老师请问问题出在哪

来源：2-1 location对象属性

k1ans

2017-08-10 16:56:42

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>闪烁的文字</title>
        <style type="text/css">
            div{
                width:200px;
                height:200px;
                line-height:200px;
                border:2px solid gray;
                text-align:center;
                color:red;
            }
        </style>
    </head>
<body>
    <h3>会闪烁的文字</h3>
        <div id="text"> </div>
        <script type="text/javascript">
           var text=document.getElementById("text");
           var num=0;
        var timer=setInterval(function){
               if(num==0){
             text.innerHTML="☆☆☆今日特卖☆☆☆";
             num=1;
               }else{

                   text.innerHTML="★★★今日特卖★★★";

                   num=0;
               }
           },500);
        </script>
    </body>
</html>