snippet.js

// -- this --

function topOffset(obj) {
  return obj ? obj.offsetTop + topOffset(obj.offsetParent) : 0;
}  

// --- or this --

function topOffset(obj) {
  var curtop = 0;
  if (obj.offsetParent) {
    do {
      curtop += obj.offsetTop;
    } while (obj = obj.offsetParent);
    return curtop;
  }
  return 0;
}