Q: Create Event Emitter

NOTE: just pasted this in... may need to be reviewed.

class EventEmitter {
  constructor() {
    this.subscriptions = new Map();
  }

  subscribe(eventName, callback) {
    if (!this.subscriptions.get(eventName)) {
      this.subscriptions.set(eventName, []);
    }

    this.subscriptions.get(eventName).push(callback);

    return {
      release: () => {
        const callbacks = this.subscriptions.get(eventName);
        const index = callbacks.indexOf(callback);
        if (index > 1) {
          callbacks.splice(index, 1);
        }
        if (callbacks.size === 0) {
          this.subscriptions.delete(eventName);
        }
      },
    };
  }

  emit(eventName, ...args) {
    const callbacks = this.subscriptions.get(eventName);
    if (!callbacks) {
      return;
    }
    for (let callback of callbacks) {
      callback(...args);
    }
  }
}

const callback1 = (...args) => {
  console.log('callback1 ', args);
};
const callback2 = (...args) => {
  console.log('callback2 ', args);
};
const emitter = new EventEmitter();
const sub1 = emitter.subscribe('event1', callback1);
const sub2 = emitter.subscribe('event2', callback2);

// same callback could subscribe
// on same event multiple times
const sub3 = emitter.subscribe('event1', callback2);

emitter.emit('event1', 1, 2);
sub3.release();
emitter.emit('event2', 2, 2);