以前(Vue2.x)

import Vue from 'vue'import App from './App.vue'Vue.config.ignoredElements = [/^app-/]Vue.use(/* ... */)Vue.mixin(/* ... */)Vue.component(/* ... */)Vue.directive(/* ... */)new Vue({ render: h => h(App)}).$mount('#app')

当前(Vue3.0)

import { createApp } from 'vue'import App from './App.vue'const app = createApp(App)app.config.ignoredElements = [/^app-/]app.use(/* ... */)app.mixin(/* ... */)app.component(/* ... */)app.directive(/* ... */)app.mount('#app')

新全局API

import { createApp } from 'vue'import App from './App.vue'const app = createApp(App)

全局映射API

1.全局配置

Vue.config -> app.config

2.注册类型API

Vue.component -> app.componentVue.directive -> app.directiveVue.filter -> app.filter

3.扩展类型API

Vue.mixin -> app.mixinVue.use -> app.use

手动挂载

const rootInstance = app.mount('#app')rootInstance instanceof Vue // true

也可以接受第二参数props

app.mount('#app', { // props to be passed to root component})

依赖注册

// in the entryapp.provide({ [ThemeSymbol]: theme})// in a child componentexport default { inject: { theme: { from: ThemeSymbol } }, template: `

缺陷

Vue2.x中，许多库和插件在UMD构建的时候是自动安装的，如路由vue-router：

自动安装的时候会调用Vue.use(),在上述“扩展类型API”已表明，Vue.use()修正为实例app.use()，Vue.use已不再使用，当然会提供预警信息。