SOURCE

var vm = new Vue({
    el: '#app',
    data: {
        items: [
            { id: 1, msg: 'hello' },
            { id: 2, msg: 'world' }
        ]
    },
    mounted() {
        document.getElementById('noKey').nextElementSibling.style.color = 'red';
        document.getElementById('hasKey').nextElementSibling.style.color = 'red';
    },
    methods: {
        reverse: function () {
            let newArr = []
            newArr = this.items.reverse()
            this.items = newArr
        }
    }
})

    <div id="app">
        <span id="noKey">没有key</span>
        <div v-for="item in items">
            {{item.msg}}
        </div>
        <span id="hasKey">添加key</span>
        <div v-for="item in items" :key="item.id">
            {{item.msg}}
        </div>
        <button @click="reverse">changeBtn</button>
    </div>

body {
    font-size: 24px
}