Event Listener polyfill

eventListener.js

// addEventListener polyfill IE6+
!window.addEventListener && (function (window, document) {
	function Event(e, element) {
		var instance = this;

		for (property in e) {
			instance[property] = e[property];
		}

		instance.currentTarget =  element;
		instance.target = e.srcElement || element;
		instance.timeStamp = +new Date;

		instance.preventDefault = function () {
			e.returnValue = false;
		};
		instance.stopPropagation = function () {
			e.cancelBubble = true;
		};
	}

	function addEventListener(type, listener) {
		var
		element = this,
		listeners = element.listeners = element.listeners || [],
		index = listeners.push([listener, function (e) {
			listener.call(element, new Event(e, element));
		}]) - 1;

		element.attachEvent('on' + type, listeners[index][1]);
	}

	function removeEventListener(type, listener) {
		for (var element = this, listeners = element.listeners || [], length = listeners.length, index = 0; index < length; ++index) {
			if (listeners[index][0] === listener) {
				element.detachEvent('on' + type, listeners[index][1]);
			}
		}
	}

	window.addEventListener = document.addEventListener = addEventListener;
	window.removeEventListener = document.removeEventListener = removeEventListener;

	if ('Element' in window) {
		Element.prototype.addEventListener    = addEventListener;
		Element.prototype.removeEventListener = removeEventListener;
	} else {
		var
		head = document.getElementsByTagName('head')[0],
		style = document.createElement('style');

		head.insertBefore(style, head.firstChild);

		style.styleSheet.cssText = '*{-ms-event-prototype:expression(!this.addEventListener&&(this.addEventListener=addEventListener)&&(this.removeEventListener=removeEventListener))}';
	}
})(window, document) && scrollBy(0, 0);

Thanks for this polyfill - the CSS expression stuff is a stroke of genius. I've forked it to use it in a project of my own (you don't specify a license but I assume that's kosher...).

There's one bit I don't quite understand: what's up with scrollBy(0, 0)? The IIFE returns undefined, so the && operator short-circuits and the code is never reached. What does it do?

Keep in mind, for...in loops are supported by IE10+. So this polyfill will not work unless you replace then with normal for(;;) loops.

will this work on DOMContentLoaded, readystatechange, progress or what?