A cross-browser function to retrieve the window's `scrollTop`

ScrollTop.js

function getScrollTop() {
	if (typeof window.pageYOffset !== 'undefined'){
		return window.pageYOffset;
	} else {
		var iequirks = document.body;
		var iedoctype = document.documentElement;
		var doc = (iedoctype.clientHeight) ? iedoctype : iequirks;
		return doc.scrollTop;
	}
}