// It works on IE 9 and HTML 5 browsers in general.
Rx.Observable.fromHTMLEvent = function (element, eventName) {
  return Rx.Observable.create(function (observer) {
    // The line below should work but it gives an error. So we did a workaround.
    // var observer_onNext = observer.onNext;
    var observer_onNext = function (data) { observer.onNext(data); };
    element.addEventListener(eventName, observer_onNext, false);
    return Rx.Disposable.create(function () {
      element.removeEventListener(eventName, observer_onNext);
    });
  });
};