Here’s how I do it:
// Based on: http://www.quirksmode.org/js/findpos.html
var getCumulativeOffset = function (obj) {
var left, top;
left = top = 0;
if (obj.offsetParent) {
do {
left += obj.offsetLeft;
top += obj.offsetTop;
} while (obj = obj.offsetParent);
}
return {
x : left,
y : top
};
};