3.Suspense

等待异步组件时渲染一些额外内容，让应用有更好的用户体验

使用步骤：

异步引入组件

import {defineAsyncComponent} from 'vue'
const Child = defineAsyncComponent(()=>import('./components/Child.vue'))

使用Suspense包裹组件，并配置好default 与 fallback

<template>
	<div class="app">
		<h3>我是App组件</h3>
		<Suspense>
			<template v-slot:default>
				<Child/>
			</template>
			<template v-slot:fallback>
				<h3>加载中.....</h3>
			</template>
		</Suspense>
	</div>
</template>

components

Child.vue

<template>
	<div class="child">
		<h3>我是Child组件</h3>
		{{sum}}
	</div>
</template>

<script>
	import {ref} from 'vue'
	export default {
		name:'Child',
		async setup(){
			let sum = ref(0)
			let p = new Promise((resolve,reject)=>{
				setTimeout(()=>{
					resolve({sum})
				},3000)
			})
			return await p
		}
	}
</script>

<style>
	.child{
		background-color: skyblue;
		padding: 10px;
	}
</style>

App.vue

<template>
	<div class="app">
		<h3>我是App组件</h3>
		<Suspense>
			<template v-slot:default>
				<Child/>
			</template>
			<template v-slot:fallback>
				<h3>稍等，加载中...</h3>
			</template>
		</Suspense>
	</div>
</template>

<script>
	// import Child from './components/Child'//静态引入
	import {defineAsyncComponent} from 'vue' 
	const Child = defineAsyncComponent(()=>import('./components/Child')) //异步引入
	export default {
		name:'App',
		components:{Child},
	}
</script>

<style>
	.app{
		background-color: gray;
		padding: 10px;
	}
</style>

main.js

//引入的不再是Vue构造函数了，引入的是一个名为createApp的工厂函数
import { createApp } from 'vue'
import App from './App.vue'

//创建应用实例对象——app(类似于之前Vue2中的vm，但app比vm更“轻”)
const app = createApp(App)

//挂载
app.mount('#app')