io trovai questo codice e funziona
codice:
function findLeftPosition(obj) {
  return findPosition(obj, "offsetLeft");
}
function findTopPosition(obj) {
  return findPosition(obj, "offsetTop");
}
function findPosition(obj, na) {
  var wb = 0;
  while (obj) {
    wb += obj[na];
    obj = obj.offsetParent;
  }
  return wb;
}