Absolute Position of a DOM Element

function __getIEVersion() {
    var rv = -1; // Return value assumes failure.
    if (navigator.appName == 'Microsoft Internet Explorer') {
        var ua = navigator.userAgent;
        var re = new RegExp("MSIE ([0-9]{1,}[\.0-9]{0,})");
        if (re.exec(ua) != null)
            rv = parseFloat(RegExp.$1);
    }
    return rv;
}

function __getOperaVersion() {
    var rv = 0; // Default value
    if (window.opera) {
        var sver = window.opera.version();
        rv = parseFloat(sver);
    }
    return rv;
}

var __userAgent = navigator.userAgent;
var __isIE =  navigator.appVersion.match(/MSIE/) != null;
var __IEVersion = __getIEVersion();
var __isIENew = __isIE && __IEVersion >= 8;
var __isIEOld = __isIE && !__isIENew;

var __isFireFox = __userAgent.match(/firefox/i) != null;
var __isFireFoxOld = __isFireFox && ((__userAgent.match(/firefox\/2./i) != null) || (__userAgent.match(/firefox\/1./i) != null));
var __isFireFoxNew = __isFireFox && !__isFireFoxOld;

var __isWebKit =  navigator.appVersion.match(/WebKit/) != null;
var __isChrome =  navigator.appVersion.match(/Chrome/) != null;
var __isOpera =  window.opera != null;
var __operaVersion = __getOperaVersion();
var __isOperaOld = __isOpera && (__operaVersion < 10);

function __parseBorderWidth(width) {
    var res = 0;
    if (typeof(width) == "string" && width != null && width != "" ) {
        var p = width.indexOf("px");
        if (p >= 0) {
            res = parseInt(width.substring(0, p));
        }
        else {
     		//do not know how to calculate other values (such as 0.5em or 0.1cm) correctly now
    		//so just set the width to 1 pixel
            res = 1; 
        }
    }
    return res;
}


//returns border width for some element
function __getBorderWidth(element) {
	var res = new Object();
	res.left = 0; res.top = 0; res.right = 0; res.bottom = 0;
	if (window.getComputedStyle) {
		//for Firefox
		var elStyle = window.getComputedStyle(element, null);
		res.left = parseInt(elStyle.borderLeftWidth.slice(0, -2));  
		res.top = parseInt(elStyle.borderTopWidth.slice(0, -2));  
		res.right = parseInt(elStyle.borderRightWidth.slice(0, -2));  
		res.bottom = parseInt(elStyle.borderBottomWidth.slice(0, -2));  
	}
	else {
		//for other browsers
		res.left = __parseBorderWidth(element.style.borderLeftWidth);
		res.top = __parseBorderWidth(element.style.borderTopWidth);
		res.right = __parseBorderWidth(element.style.borderRightWidth);
		res.bottom = __parseBorderWidth(element.style.borderBottomWidth);
	}
   
	return res;
}

//returns the absolute position of some element within document
function getElementAbsolutePos(element) {
	var res = new Object();
	res.x = 0; res.y = 0;
	if (element !== null) { 
		if (element.getBoundingClientRect) {
			var viewportElement = document.documentElement;  
 	        var box = element.getBoundingClientRect();
		    var scrollLeft = viewportElement.scrollLeft;
 		    var scrollTop = viewportElement.scrollTop;

		    res.x = box.left + scrollLeft;
		    res.y = box.top + scrollTop;

		}
		else { //for old browsers
			res.x = element.offsetLeft;
			res.y = element.offsetTop;
			
			var parentNode = element.parentNode;
			var borderWidth = null;

			while (offsetParent != null) {
				res.x += offsetParent.offsetLeft;
				res.y += offsetParent.offsetTop;
				
				var parentTagName = offsetParent.tagName.toLowerCase();	

				if ((__isIEOld && parentTagName != "table") || ((__isFireFoxNew || __isChrome) && parentTagName == "td")) {		    
					borderWidth = kGetBorderWidth(offsetParent);
					res.x += borderWidth.left;
					res.y += borderWidth.top;
				}
				
				if (offsetParent != document.body && offsetParent != document.documentElement) {
					res.x -= offsetParent.scrollLeft;
					res.y -= offsetParent.scrollTop;
				}


				//next lines are necessary to fix the problem with offsetParent
				if (!__isIE && !__isOperaOld || __isIENew) {
					while (offsetParent != parentNode && parentNode !== null) {
						res.x -= parentNode.scrollLeft;
						res.y -= parentNode.scrollTop;
						if (__isFireFoxOld || __isWebKit) {
							borderWidth = kGetBorderWidth(parentNode);
							res.x += borderWidth.left;
							res.y += borderWidth.top;
						}
						parentNode = parentNode.parentNode;
					}    
				}

				parentNode = offsetParent.parentNode;
				offsetParent = offsetParent.offsetParent;
			}
		}
	}
    return res;
}