css点名

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title></title>
</head>
<body>
  <h2>点击到的名字：<span></span></h2>
  <button >开始点名</button>
</body>
<script type="text/javascript">
  var arr=["崔星宇","刘子煜","陈琪","泊然","王世麒"]
  var btn=document.querySelector("button");
  var span=document.querySelector("span");
  var clock;
  btn.onclick=function(){
   if(btn.innerHTML=="开始点名")
   {
    clock=setInterval(function(){
    var a=parseInt(Math.random()*4);
    span.innerHTML=arr[a];
    },100)
    btn.innerHTML="结束点名"
   }
   else{
    clearInterval(clock);
    btn.innerHTML="开始点名";
   }



  }
</script>
</html>