JS练习开关灯

<style type="text/css">
  html,body{
         margin: 0;
        padding: 0;;
      cursor: pointer;
       100%;
      height: 100%;
    }
</style>



<body id="ids">
<script type="text/javascript">
    console.log("开始");
   var did =document.getElementById("ids");
      did.onclick = function(){
          console.log("sad");
            var bg =this.style.backgroundColor;

            switch (bg){
                case "white" :
                    this.style.backgroundColor = "blue";
                    break;
                case "blue" :
                    this.style.backgroundColor = "red";
                    break;
                case "red" :
                    this.style.backgroundColor ="yellow";
                    break;
                case "yellow" :
                    this.style.backgroundColor = "black";
                    break;
                default:  this.style.backgroundColor ="white";
        }
          }
</script>
</body>