index.js

var NativeCustomEvent = global.CustomEvent;

function useNative () {
  try {
    var p = new NativeCustomEvent('cat', { detail: { foo: 'bar' } });
    return  'cat' === p.type && 'bar' === p.detail.foo;
  } catch (e) {
  }
  return false;
}

/**
 * Cross-browser `CustomEvent` constructor.
 *
 * https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent.CustomEvent
 *
 * @public
 */

module.exports = useNative() ? NativeCustomEvent :

// IE >= 9
'undefined' !== typeof document && 'function' === typeof document.createEvent ? function CustomEvent (type, params) {
  var e = document.createEvent('CustomEvent');
  if (params) {
    e.initCustomEvent(type, params.bubbles, params.cancelable, params.detail);
  } else {
    e.initCustomEvent(type, false, false, void 0);
  }
  return e;
} :

// IE <= 8
function CustomEvent (type, params) {
  var e = document.createEventObject();
  e.type = type;
  if (params) {
    e.bubbles = Boolean(params.bubbles);
    e.cancelable = Boolean(params.cancelable);
    e.detail = params.detail;
  } else {
    e.bubbles = false;
    e.cancelable = false;
    e.detail = void 0;
  }
  return e;
}