Simple Event Emitter Improved

event-emitter-improved.js

// make EE singelton, add .off method

let instance = null;

class EventEmitter {
  constructor() {
    // ensure we have only one instance (singelton pattern)
    if (!instance) {
      instance = this;
    }
    this.events = {};
    return instance;
  }
  // unsubscribe 
  off(name, fn) {
    this.events[name] = this.events[name] || [];
    let index = this.events[name].indexOf(fn);
    this.events[name].splice(index, 1);
  }
  on(name, fn) {
    this.events[name] = this.events[name] || [];
    this.events[name].push(fn);
  };
  trigger(name, args) {
    this.events[name] = this.events[name] || [];
    this.events[name].forEach((fn) => fn(args));
  };
}

real-life-usage.js

// EE in real life. 
// Store - it's out model.

class Store extends EventEmitter {
    constructor(initalState) {
      super()
      this.__state = initalState;
    };
    get state() {
      return this.__state
    };
    set state(state) {
      this.trigger('update', state);
      this.__state =  state;
    }
}

var store = new Store({});
store.on('update', function(newState) {
  console.log('newState', newState);
  // update DOM
});
// set new state
store.state = { name: 'Vasya Pupkin' };
store.state = { name: 'Petya Ivanov' };