!;
             const existingCall = this.calls.find((call) => getCallUserId(call) === memberId);
@@ -976,13 +976,17 @@ export class GroupCall extends TypedEventEmitter<
         return this.calls.find((call) => getCallUserId(call) === userId);
     }
 
-    private addCall(call: MatrixCall) {
+    private addCall(call: MatrixCall): void {
         this.calls.push(call);
         this.initCall(call);
         this.emit(GroupCallEvent.CallsChanged, this.calls);
     }
 
-    private replaceCall(existingCall: MatrixCall, replacementCall: MatrixCall, hangupReason = CallErrorCode.Replaced) {
+    private replaceCall(
+        existingCall: MatrixCall,
+        replacementCall: MatrixCall,
+        hangupReason = CallErrorCode.Replaced,
+    ): void {
         const existingCallIndex = this.calls.indexOf(existingCall);
 
         if (existingCallIndex === -1) {
@@ -997,7 +1001,7 @@ export class GroupCall extends TypedEventEmitter<
         this.emit(GroupCallEvent.CallsChanged, this.calls);
     }
 
-    private removeCall(call: MatrixCall, hangupReason: CallErrorCode) {
+    private removeCall(call: MatrixCall, hangupReason: CallErrorCode): void {
         this.disposeCall(call, hangupReason);
 
         const callIndex = this.calls.indexOf(call);
@@ -1011,18 +1015,20 @@ export class GroupCall extends TypedEventEmitter<
         this.emit(GroupCallEvent.CallsChanged, this.calls);
     }
 
-    private initCall(call: MatrixCall) {
+    private initCall(call: MatrixCall): void {
         const opponentMemberId = getCallUserId(call);
 
         if (!opponentMemberId) {
             throw new Error("Cannot init call without user id");
         }
 
-        const onCallFeedsChanged = () => this.onCallFeedsChanged(call);
-        const onCallStateChanged =
-            (state: CallState, oldState: CallState | undefined) => this.onCallStateChanged(call, state, oldState);
+        const onCallFeedsChanged = (): void => this.onCallFeedsChanged(call);
+        const onCallStateChanged = (
+            state: CallState,
+            oldState?: CallState,
+        ): void => this.onCallStateChanged(call, state, oldState);
         const onCallHangup = this.onCallHangup;
-        const onCallReplaced = (newCall: MatrixCall) => this.replaceCall(call, newCall);
+        const onCallReplaced = (newCall: MatrixCall): void => this.replaceCall(call, newCall);
 
         this.callHandlers.set(opponentMemberId, {
             onCallFeedsChanged,
@@ -1041,7 +1047,7 @@ export class GroupCall extends TypedEventEmitter<
         onCallFeedsChanged();
     }
 
-    private disposeCall(call: MatrixCall, hangupReason: CallErrorCode) {
+    private disposeCall(call: MatrixCall, hangupReason: CallErrorCode): void {
         const opponentMemberId = getCallUserId(call);
 
         if (!opponentMemberId) {
@@ -1083,7 +1089,7 @@ export class GroupCall extends TypedEventEmitter<
         }
     }
 
-    private onCallFeedsChanged = (call: MatrixCall) => {
+    private onCallFeedsChanged = (call: MatrixCall): void => {
         const opponentMemberId = getCallUserId(call);
 
         if (!opponentMemberId) {
@@ -1119,7 +1125,7 @@ export class GroupCall extends TypedEventEmitter<
         }
     };
 
-    private onCallStateChanged = (call: MatrixCall, state: CallState, _oldState: CallState | undefined) => {
+    private onCallStateChanged = (call: MatrixCall, state: CallState, _oldState: CallState | undefined): void => {
         const audioMuted = this.localCallFeed!.isAudioMuted();
 
         if (
@@ -1143,7 +1149,7 @@ export class GroupCall extends TypedEventEmitter<
         }
     };
 
-    private onCallHangup = (call: MatrixCall) => {
+    private onCallHangup = (call: MatrixCall): void => {
         if (call.hangupReason === CallErrorCode.Replaced) {
             return;
         }
@@ -1155,17 +1161,17 @@ export class GroupCall extends TypedEventEmitter<
      * UserMedia CallFeed Event Handlers
      */
 
-    public getUserMediaFeedByUserId(userId: string) {
+    public getUserMediaFeedByUserId(userId: string): CallFeed | undefined {
         return this.userMediaFeeds.find((feed) => feed.userId === userId);
     }
 
-    private addUserMediaFeed(callFeed: CallFeed) {
+    private addUserMediaFeed(callFeed: CallFeed): void {
         this.userMediaFeeds.push(callFeed);
         callFeed.measureVolumeActivity(true);
         this.emit(GroupCallEvent.UserMediaFeedsChanged, this.userMediaFeeds);
     }
 
-    private replaceUserMediaFeed(existingFeed: CallFeed, replacementFeed: CallFeed) {
+    private replaceUserMediaFeed(existingFeed: CallFeed, replacementFeed: CallFeed): void {
         const feedIndex = this.userMediaFeeds.findIndex((feed) => feed.userId === existingFeed.userId);
 
         if (feedIndex === -1) {
@@ -1179,7 +1185,7 @@ export class GroupCall extends TypedEventEmitter<
         this.emit(GroupCallEvent.UserMediaFeedsChanged, this.userMediaFeeds);
     }
 
-    private removeUserMediaFeed(callFeed: CallFeed) {
+    private removeUserMediaFeed(callFeed: CallFeed): void {
         const feedIndex = this.userMediaFeeds.findIndex((feed) => feed.userId === callFeed.userId);
 
         if (feedIndex === -1) {
@@ -1200,7 +1206,7 @@ export class GroupCall extends TypedEventEmitter<
         }
     }
 
-    private onActiveSpeakerLoop = () => {
+    private onActiveSpeakerLoop = (): void => {
         let topAvg: number | undefined = undefined;
         let nextActiveSpeaker: string | undefined = undefined;
 
@@ -1239,16 +1245,16 @@ export class GroupCall extends TypedEventEmitter<
      * Screenshare Call Feed Event Handlers
      */
 
-    public getScreenshareFeedByUserId(userId: string) {
+    public getScreenshareFeedByUserId(userId: string): CallFeed | undefined {
         return this.screenshareFeeds.find((feed) => feed.userId === userId);
     }
 
-    private addScreenshareFeed(callFeed: CallFeed) {
+    private addScreenshareFeed(callFeed: CallFeed): void {
         this.screenshareFeeds.push(callFeed);
         this.emit(GroupCallEvent.ScreenshareFeedsChanged, this.screenshareFeeds);
     }
 
-    private replaceScreenshareFeed(existingFeed: CallFeed, replacementFeed: CallFeed) {
+    private replaceScreenshareFeed(existingFeed: CallFeed, replacementFeed: CallFeed): void {
         const feedIndex = this.screenshareFeeds.findIndex((feed) => feed.userId === existingFeed.userId);
 
         if (feedIndex === -1) {
@@ -1261,7 +1267,7 @@ export class GroupCall extends TypedEventEmitter<
         this.emit(GroupCallEvent.ScreenshareFeedsChanged, this.screenshareFeeds);
     }
 
-    private removeScreenshareFeed(callFeed: CallFeed) {
+    private removeScreenshareFeed(callFeed: CallFeed): void {
         const feedIndex = this.screenshareFeeds.findIndex((feed) => feed.userId === callFeed.userId);
 
         if (feedIndex === -1) {
@@ -1278,7 +1284,7 @@ export class GroupCall extends TypedEventEmitter<
      * Participant Management
      */
 
-    private addParticipant(member: RoomMember) {
+    private addParticipant(member: RoomMember): void {
         if (this.participants.find((m) => m.userId === member.userId)) {
             return;
         }
@@ -1289,7 +1295,7 @@ export class GroupCall extends TypedEventEmitter<
         this.client.emit(GroupCallEventHandlerEvent.Participants, this.participants, this);
     }
 
-    private removeParticipant(member: RoomMember) {
+    private removeParticipant(member: RoomMember): void {
         const index = this.participants.findIndex((m) => m.userId === member.userId);
 
         if (index === -1) {
diff --git a/src/webrtc/groupCallEventHandler.ts b/src/webrtc/groupCallEventHandler.ts
index 86df72289..6a1084152 100644
--- a/src/webrtc/groupCallEventHandler.ts
+++ b/src/webrtc/groupCallEventHandler.ts
@@ -55,7 +55,7 @@ export class GroupCallEventHandler {
     // and get
     private roomDeferreds = new Map<string, RoomDeferred>();
 
-    constructor(private client: MatrixClient) { }
+    public constructor(private client: MatrixClient) { }
 
     public async start(): Promise<void> {
         // We wait until the client has started syncing for real.
@@ -66,7 +66,7 @@ export class GroupCallEventHandler {
         if (this.client.getSyncState() !== SyncState.Syncing) {
             logger.debug("Waiting for client to start syncing...");
             await new Promise<void>(resolve => {
-                const onSync = () => {
+                const onSync = (): void => {
                     if (this.client.getSyncState() === SyncState.Syncing) {
                         this.client.off(ClientEvent.Sync, onSync);
                         return resolve();
@@ -192,7 +192,7 @@ export class GroupCallEventHandler {
         return groupCall;
     }
 
-    private onRoomsChanged = (room: Room) => {
+    private onRoomsChanged = (room: Room): void => {
         this.createGroupCallForRoom(room);
     };
 
diff --git a/src/webrtc/mediaHandler.ts b/src/webrtc/mediaHandler.ts
index c4b912ef3..c7c84876b 100644
--- a/src/webrtc/mediaHandler.ts
+++ b/src/webrtc/mediaHandler.ts
@@ -56,11 +56,11 @@ export class MediaHandler extends TypedEventEmitter<
     public userMediaStreams: MediaStream[] = [];
     public screensharingStreams: MediaStream[] = [];
 
-    constructor(private client: MatrixClient) {
+    public constructor(private client: MatrixClient) {
         super();
     }
 
-    public restoreMediaSettings(audioInput: string, videoInput: string) {
+    public restoreMediaSettings(audioInput: string, videoInput: string): void {
         this.audioInput = audioInput;
         this.videoInput = videoInput;
     }
@@ -275,7 +275,7 @@ export class MediaHandler extends TypedEventEmitter<
     /**
      * Stops all tracks on the provided usermedia stream
      */
-    public stopUserMediaStream(mediaStream: MediaStream) {
+    public stopUserMediaStream(mediaStream: MediaStream): void {
         logger.log(`mediaHandler stopUserMediaStream stopping stream ${mediaStream.id}`);
         for (const track of mediaStream.getTracks()) {
             track.stop();
@@ -333,7 +333,7 @@ export class MediaHandler extends TypedEventEmitter<
     /**
      * Stops all tracks on the provided screensharing stream
      */
-    public stopScreensharingStream(mediaStream: MediaStream) {
+    public stopScreensharingStream(mediaStream: MediaStream): void {
         logger.debug("Stopping screensharing stream", mediaStream.id);
         for (const track of mediaStream.getTracks()) {
             track.stop();
@@ -352,7 +352,7 @@ export class MediaHandler extends TypedEventEmitter<
     /**
      * Stops all local media tracks
      */
-    public stopAllStreams() {
+    public stopAllStreams(): void {
         for (const stream of this.userMediaStreams) {
             logger.log(`mediaHandler stopAllStreams stopping stream ${stream.id}`);
             for (const track of stream.getTracks()) {
diff --git a/yarn.lock b/yarn.lock
index 24a08eb42..56821e35f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3278,10 +3278,10 @@ eslint-plugin-import@^2.26.0:
     resolve "^1.22.0"
     tsconfig-paths "^3.14.1"
 
-eslint-plugin-matrix-org@^0.7.0:
-  version "0.7.0"
-  resolved "https://registry.yarnpkg.com/eslint-plugin-matrix-org/-/eslint-plugin-matrix-org-0.7.0.tgz#4b7456b31e30e7575b62c2aada91915478829f88"
-  integrity sha512-FLmwE4/cRalB7J+J1BBuTccaXvKtRgAoHlbqSCbdsRqhh27xpxEWXe08KlNiET7drEnnz+xMHXdmvW469gch7g==
+eslint-plugin-matrix-org@^0.8.0:
+  version "0.8.0"
+  resolved "https://registry.yarnpkg.com/eslint-plugin-matrix-org/-/eslint-plugin-matrix-org-0.8.0.tgz#daa1396900a8cb1c1d88f1a370e45fc32482cd9e"
+  integrity sha512-/Poz/F8lXYDsmQa29iPSt+kO+Jn7ArvRdq10g0CCk8wbRS0sb2zb6fvd9xL1BgR5UDQL771V0l8X32etvY5yKA==
 
 eslint-plugin-unicorn@^44.0.2:
   version "44.0.2"