vue单条刷新采坑

<template>
	<div v-for="item in list">
            <div>
                <button @click="changeItem(item)">更改{{item.arr}}</button>
            </div>
            <div v-for="i in item.arr" >
                {{i.a}}
            </div>
            <hr>
    </div>
</template>  
<script>
    export default {
        data(){
            return {
                list: [
                    {
                        arr: [
                            {a:1},
                            {a:2}
                        ]
                    }
                ]
            }
        },
        methods:{
            changeItem(item){
                console.log(item,this.list[0],item===this.list[0])
                // 就是这个地方巨坑
                /*item = {
                    arr: [

                    ]
                }*/
                let obj = {
                    arr: [
                    ]
                }
                // this.$set(this.list,0,obj)
                item = Object.assign(item, obj)
                console.log(item,this.list[0],item===this.list[0])
            },
        }
    }
</script>