vue中的$nextTick

<template>
    <div>
        <ul>
            <li v-for="item in list1">{{item}}</li>
        </ul>
        <ul>
            <li v-for="item in list2">{{item}}</li>
        </ul>
        <ol>
            <li v-for="item in list3">{{item}}</li>
        </ol>
        <ol>
            <li v-for="item in list4">{{item}}</li>
        </ol>
        <ol>
            <li v-for="item in list5">{{item}}</li>
        </ol>
    </div>
</template>
<script type="text/javascript">
export default {
    data() {
        return {
            list1: [],
            list2: [],
            list3: [],
            list4: [],
            list5: []
        }
    },
    created() {
        this.composeList12()
        this.composeList34()
        this.composeList5()
        this.$nextTick(function() {
            // DOM 更新了
            console.log('finished test ' + new Date().toString())
            console.log(document.querySelectorAll('li').length)
        })
    },
    methods: {
        composeList12() {
            let me = this
            let count = 10000

            for (let i = 0; i < count; i++) {
                Vue.set(me.list1, i, 'I am a 测试信息～～啦啦啦' + i)
            }
            console.log('finished list1 ' + new Date().toString())

            for (let i = 0; i < count; i++) {
                Vue.set(me.list2, i, 'I am a 测试信息～～啦啦啦' + i)
            }
            console.log('finished list2 ' + new Date().toString())

            this.$nextTick(function() {
                // DOM 更新了
                console.log('finished tick1&2 ' + new Date().toString())
                console.log(document.querySelectorAll('li').length)
            })
        },
        composeList34() {
            let me = this
            let count = 10000

            for (let i = 0; i < count; i++) {
                Vue.set(me.list3, i, 'I am a 测试信息～～啦啦啦' + i)
            }
            console.log('finished list3 ' + new Date().toString())

            this.$nextTick(function() {
                // DOM 更新了
                console.log('finished tick3 ' + new Date().toString())
                console.log(document.querySelectorAll('li').length)
            })

            setTimeout(me.setTimeout1, 0)
        },
        setTimeout1() {
            let me = this
            let count = 10000

            for (let i = 0; i < count; i++) {
                Vue.set(me.list4, i, 'I am a 测试信息～～啦啦啦' + i)
            }
            console.log('finished list4 ' + new Date().toString())

            me.$nextTick(function() {
                // DOM 更新了
                console.log('finished tick4 ' + new Date().toString())
                console.log(document.querySelectorAll('li').length)
            })
        },
        composeList5() {
            let me = this
            let count = 10000

            this.$nextTick(function() {
                // DOM 更新了
                console.log('finished tick5-1 ' + new Date().toString())
                console.log(document.querySelectorAll('li').length)
            })

            setTimeout(me.setTimeout2, 0)
        },
        setTimeout2() {
            let me = this
            let count = 10000

            for (let i = 0; i < count; i++) {
                Vue.set(me.list5, i, 'I am a 测试信息～～啦啦啦' + i)
            }
            console.log('finished list5 ' + new Date().toString())

            me.$nextTick(function() {
                // DOM 更新了
                console.log('finished tick5 ' + new Date().toString())
                console.log(document.querySelectorAll('li').length)
            })
        }
    }
}</script>

以上代码的输出结果为：

finish list1
finish list2
finish list3
finish tick1&2
30000
finish tick3
30000
finish tick5-1
40000 
finish test
50000

由上述可以得到以下结论：

1. 在同一事件循环中，只有当数据全部更新完毕后，才会执行nextTick（由先输出list1/2/3后，才输出tick数据得出）

2. 仅在同步环境中的数据完全更新完毕后，才会渲染DOM，显示页面（在setTimeout的回调执行之前，输出的li的长度都为30000）

3. 在同一事件循环中，nextTick会按照顺序执行

4. 只有同步环境执行完，且DOM渲染完毕后，才会执行异步任务的callback（由先输出list3后输出tick1&2得出）