Update member count on room summary update

src/hooks/useRoomMembers.ts

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { useCallback, useState } from "react";
+import { useCallback, useMemo, useState } from "react";
 import { Room, RoomEvent, RoomMember, RoomStateEvent } from "matrix-js-sdk/src/matrix";
 import { throttle } from "lodash";
 
@@ -44,27 +44,40 @@ type RoomMemberCountOpts = {
     throttleWait?: number;
 };
 
-// Hook to simplify watching Matrix Room joined member count
+/**
+ * Returns a count of members in a given room
+ * @param room the room to track.
+ * @param opts The options.
+ * @returns the room member count.
+ */
 export const useRoomMemberCount = (room: Room, opts: RoomMemberCountOpts = { throttleWait: 250 }): number => {
     const [count, setCount] = useState<number>(room.getJoinedMemberCount());
 
     const { throttleWait } = opts;
 
-    const onMembershipUpdate = useCallback(() => {
+    const updateMembershipCount = useCallback((): void => {
         setCount(room.getJoinedMemberCount());
     }, [room]);
 
-    useTypedEventEmitter(
-        room.currentState,
-        RoomStateEvent.Members,
-        throttle(onMembershipUpdate, throttleWait, { leading: true, trailing: true }),
+    const throttledUpdate = useMemo(
+        () =>
+            throttle(
+                () => {
+                    updateMembershipCount();
+                },
+                throttleWait,
+                { leading: true, trailing: true },
+            ),
+        [throttleWait, updateMembershipCount],
     );
 
-    useTypedEventEmitter(
-        room,
-        RoomEvent.Summary,
-        throttle(onMembershipUpdate, throttleWait, { leading: true, trailing: true }),
-    );
+    useTypedEventEmitter(room.currentState, RoomStateEvent.Members, throttledUpdate);
+
+    /**
+     * `room.getJoinedMemberCount()` caches the member count behind the room summary
+     * So we need to re-compute the member count when the summary gets updated
+     */
+    useTypedEventEmitter(room, RoomEvent.Summary, throttledUpdate);
     return count;
 };