元素距离页面的绝对距离

<style>
div{padding: 40px;position: relative}
#div1{background: red;}
#div2{background: green}
#div3{background: yellow}
</style>
<div id="div1">
<div id="div2">
<div id="div3"></div>
</div>
</div>

<script>
window.onload=function(){
var oDiv3=document.getElementById("div3");
var p=getPos(oDiv3);
alert(p.top);
function getPos(obj){
var pos={left:0,top:0};
while(obj){
pos.left+=obj.offsetLeft;
pos.top+=obj.offsetTop;
obj=obj.offsetParent;
}
return pos;
}
}
</script>