JS实现随机点名器

<div id="dv">
 <input type="button" value="开始点名" id="btu">
 <input type="button" value="停止" id="btu1">
 <div class="luc">你将会是下一个幸运儿吗？请看大屏幕</div>
 <div class="ch">
 <span class="name"></span>
 </div>
</div>

*{
 margin: 0px;
 padding: 0px;
}
body{
 background-color: cornsilk;
}
#dv{
 width: 800px;
 margin: 20px auto;
 border: 4px solid darkviolet;
 text-align: center;
}
ul li{
 vertical-align: top;
 display: inline-block;
 width: 100px;
 height: 50px;
 border-radius: 35%;
 border: 3px dashed palevioletred;
 text-align: center;
 line-height: 50px;
 margin: 5px 5px;
}
li.change{
 background-color: greenyellow;
 font-size: 15px;
 color: black;
 font-weight: bolder;
}
#btu,#btu1{
 width: 100px;
 height: 50px;
 font-size: 15px;
 border-radius: 10px;
 cursor: pointer;
 margin: 10px 50px 0 50px;
 color: brown;
 background-color: pink;
}
.ch{
 position: relative;
 width: 150px;
 height: 150px;
 border-radius: 10px;
 margin: 12px auto;
 border: 2px solid yellow;
}
.luc{
 font-size: 20px;
 font-weight: bold;
 margin: 10px auto;
 text-align: center;
 color: green;
}
.name{
 position: absolute;
 font-size: 35px;
 left: 40px;
 top: 50px;
}

//获取dv元素
var dv=document.getElementById("dv");
//获取点击开始按钮
var btu=document.getElementById("btu");
//获取点击结束按钮
var btu1=document.getElementById("btu1");

//创建ul列表
var ula=document.createElement("ul");
//将ul追加到父级元素div中
dv.appendChild(ula);
//获取js中插入的Li标签；
var oLi=document.getElementsByTagName("li");
//插入数组
var arr=["01","02","03","04","05","06","07","08","09","10","11","12","13","14","15","16","17","18","19","20","21","22","23"]
//动态创建li，追加到ul
for(var i=0;i<arr.length;i++){
 //创建li标签
 var liObj=document.createElement("li");
 liObj.innerText=arr[i];
 ula.appendChild(liObj);
}

//声明timer
var timer = null;
//点击开始进行随机选择
btu.onclick=function () {
 //每次运行之前清除timer;
 clearInterval(timer);
 //设置定时器
 timer=setInterval(function () {
  //根据数组长度范围生成随机数
  var i = Math.floor(Math.random()*arr.length);
  //通过for循环清空所有class类样式
  for(var j=0;j<oLi.length;j++){
   oLi[j].removeAttribute("class");
  }
  //为随机选择的li重新设置类样式
  oLi[i].className="change";
 },50);
};

btu1.onclick=function () {
 //清除timer;
 clearInterval(timer);
 //根据类样式找到选中的元素
 var choise = document.getElementsByClassName("change")[0];
 //获取选中元素的内容
 var name=choise.innerText;
 //获取选中展示位置
 var nameSpan = document.getElementsByClassName('name')[0];
 //位置添加内容
 nameSpan.innerText=name+"号";
}