fireEvent(eventName, data) {
      const eventRegistry = this._eventRegistry;
      const eventListeners = eventRegistry.get(eventName);
      if (!eventListeners) {
        return [];
      }
      return eventListeners.map(fn => {
        return fn.call(this, data);
      });
    }
Fires an event and returns the results of all event listeners as an array.

@param eventName the event to fire
@param data optional data to pass to each event listener
@returns {Array} an array with the results of all event listeners