原生js实现随机点餐效果

<div class="wrap">
    <div id="box">    
</div>
<button id="start">开始</button>
<button id="s">停止</button>

.wrap{
    width: 500px;
    height: 400px;
    margin: 0 auto;
    text-align: center;
}
#box{
    width: 100%;
    height: 300px;
    border: 1px solid red;      
    text-align: center;
    line-height: 300px;
    font-size: 30px;
    margin-bottom: 20px;
}

var arr = ['宫保鸡丁', '糖醋里脊', '红烧带鱼', '牛腩煲', '红烧肉'];
var start = document.getElementById("start"),
      s = document.getElementById("s"),
      box = document.getElementById("box"),
      timer = null;

start.onclick = function(){  
   timer = setInterval(function(){
      var index = Math.floor(Math.random()arr.length);
      box.innerHTML = arr[index];
    }, 100)      
}
s.onclick = function(){
      clearInterval(timer);
}