QQ窗口震动效果

<img  id="win" style='position:relative' src="http://www.uanv.net/web/qq.jpg">
<br /><br />
<button onclick="zd()">振动</button>
<script >
function zd(u){ 
 var a=['top','left'],b=0;
 u=setInterval(function(){
  document.getElementById('win').style[a[b%2]]=(b++)%4<2?0:4;
  if(b>15){clearInterval(u);b=0}
 },32)
}
</script>