vue3使用nextTick

1. 发现nextTick必须放在修改一个响应式数据之后，才会在onUpdated之后被调用，如果nextTick是放在所有对响应式数据修改之前，则nextTick里面的回调函数会在onBeforeUpdate方法执行前就被调用了。可是nextTick必须等到onUpdated执行完成之后执行，才能拿到渲染得到的dom
2. 下面发请求的时候是没有使用async的(Promise的语法糖)，它里面的then函数对serverRef的修改，会再一次触发组件重新渲染，也就是onBeforeUpdate和onUpdated又被回调了一次，也就是说，下面的toggleColor这个方法，触发了2次渲染。

---onBeforeMounted---
RefImpl {__v_isShallow: false, dep: undefined, __v_isRef: true, _rawValue: null, _value: null}
---mounted---
RefImpl {__v_isShallow: false, dep: undefined, __v_isRef: true, _rawValue: span, _value: span}
halo world
---onBeforeUpdate---
---onUpdated---
RefImpl {__v_isShallow: false, dep: undefined, __v_isRef: true, _rawValue: button, _value: button}
nextTick1
res ojbk
---onBeforeUpdate---
---onUpdated---
nextTick2

<template><div style="display: flex;"><ul class="ul-list"><li v-for="i in num" :id="'li'+i" >{{ i }}</li></ul><div class="div-desc"><input type="text" v-model="n"><button @click="handleClick">修改num</button><br><br><button @click="toggleColor">切换span颜色</button><span ref="spanRef" :style="{color:colorRef}">span</span>*{{ serverResp }}*<button v-if="isShow" ref="btnRef">dd</button></div></div></template><script lang="ts" setup>import { ref,reactive,onBeforeMount,onMounted,onBeforeUpdate,onUpdated,nextTick,getCurrentInstance } from 'vue'const { proxy } = getCurrentInstance()let num = ref(10)let n = ref(10)const btnRef = ref(null)let isShow = ref(false)let serverResp = ref('')const spanRef = ref(null)const handleClick = () => {num.value = parseInt(n.value)}const colorRef = ref('')const toggleColor = () => {debuggerproxy.Request({url:'http://localhost:8083/test'}).then(res=>{debuggerconsole.log('res',res);serverResp.value = resnextTick(()=>{ // 要放在对响应式数据修改之后debuggerconsole.log('nextTick2');})})debuggerisShow.value = truenextTick(()=>{  // 要放在对（至少一个）响应式数据修改之后，// 否则这里函数调用将拿不到btnRef,必须要等到onUpdated回调之后，执行nextTick里面的回调才能拿到btnRefdebuggerconsole.log(btnRef); console.log('nextTick1');})if(colorRef.value === 'red') {colorRef.value = 'blue'} else {colorRef.value = 'red'}num.value = num.value - 1debuggerconsole.log('halo world');}onBeforeMount(() => {console.log('---onBeforeMounted---')console.log(spanRef);})onMounted(()=>{console.log('---mounted---')console.log(spanRef);spanRef.value.style.color = 'cyan'}) onBeforeUpdate(()=>{debuggerconsole.log('---onBeforeUpdate---')})onUpdated(()=>{debuggerconsole.log('---onUpdated---')})</script><style lang="scss">.ul-list {width: 100px;}.div-list { width: 300px;}
</style>