code: function setupEvent(event_type) {
    var event = void 0;
  
    if (exists(document.createEvent)) {
      // modern browsers
      event = document.createEvent('HTMLEvents');
      event.initEvent(event_type, true, true);
    } else if (exists(document.createEventObject)) {
      // IE9-
      event = document.createEventObject();
      event.eventType = event_type;
      event.eventName = event_type;
    }
    return event;
  }
docs: Cross-browser bridge that creates event object
  @param {string} event_type Event identifier
  @returns {Event} Event object
  @private