offset[Left/Top]

index.js

var getScrollX
	, getScrollX
	, _document_documentElement = document.documentElement
;

document.compatMode === "CSS1Compat" ?
	((_getScrollX = function(){return _document_documentElement.scrollLeft}), (_getScrollY = function(){return _document_documentElement.scrollTop}))
	:
	((_getScrollX = function(){return document.body.scrollTop}), (_getScrollY = function(){return document.body.scrollLeft}))
;

/**
 * http://javascript.ru/ui/offset#popytka-2:-getboundingclientrect
 * @param {Node} elem
 * @param {boolean=} X_else_Y
 * @return {number}
 */
function unsafeGetOffsetRect(elem, X_else_Y) {
	if("element" in elem && "defaults" in elem && "document" in elem) {//IE < 8 with htc -> this instanceof DispHTCDefaultDispatch
		elem = elem["element"];
	}

	var box = elem.getBoundingClientRect()//It might be an error here
		, _body
		, _documentElement
		, _doc
		;

	if((_doc = elem.ownerDocument) !== document) {
		_body = _doc && _doc.body;
		_documentElement = _doc && _doc.documentElement;
		if(!_body || !_documentElement) {
			return X_else_Y ? box.left : box.top;
		}
	}
	else {
		_body = document.body;
		_documentElement = _document_documentElement;
	}


	return X_else_Y ?
		(box.left + _getScrollX() - (_documentElement.clientLeft || _body.clientLeft || 0))
		:
		(box.top + _getScrollY() - (_documentElement.clientTop || _body.clientTop || 0))
		;
}

/**
 * http://javascript.ru/ui/offset#popytka-1-summiruem-offset-y
 * @param {Node} elem
 * @param {boolean=} X_else_Y
 * @return {number}
 */
function getOffsetSum(elem, X_else_Y) {
	var result = 0,
		prop = X_else_Y ? "offsetLeft" : "offsetTop";

	while(elem) {
		result = result + parseInt(elem[prop], 10);
		elem = elem.offsetParent;
	}

	return result;
}

/**
 * @param {Node} elem
 * @param {boolean=} X_else_Y
 * @return {number}
 */
function safeGetOffsetRect(elem, X_else_Y) {
	var result;
	try {
		result = unsafeGetOffsetRect(elem, X_else_Y);
	}
	catch(e) {
		result = getOffsetSum(elem, X_else_Y);
	}
	return result;

	//Broken impimintation up here
	//Here right impl from jQuery
	//TODO::

	/*
	 jQuery.fn.extend({

	 position: function() {
	 if ( !this[0] ) {
	 return null;
	 }

	 var elem = this[0],

	 // Get *real* offsetParent
	 offsetParent = this.offsetParent(),

	 // Get correct offsets
	 offset       = this.offset(),
	 parentOffset = rroot.test(offsetParent[0].nodeName) ? { top: 0, left: 0 } : offsetParent.offset();

	 // Subtract element margins
	 // note: when an element has margin: auto the offsetLeft and marginLeft
	 // are the same in Safari causing offset.left to incorrectly be 0
	 offset.top  -= parseFloat( jQuery.css(elem, "marginTop") ) || 0;
	 offset.left -= parseFloat( jQuery.css(elem, "marginLeft") ) || 0;

	 // Add offsetParent borders
	 parentOffset.top  += parseFloat( jQuery.css(offsetParent[0], "borderTopWidth") ) || 0;
	 parentOffset.left += parseFloat( jQuery.css(offsetParent[0], "borderLeftWidth") ) || 0;

	 // Subtract the two offsets
	 return {
	 top:  offset.top  - parentOffset.top,
	 left: offset.left - parentOffset.left
	 };
	 },

	 offsetParent: function() {
	 return this.map(function() {
	 var offsetParent = this.offsetParent || document.body;
	 while ( offsetParent && (!rroot.test(offsetParent.nodeName) && jQuery.css(offsetParent, "position") === "static") ) {
	 offsetParent = offsetParent.offsetParent;
	 }
	 return offsetParent;
	 });
	 }
	 });
	 */

}