delayedRefCount-functional.js

function delayedRefCount(delay) {
  return (source) => {
    const subscribeUpdates = new Subject();
    let trackerConnection;
    let subscriptionTracker = subscribeUpdates.scan((total, change) => change + total, 0)
      .switchMap(count => {
        return count === 0
          ? Observable.timer(delay)
            .do(_ => source.connect().unsubscribe() || trackerConnection.unsubscribe())
          : Observable.never();
      }).publish();

    const onNewSubscriber = () => {
      source.connect();
      trackerConnection = subscriptionTracker.connect();
      subscribeUpdates.next(1);
      return function onUnsubscribe() {
         subscribeUpdates.next(-1)
      };
    };
    const observable = () => source;
    return Observable.using(onNewSubscriber, observable);
  };
}