javascript 擷取標籤具體位置

//var temp = document.getElementById("test_2");
//temp.style.position = "absolute";
//temp.style.top = pos.y + "px";
//temp.style.left = pos.x + "px";

//擷取對象的X，Y位置  接受對象 不接收ID
function getElementPos(el) {
 var ua = navigator.userAgent.toLowerCase();
 var isOpera = (ua.indexOf('opera') != -1);
 var isIE = (ua.indexOf('msie') != -1 && !isOpera); // not opera spoof
 if(el.parentNode === null || el.style.display == 'none'){
  return false;
 }
 var parent = null;
 var pos = [];
 var box;
 if(el.getBoundingClientRect){//IE
  box = el.getBoundingClientRect();
  var scrollTop = Math.max(document.documentElement.scrollTop, document.body.scrollTop);
  var scrollLeft = Math.max(document.documentElement.scrollLeft, document.body.scrollLeft);
  return {x:box.left + scrollLeft, y:box.top + scrollTop};
 }else if(document.getBoxObjectFor){// gecko
  box = document.getBoxObjectFor(el);
  var borderLeft = (el.style.borderLeftWidth)?parseInt(el.style.borderLeftWidth):0;
  var borderTop = (el.style.borderTopWidth)?parseInt(el.style.borderTopWidth):0;
  pos = [box.x - borderLeft, box.y - borderTop];
 }else{// safari & opera
  pos = [el.offsetLeft, el.offsetTop];
  parent = el.offsetParent;
  if (parent != el) {
   while (parent) {
    pos[0] += parent.offsetLeft;
    pos[1] += parent.offsetTop;
    parent = parent.offsetParent;
   }
  }
  if (ua.indexOf('opera') != -1  || ( ua.indexOf('safari') != -1 && el.style.position == 'absolute' )){
   pos[0] -= document.body.offsetLeft;
   pos[1] -= document.body.offsetTop;
  }
 }
 if (el.parentNode) { parent = el.parentNode; }
 else { parent = null; }
 while (parent && parent.tagName != 'BODY' && parent.tagName != 'HTML'){ // account for any scrolled ancestors
  pos[0] -= parent.scrollLeft;
  pos[1] -= parent.scrollTop;
  if (parent.parentNode) { parent = parent.parentNode; }
  else { parent = null; }
 }
 return {x:pos[0], y:pos[1]};
}