code: function (eventType, evt) {
      if (!this.eventListeners) {
        this.eventListeners = {};
      }
      if (!evt) {
        evt = {};
      }
      evt.type = eventType;
      if (!evt.source) {
        evt.source = this;
      }
      var events = this.eventListeners[eventType];
      if (events) {
        var len = events.length;
        for (var i = 0; i < len; i++) {
          events[i].handler.apply(this, [evt]);
        }
      }
      return this;
    }
docs: Fire an event.
  
  @param eventType
  @param evt