For every Browser except lower than IE9, which you shouldn't support anyway (imho).

customEventData.js

var evt = document.createEvent('Event');
evt.initEvent('bbEvent', true, true);

var customEventData = {
  dataString: "Hello",
  dataArray: ['W', 'o', 'r', 'l', 'd']
}
evt.data = customEventData;
element.dispatchEvent(evt);

window.addEventListener('bbEvent', function (event) {
  console.log(event.data);
}