奇怪 为什么运行时有2个窗口啊

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<head runat="server">
    <title>无标题页</title>
</head>
<body  onload="begintimer()">
 <script   type ="text/javascript"  >
  
        var templ='0:2:10'
        var parselimit=templ.split(":")
        parselimit = parselimit[0]*3600 + parselimit[1]*60 + parselimit[2]*1
     
        function begintimer()
        {
            if (parselimit==1)
            {
             
              window.location="Default3.aspx"
            }
            else
            { 
               parselimit-=1
               if(parselimit==2*60)
               {   
                 alert("距离考试结束还有2分钟。");          
               
               }
               if(parselimit==1*60)
               { 
                  alert("距离考试结束还有1分钟。");             
               }
               setTimeout("begintimer()",1000)
               
             
            }
        }
        
    </script>
    <form   id="form1" runat="server">
     
    </form>
</body>
</html>