通过时间事件创建一个始终。 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>蜜蜂教程(mifengjc.com)</title>
  <script>
    function startTime() {
      var today = new Date();
      var h = today.getHours();
      var m = today.getMinutes();
      var s = today.getSeconds(); // 在小于10的数字钱前加一个‘0’
      m = checkTime(m);
      s = checkTime(s);
      document.getElementById('txt').innerHTML = h + ":" + m + ":" + s;
      t = setTimeout(function() {
        startTime()
      }, 500);
    }

    function checkTime(i) {
      if (i < 10) {
        i = "0" + i;
      }
      return i;
    }
  </script>
</head>
<body onload="startTime()">

  <div id="txt"></div>

</body>
</html>
        