JavaScript实现随机点名网页

<!DOCTYPE html>
<html>
 <head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>
   * {
    margin: 0;
    padding: 0;
   }
   #box {
    border: 1px solid black;/*设置盒子的边框和颜色*/
    width: 500px;
    height: 500px;
    margin: 100px auto;/*离顶部200px，并且居中*/
    background-color: #000000;/*盒子的背景颜色*/
    position: relative;/*定位*/
   }
   p{
    width: 500px;
    height: 200px;
    text-align: center;/*将文本居中*/
    line-height: 200px;/*设置行高*/
    font-size: 80px;/*字体大小*/
    color: #ffff00;
   }
   #anniu {
    width: 200px;
    height: 50px;
    background-color:#00aaff;
    position: absolute;
    bottom: 100px;/*距离底部100px*/
    left: 50%;
    margin-left: -100px;
    color: #ffffff;
    font-size: 20px
   }
  </style>
 </head>
 <body>
  <div id="box">
   <p id="wenben">随机点名册</p>
   <input type="button" value="开始点名" id="anniu">
  </div>
 </body>
 <script>
  var wenben = document.getElementById("wenben")
  var anniu = document.getElementById("anniu")
  var timer //定义计时器            
  var arr = ['刘一','陈二','张三','李四','王五','赵六','孙七','周八','吴九','郑十']
  var test = true
  anniu.onclick = function() {
   if (test) {
    start()
    anniu.innerHTML = "结束"
    test = false
   } else {
    stop()
    anniu.innerHTML = "开始"
    test = true
   }
  }
  function start() { /*开始*/
   timer = setInterval(function random() {
    var index = parseInt(Math.random() * arr.length)
    wenben.innerHTML = arr[index]
   }, 50);
  }
  function stop() { /*结束*/
   clearInterval(timer)
  }
 </script>
</html>