                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /JavaScript进阶篇

为什么不可以执行？

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>计时器</title>
<script type="text/javascript">
   var i;
   function clock(){
      var time=new Date();
      document.getElementById("clock").value = time;
   }
    i =setInterval("clock()",1000);
    function continue(){
    i=setInterval("clock()",1000);
    }
</script>
</head>
<body>
<form>
    <input type="text" id="clock" size="50" />
    <input type="button" value="Stop" onclick="clearInterval(i)"/>
    <input type="button" value="start" onclick="continue()">
</form>
</body>
</html>