js获取页面元素位置函数

　用Javascript获取指定页面元素的位置是一个非常常见的需求，本文介绍的函数能够准确返回一个元素相对于整个文档左上角的坐标，即元素的 top 、left 的位置，而且能够兼容浏览器，相信对新手非常有用。

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]};
}

使用示例

var pos=getElementPos("divId");
alert("距左边距离"+ pos.x +",距上边距离"+pos.y);