SOURCE

new Vue({
	el:'#app',
	data:{
		items:['a', 'b', 'c']
	},
	methods:{
		btn(){
			//this.items[1] = 'd'
            this.$set(this.items, 1, 'e')
			console.log(this.items);
		}
	}
})

<div id="app">
	<p v-for="item in items" >{{item}}</p>
	<button @click="btn()">测试</button>
</div>