JS定时关闭窗口

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <style type ="text/css" >
    .main{ background-color:Silver; width :200px; height :100px; margin-left:40%; margin-top :200px; text-align :center;}
    </style>
    <script src="js/ui/jquery-1.7.1.min.js" type="text/javascript"></script>
    <script language="javascript" type="text/javascript">
        var n = 3;
        function showTime() {
            n--;
            $('#divMain').html(n + ' 秒后关闭窗口');
            if (n == 0) 
                window.close();
            else
                setTimeout('showTime()', 1000);
        }
    </script>
</head>
<body onload ="showTime()">
    <form id="form1" runat="server">
    <div id ="divMain" class ="main" >
          
    </div>
    </form>
</body>
</html>