[Vue warn]: Property or method "currentIndex" is not defined on the instance but referenced during render.

<div v-for="(item,index) in title" @click="tabClick(index)" class="tab-control-item" :class="{active:index === currentIndex}">
      <span>{{item}}</span>
    </div>

        methods:{
    tabClick(index){
      console.log(index)
      this.currentIndex=this.index
    }
  }

currentIndex没有再data里定义