JavaScript实现随机点名程序

<script>
var arr = ["唐僧", "孙悟空", "猪八戒", "沙悟净", "白骨精", "玉皇大帝", "红孩儿", "白骨精", "太上老君"]

var myTimer = null //定时器编号

// 既是启动定时器的函数，也是停止定时器的函数
function goAndStop(){
 // 如果当前没有定时器在执行，则启动，否则，停止定时器；
 if(myTimer == null){
  // 启动定时器，随机下标，取出名字
  myTimer = setInterval(function(){
   // 1、随机下标
   var index = parseInt(Math.random()*arr.length)

   // 2、根据下标取出学生的姓名，显示在页面上
   document.getElementById("stuName").innerHTML = arr[index]

  },10);

  //启动定时器的同时，改变按钮状态，为下次单击做准备
  document.getElementById("btn").value = "停 止"
 }else{
  // 当前若有有定时器在执行，则停止定时器, 恢复初始状态
  window.clearInterval(myTimer)
  myTimer = null
  document.getElementById("btn").value = "开 始"
 }
}
</script>

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <meta http-equiv="X-UA-Compatible" content="ie=edge">
 <title>Document</title>
 <style>
 #box{
  width:200px;
  height: 300px;
  margin: 100px auto;
 }

 #stuName{
  width: 100%;
  height: 80px;
  border: 2px solid gray;
  line-height: 80px;
  text-align: center;
  font-size: 30px;
  color:orange;
  font-weight: bold;
 }

 input{
  margin-top:30px;
  width: 100%;
  height: 50px;
  font-size: 20px;
  font-weight: bold;
 }

 </style>
</head>
<body>
 <div id="box">
  <div id="stuName">
   随机名单
  </div>
  <input id="btn" type="button" value="开 始" onclick="goAndStop()">
 </div>
</body>
</html>
<script>
var arr = ["唐僧", "孙悟空", "猪八戒", "沙悟净", "白骨精", "玉皇大帝", "红孩儿", "白骨精", "太上老君"]

var myTimer = null 
function goAndStop(){
 if(myTimer == null){
  myTimer = setInterval(function(){
   var index = parseInt(Math.random()*arr.length)

   document.getElementById("stuName").innerHTML = arr[index]

  },10);
  document.getElementById("btn").value = "停 止"
 }else{
  window.clearInterval(myTimer)
  myTimer = null
  document.getElementById("btn").value = "开 始"
 }
}
</script>