hasListeners(eventName) {
    assertEventName(eventName, this[EVENT_NAMES]);

    const events = this[EVENTS];

    return events.has(eventName) && events.get(eventName).size > 0;
  }
Returns `true` if there are any listeners for the event named `eventName`
or `false` otherwise.

@param {String} eventName - The name of the event
@returns {Boolean}