<template>
  <div class="main">
    <div
      class="aaa"
      :class="{active:index==isActive}"
      v-for="(item, index) in contentlist"
      @click="showdifference(index)"
      :key="index">
      {{item.key}}
    </div>
  </div>
</template>
<script>
export default {
  data() {
    return {
      isActive: '',
      contentlist: [{key: 1}, {key: 2}, {key: 3}, {key: 4}]
    }
  },
  methods: {
    showdifference(index){
      this.isActive = index
      console.log(this.isActive)
    }
  }
}
</script>
<style>
.aaa {
  margin: 10px;
  width: 95%;
  height: 100px;
  border: 1px solid;
}
.active{
  border: 2px solid red;
}
</style>