为啥会提示框会弹出2次？

<title>我们互动下</title>

<script type="text/javascript">

document.write("JS进阶篇");

var mymessage=confirm("关注JS高级篇");

if(mymessage==true)

{

    document.write("<br>已关注");

}

else

{

    document.write("<br>下次一定");

}

</script>

</head>