Delaying events

delay.js

function timeout(millis) {
  return new Promise((resolve, reject) => {
    setTimeout(resolve, millis);
  });
}

class Dispatcher {
  constructor() {
    this.listeners = [];
    this.delayedListeners = [];
    this.delayedEvents = [];
  }

  fireEvent(payload) {
    const event = {payload: payload, occuredTime: new Date()};
    this.listeners.forEach(f => f(event)); // notify all listeners
    this._fireDelay(event);
  }

  _fireDelay(event) {
    this.delayedEvents.push(event);
    timeout(500).then(() => {
      const delayedEvents = this.delayedEvents;
      this.delayedEvents = [];
      if (delayedEvents.length > 0) {
        this.delayedListeners.forEach(f => f(delayedEvents));
      }
    })
  }

  onAllEvent(callback) {
    this.delayedListeners.push(callback);
  }

  onEvent(callback) {
    this.listeners.push(callback);
  }
}

const dispatcher = new Dispatcher();

// dispatcher.onEvent(event => console.log('onEvent:', event));
dispatcher.onAllEvent(events => console.log('onAllEvent:', events));

console.log('Firing events');
timeout(10).then(() => dispatcher.fireEvent('a.txt'));
timeout(200).then(() => dispatcher.fireEvent('b.txt'));
timeout(300).then(() => dispatcher.fireEvent('c.txt'));
timeout(700).then(() => dispatcher.fireEvent('d.txt'));
timeout(1500).then(() => dispatcher.fireEvent('e.txt'));