楼主参考下
http://www.zhangxinxu.com/wordpress/2010/07/%E5%9B%A2%E8%B4%AD%E7%B1%BB%E7%BD%91%E7%AB%99%E5%80%92%E8%AE%A1%E6%97%B6%E7%9A%84js%E5%AE%9E%E7%8E%B0/
http://www.zhangxinxu.com/wordpress/2010/07/%E5%9B%A2%E8%B4%AD%E7%B1%BB%E7%BD%91%E7%AB%99%E5%80%92%E8%AE%A1%E6%97%B6%E7%9A%84js%E5%AE%9E%E7%8E%B0/
<a href="/" id="b" target= "_blank">aaaaaa<a>
<script>
var k=10,i;
i= setInterval(function(){document.getElementById('a').innerText=k;if(k<1){clearInterval(i);document.getElementById('b').href="javascript:alert(1)";}k--;},1000)
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head><body>
<span id="test"></span>
<script>
var a=4,span=document.getElementById('test');
function t(){
var arg=arguments;
window.setTimeout(function(){
span.innerHTML=a--;
if(a){
arg.callee();
}
},1000);
}
t();
</script>
</body>
</html>