<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />
<title></title>
<style type="text/css">
* { padding:0; margin:0; }
#box { position:relative; margin:50px; }
#pop { display:none; position:absolute; left:200px; top:100px; width:120px; height:120px; border:2px solid #ccc; background:#eee; }
</style>
<script type="text/javascript">
window.onload=function(){
var oBox=document.getElementById("box");
var obj=document.getElementById("pop");
var oBtn=document.getElementById("click");

oBtn.onclick=function(){
obj.style.display="block";
}
document.onclick=function(event){
//
var e=event || window.event;//兼容ie和非ie的event
var aim=e.srcElement || e.target; //兼容ie和非ie的事件源
//
if(e.srcElement){
var aim=e.srcElement;
if(aim!=oBtn && aim!=obj){
obj.style.display="none";
}
}else{
var aim=e.target;
if(aim!=oBtn && aim!=obj){
obj.style.display="none";
}
}
}
}
</script>
</head>
<body>
<div id="box">
<a href="javascript:;" id="click" >点击弹出</a>
<div id="pop">
弹出层内容呢
</div>
</div>
</body>
</html>