窗口关闭问题？

<body onunload='closeAll()'>
<a href='#' onclick="w1=window.open('','')">
<a href='#' onclick="w2=window.open('','')">
<a href='#' onclick="w3=window.open('','')">
<script>
var w1 = null;
var w2 = null;
var w3 = null;
function closeAll()
{
   if (w1!=null)
      w1.close();
   if (w2!=null)
      w2.close();
   if (w3!=null)
      w3.close();
}
</script>