JavaScript 实现简易抽奖程序

<!DOCTYPE html>
<html>
 <head>
 <meta charset="utf-8" />
 <title></title>
 <style>
 #box{
 border: 1px solid aqua;
 height: 100px;
 width: 200px;
 text-align: center;
 line-height: 100px;
 margin: auto;
 font-size: 22px;
 }
 .active{
 background: slateblue;
 }
 li{
 text-align: center;
 list-style:none ;
 width: 40px;
 height: 20px;
 line-height: 20px;
 border: 1px solid blue;
 margin-left: 40px;
 
 float: left;
 }
 ul,li
 {
 list-style: none;
 
 }
 #shu
 {
 margin: auto;
 }
 
 </style>
 </head>
 <body>
 <button id="stp">开始</button><button id="off">停止</button>
 
 <div id="box">恭喜<span>1</span>号 </div>
 <div id="shu">0</div><span>等奖</span>
 <ul>
 <li class="active">1号</li>
 <li>2号</li>
 <li>3号</li>
 <li>4号</li>
 <li>5号</li>
 <li>6号</li>
 <li>7号</li>
 </ul>
 <script>
 var t=null;
 var ostp=document.getElementById("stp");
 var ooff=document.getElementById("off");
 var ospan=document.getElementsByTagName("div")[0].getElementsByTagName("span");
 var oli=document.getElementsByTagName("ul")[0].getElementsByTagName("li");
 var oshu=document.getElementsByClassName("shu");
 function mytime(){
 var n=Math.floor(Math.random()*7+1);
 ospan[0].innerText=n;
 ospan[1].innerText=oli[n-1].innerText;
 for(let i=0;i<oli.length;i++)
 {
 oli[i].className="";
 }
 oli[n-1].className="active";
 }
 function mytime2()
 {
 var a=Math.floor(Math.random()*3+1);
 shu.innerText=a;
 
 
 }
 ostp.onclick=function(){
 clearInterval(t);
 t=setInterval(mytime,50);
 at=setInterval(mytime2,1000)
 }
 ooff.onclick=function(){
 clearInterval(t);
 clearInterval(at);
 }
 </script>
 </body>
</html>