js擷取頁面元素位置函數

　用Javascript擷取指定頁面元素的位置是一個非常常見的需求，本文介紹的函數能夠準確返回一個元素相對於整個文檔左上方的座標，即元素的 top 、left 的位置，而且能夠相容瀏覽器，相信對新手非常有用。

function getElementPos(elementId) {
 var ua = navigator.userAgent.toLowerCase();
 var isOpera = (ua.indexOf('opera') != -1);
 var isIE = (ua.indexOf('msie') != -1 && !isOpera); // not opera spoof
 var el = document.getElementById(elementId);
 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]};
}

使用樣本

var pos=getElementPos("divId");
alert("距左邊距離"+ pos.x +",距上邊距離"+pos.y);