JavaScript 实时时钟实现代码详解

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="gb2312">
  <title>Document</title>
  <script type="text/javascript">

    function startTime () {
       var today=new Date();
    var y=today.getFullYear();
    var mon=today.getMonth()+1;
       mon=changNum(mon);
    var d=today.getDay();
       d=changNum(d);
    var h=today.getHours();
    var m=today.getMinutes();
       m=changNum(m);
    var s=today.getSeconds();
       s=changNum(s);
    document.getElementById("timeid").innerHTML=y+"年"+mon+"月"+d+"日"+h+":"+m+":"+s;
    t=setTimeout(function(){
      startTime();
    },500);
    }    

   function changNum(i){   //月、日、秒如果小于10数字前加0
       if(i<10){
          return "0"+i;
       }
       return i;
   }

  </script>
</head>
<body onload="startTime()">

<h1 id="timeid"></h1>

</body>
</html>