List common rooms in MemberInfo

src/utils/DMRoomMap.js

@@ -21,18 +21,13 @@ limitations under the License.
  */
 export default class DMRoomMap {
     constructor(matrixClient) {
+        this.roomToUser = null;
+
         const mDirectEvent = matrixClient.getAccountData('m.direct');
         if (!mDirectEvent) {
             this.userToRooms = {};
-            this.roomToUser = {};
         } else {
             this.userToRooms = mDirectEvent.getContent();
-            this.roomToUser = {};
-            for (const user of Object.keys(this.userToRooms)) {
-                for (const roomId of this.userToRooms[user]) {
-                    this.roomToUser[roomId] = user;
-                }
-            }
         }
     }
 
@@ -41,6 +36,24 @@ export default class DMRoomMap {
     }
 
     getUserIdForRoomId(roomId) {
+        if (this.roomToUser == null) {
+            // we lazily populate roomToUser so you can use
+            // this class just to call getDMRoomsForUserId
+            // which doesn't do very much, but is a fairly
+            // convenient wrapper and there's no point
+            // iterating through the map if getUserIdForRoomId()
+            // is never called.
+            this._populateRoomToUser();
+        }
         return this.roomToUser[roomId];
     }
+
+    _populateRoomToUser() {
+        this.roomToUser = {};
+        for (const user of Object.keys(this.userToRooms)) {
+            for (const roomId of this.userToRooms[user]) {
+                this.roomToUser[roomId] = user;
+            }
+        }
+    }
 }