gistfile1.txt

function* watchEvents(): any {
  const initial = yield call(ExternalApi.getCurrent);
  yield put(receiveEvent(initial);
  
  const chan = yield call(setupEvents);
  
  while (true) {
    const event = yield take(chan);
    yield put(receiveEvent(event));
  }
}

function setupEvents() {
  return eventChannel(listener => {
    ExternalApi.addChangeListener(listener);
    return () => {
      ExternalApi.removeChangeListener(listener);
    }
  });
}