sabrinaluo

<style>
  img{
    border-radius:10px;
  }
</style>
<img src="xx.jpg">

sabrinaluo

<ul>
  <li>item1</li>
  <li class="active">item2</li>
  <li>item3</li>
</ul>

<script>
  $(ul).find(".active").index(); //return 1
</script>

sabrinaluo

var array = ["lily", "tom", "lucy"];
var ele1 = "lily";
var ele2 = "lucy";
var ele3 = "jack";

array.indexOf(ele1); // return 0
array.indexOf(ele2); // return 2

array.indexOf(ele3); //return -1; NOTE: element is not in the array if return -1