js点击抽奖功能

<div align="center">
    <div id="d"></div>
    <div  id="d1">
        <br>
        <label id="a">&nbsp</label>
    </div>
    <div>
        <br>
        <input type="button" onclick="sleep()" value="开始">
        //空格
        &nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp 
        <input type="button" id="i2" value="结束">
    </div>
</div>

 var a=document.getElementById("a");
    var i2=document.getElementById("i2");
    let name;
    let l=["111","123","564","999","954","654","365","211","911","778","698","365","468","777","831","126"]; 
    // alert(l.length);
    //a.innerHTML=l[Math.round(Math.random()*(l.length-1))];
    function sleep(){
        flag=true;  //设置标志,判断停止时间
        setTimeout(change,50);  //随机跳动,延时50毫秒
    }  
    i2.onclick=function(){
    flag=false;  //结束标志
    }
    function change(){
        name = l[Math.floor(Math.random()*l.length)]; //随机取值
        console.log(name);
        if(!flag){
            a.innerHTML=name;
        }else{
            a.innerHTML=name;
            sleep();  //迭代  
        }
    }