Position of element in javascript

function ( el ) {
    var x = 0;
    var y = 0;
    while( el && !isNaN( el.offsetLeft ) && !isNaN( el.offsetTop ) ) {
        x += el.offsetLeft - el.scrollLeft;
        y += el.offsetTop - el.scrollTop;
        el = el.offsetParent;
    }
    return { top: y, left: x };
}