<template>
<div class="wrap" :style="{height:hHeight+'px'}">
</div>
</template>
<script lang='ts'>
import { defineComponent, reactive, nextTick, onMounted, toRefs } from "vue";
export default defineComponent({
  name: "Aboutus",
  setup() {
    let state = reactive({
      hHeight: 0,//頁面高度
    });
  onMounted(() => {
    nextTick(()=>{
        state.hHeight = document.documentElement.clientHeight;
        console.log(document.documentElement.clientHeight)
    })
  })
  return {
      ...toRefs(state)
  }
  },
});
</script>

用vue3.2版本的也可以用語法糖來處理，直接上代碼：

<template>
  <div class="wrap" :style="{height:state.hHeight+'px'}">
   </div>
</template>
<script setup>
import { reactive, nextTick } from "vue"
const state = reactive({
    hHeight: 0
})
nextTick(()=>{
     state.hHeight = document.documentElement.clientHeight;
     console.log(document.documentElement.clientHeight)
 })
</script>

親測可用，大家可以試試！

vue3之vue3.2獲取dom元素的寬高

知識點：ref，nextTike

ref可以用于dom對象的獲取，以及創(chuàng)建一個響應(yīng)式的普通對象類型
nextTick是一個函數(shù)，它接受一個函數(shù)作為參數(shù)，nextTick官網(wǎng)定義是‘將回調(diào)推遲到下一個 DOM 更新周期之后執(zhí)行’，

未使用nextTike

<!--
 * new page
 * @author: Blaine
 * @since: 2022-06-30
 * page_nextTike.vue
-->
<template>
  <div class="container" >
    <ul ref="myRef">
      <li v-for="(item, index) in pepleList" :key="index">{{ item }}</li>
    </ul>
    <button @click="addHandle">增加</button>
  </div>
</template>

<script setup lang="ts">
import { onMounted, reactive, ref, nextTick } from 'vue'
let pepleList = reactive<string[]>(['蜘蛛俠', '鋼鐵俠', '美國隊長'])
const myRef = ref<HTMLElement>();
onMounted(() => {
  console.log('列表的高度是：', myRef.value?.clientHeight)
})
const addHandle =  async() => {
  pepleList.push('閃電俠')
  // await nextTick()
  console.log('列表的高度是：', myRef.value?.clientHeight)
}
</script>

<style scoped>
</style>

**注意：**這里的list并沒有立即增加

問題在于我們改變list的值時，vue并不是立刻去更新dom，而是在一個事件循環(huán)最后再去更新dom，這樣可以避免不必要的計算和dom操作，對提高性能非常重要。

那么我們需要在dom更新完成后，再去獲取ul的高度，這時候就需要用到nextTick了，

使用ref+nextTick

<!--
 * new page
 * @author: Blaine
 * @since: 2022-06-30
 * page_nextTike.vue
-->
<template>
  <div class="container" >
    <ul ref="myRef">
      <li v-for="(item, index) in pepleList" :key="index">{{ item }}</li>
    </ul>
    <button @click="addHandle">增加</button>
  </div>
</template>

<script setup lang="ts">
import { onMounted, reactive, ref, nextTick } from 'vue'
let pepleList = reactive<string[]>(['蜘蛛俠', '鋼鐵俠', '美國隊長'])
const myRef = ref<HTMLElement>();
onMounted(() => {
  console.log('列表的高度是：', myRef.value?.clientHeight)
})
const addHandle =  async() => {
  pepleList.push('閃電俠')
  await nextTick()
  console.log('列表的高度是：', myRef.value?.clientHeight)
}
</script>

<style scoped>
</style>