message: Clean up useEventEmitter
diff: +/*
  +Copyright 2019 The Matrix.org Foundation C.I.C.
  +
  +Licensed under the Apache License, Version 2.0 (the "License");
  +you may not use this file except in compliance with the License.
  +You may obtain a copy of the License at
  +
  + http://www.apache.org/licenses/LICENSE-2.0
  +
  +Unless required by applicable law or agreed to in writing, software
  +distributed under the License is distributed on an "AS IS" BASIS,
  +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  +See the License for the specific language governing permissions and
  +limitations under the License.
  +*/
  +
  import {useRef, useEffect} from "react";
  // Hook to wrap event emitter on and removeListener in hook lifecycle
  @@ -6,19 +22,12 @@ export const useEventEmitter = (emitter, eventName, handler) => {
  const savedHandler = useRef();
  // Update ref.current value if handler changes.
  - // This allows our effect below to always get latest handler ...
  - // ... without us needing to pass it in effect deps array ...
  - // ... and potentially cause effect to re-run every render.
  useEffect(() => {
  savedHandler.current = handler;
  }, [handler]);
  useEffect(
  () => {
  - // Make sure element supports on
  - const isSupported = emitter && emitter.on;
  - if (!isSupported) return;
  -
  // Create event listener that calls handler function stored in ref
  const eventListener = event => savedHandler.current(event);
  