<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="vue.js" type="text/javascript"></script>
    <style type="text/css">
        .active{
            color: red;
        }
    </style>
</head>
<body>
<!--修饰符-->
<div id="app">
    <ul>
        <li v-for="(item ,index) in items" :class="{active:currentIndex===index}" @click="lilick(index)">{{item}}</li>
    </ul>
</div>

<script>
   const app=new Vue({
       el:'#app',
       data:{
          message:"hello" ,
           items:[ "haha",
               'asda',
               'asdfasd',
               'asddddd'],
           currentIndex:-1
       },
       methods:{
           lilick(index){
              this.currentIndex=index;
           }
       }

   })

</script>
</body>
</html>