JavaScript实现课堂随机与顺序点名功能

<body>
<form>
  <div align="center">
    <input type="button" value="开始点名" onclick="students()" class="ks"/>
    <input type="button" value="停止点名" onclick="stop()" class="ks" id="nu"/>
    <hr color="blue">
    <br>
    <div id="div1" align="center">随机点名区域</div>
  </div>
</form>
</body>

<script type="text/javascript">
    var i = 0;
    //t用来接收setTimeOut()的返回值
    var t;
    var st = ['张三','李四', '老王','旺财','铁柱', '王八','来福','小明','小红','狗蛋','SB.Child'];
    var u;
    //点名函数
    function students()
    {
      //顺序点名
    /*  if (i < st.length)
      {
        u = st[i];
      }
      else
      {
        //点到最后一个就回来重新点起
        i = 0;
        u = st[i];
      }
      i = i + 1;
*/
      //随机点名 产生0-数组长度之间的数作为数组下标
      var num = Math.floor(Math.random()*st.length);
      u = st[num];
      //更改文本框显示的value值
      document.getElementById("div1").innerHTML = u ;
      t = setTimeout("students()", 1000);
    }
    //停止点名函数
    function stop()
    {
      clearTimeout(t);
    }
    </script>

<style type="text/css">
  body{
    background: #f5faff;
  }
  .ks{
    width: 140px;
    line-height: 55px;
    text-align: center;
    font-weight: bold;
    color: #fff;
    text-shadow:2px 2px 2px #333;
    border-radius: 5px;
    margin:0 20px 20px 0;
    position: relative;
    overflow: hidden;
    background-color: limegreen;
    border:1px solid #d2a000;
    box-shadow: 0 1px 2px #fedd71 inset,0 -1px 0 #a38b39 inset,0 -2px 3px #fedd71 inset;
  }
  #nu{
    background-color: red;
  }
  #div1 { font:40px '微软雅黑';text-align: center; background-color: gainsboro;
    width: 60%;
    height: 60%;
    margin-bottom:20px;
  }
</style>