Implement EventEmitter

EventEmitter.js

class EventEmitter {
  constructor (isAsync = false) {
    this.events = new Map();
    this.isAsync = isAsync;  // Allow to notify listener async
  }
  
  /*
  * Subcribe a callback to an event. Callback will not be duplicate.
  * return unsibcribe function
  * Usage: const unsub = ee.subcribe(eventName, callback);
  * To unsubcribe: unsub()
  */
  subcribe (event, callback) {
    const listeners = this.events.get(event) || new Set();
    listeners.add(callback);
    this.events.set(event, listeners);
    return this.unsubcribe.bind(this, event, callback);
  }
  
  unsubcribe (event, callback) {
    const listeners = this.events.get(event);
    if (listeners !== undefined) {
      listeners.delete(callback);
    }
  }
  
  emit (event, ...args) {
    const listeners = this.events.get(event);
    if (listeners !== undefined) {
      // if a callback got unsubcribe while iterate it wont' get call
      // use [...listeners].forEach to prevent this.
      if (this.isAsync) {
        // Wrap callback inside promises for async call
        Promise.all(
          [...listeners].map(
            async (callback) => new Promise((approve, reject) => {
                approve(callback.apply(null, args));
            })
          )
        );
      } else {
        listeners.forEach((callback) => {
          try {
            callback.apply(null, args);
          } catch (err) {
            // Do something.
          }
        });
      }
    }
  }
}



/* Async test */
async function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

const ee = new EventEmitter(true);
const unsub1 = ee.subcribe('test', async () => {
    await sleep(2000);
    console.log('Sub1');
});
const unsub2 = ee.subcribe('test', () => {console.log('Sub2')});
const unsub3 = ee.subcribe('test', () => {console.log('Sub3')});

ee.emit('test')