SimpleEventSystem.js

/**
 * Simple Event system similar to
 * DOM's synthetic events.
 */
export class Event {
  constructor(name) {
    this.name = name;
    this.callbacks = [];
  }
  registerCallback(callback) {
    this.callbacks.push(callback);
  }
}

export class EventReactor {
  constructor() {
    this.events = {};
  }

  registerEvent = function (eventName) {
    var event = new Event(eventName);
    this.events[eventName] = event;
  };

  dispatchEvent = function (eventName, eventArgs) {
    this.events[eventName].callbacks.forEach(function (callback) {
      callback(eventArgs);
    });
  };

  addEventListener = function (eventName, callback) {
    this.registerEvent(eventName);
    this.events[eventName].registerCallback(callback);
  };
}

//usage
const reactor = new EventReactor();
reactor.addEventListener('foo', (data)=> { console.log('foo fired with', data) }; // prints foo fired with {name: 'ragzzy', id:42}
// to emit the event
reactor.dispatchEvent('foo', {name: 'ragzzy', id: 42})