关于弹出窗口自动关闭的问题！！

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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>弹出菜单自动关闭</title>
<script language="javascript">
  child=window.open("http://www.sina.com.cn","sina","width=300,height=300,toolbar=no,menubar=no,scrollbars=no,resize=no,location=no,status=no");
  function closeit(){
   setTimeout("child.close()",10000);
  }
</script>
</head><body onLoad="closeit()">
aaaaa
</body>
</html>