18：vue3 异步加载

在大型项目中，我们可能需要拆分应用为更小的块，并仅在需要时再从服务器加载相关组件。Vue 提供了 defineAsyncComponent 方法来实现此功能：

 1 <template>
 2   <h3>异步加载</h3>
 3   <KeepAlive>
 4     <component :is="tabComponent"></component>
 5   </KeepAlive>
 6   <button @click="changeHandle">切换组件</button>
 7 </template>
 8 
 9 <script>
10 
11 import { defineAsyncComponent } from "vue"
12 import ComponentA from "./components/ComponentA.vue"
13 const  AsyncComponentB =defineAsyncComponent (()=>
14   import('./components/ComponentB.vue')
15 )
16 
17 export default{
18     data(){
19       return{
20         tabComponent:"ComponentA"
21       }
22     },
23     methods:{
24       changeHandle(){
25         this.tabComponent=this.tabComponent=="ComponentA"?"AsyncComponentB":"ComponentA"
26       }
27    },
28    components:{
29     ComponentA,
30     AsyncComponentB
31    }
32     
33 }
34 </script>

切换组件时，网络请求会加载B