var EventEmitter = function () {
  this.events = {};
}

EventEmitter.prototype.on = function (eventName, cb) {
  if (this.events[eventName]) {
    this.events[eventName].push(cb);
  } else {
    this.events[eventName] = [cb];
  }
}

EventEmitter.prototype.off = function (eventName, cb) {
  if (this.events[eventName]) {
    var i = this.events[eventName].indexOf(cb);
    this.events[eventName].splice(i, 1);
  }
}
EventEmitter.prototype.trigger = function (eventName, data) {
  if (this.events[eventName]) {
    this.events[eventName].forEach(function (cb) {
      cb(data);
    }, this);
  }
}