feat: add createApp

README.md

@@ -369,6 +369,27 @@ watch(() => {
 
 </details>
 
+### createApp
+
+<details>
+<summary>
+⚠️ <code>createApp()</code> is global
+</summary>
+
+In Vue 3, `createApp()` is introduced to provide context(plugin, components, etc.) isolation between app instances. Due the the design of Vue 2, in this plugin, we provide `createApp()` as a forward compatible API which is just an alias of the global.
+
+```ts
+const app1 = createApp(RootComponent1)
+app1.component('Foo', Foo) // equivalent to Vue.component('Foo', Foo)
+app1.use(VueRouter) // equivalent to Vue.use(VueRouter)
+
+const app2 = createApp(RootComponent2)
+app2.component('Bar', Bar) // equivalent to Vue.use('Bar', Bar)
+```
+
+</details>
+
+
 ### Missing APIs
 
 The following APIs introduced in Vue 3 are not available in this plugin.

src/createApp.ts

@@ -0,0 +1,53 @@
+import type Vue from 'vue'
+import { VueConstructor } from 'vue/types/umd'
+import { getCurrentVue } from './runtimeContext'
+import { warn } from './utils'
+
+export interface App {
+  config: VueConstructor['config']
+  use: VueConstructor['use']
+  mixin: VueConstructor['mixin']
+  component: VueConstructor['component']
+  directive: VueConstructor['directive']
+  mount: Vue['$mount']
+  unmount: Vue['$destroy']
+}
+
+export function createApp(rootComponent: any, rootProps: any = undefined): App {
+  const V = getCurrentVue()!
+
+  let mountedVM: Vue | undefined = undefined
+
+  return {
+    config: V.config,
+    use: V.use.bind(V),
+    mixin: V.mixin.bind(V),
+    component: V.component.bind(V),
+    directive: V.directive.bind(V),
+    mount: (el, hydrating) => {
+      if (!mountedVM) {
+        mountedVM = new V({ propsData: rootProps, ...rootComponent })
+        mountedVM.$mount(el, hydrating)
+        return mountedVM
+      } else {
+        if (__DEV__) {
+          warn(
+            `App has already been mounted.\n` +
+              `If you want to remount the same app, move your app creation logic ` +
+              `into a factory function and create fresh app instances for each ` +
+              `mount - e.g. \`const createMyApp = () => createApp(App)\``
+          )
+        }
+        return mountedVM
+      }
+    },
+    unmount: () => {
+      if (mountedVM) {
+        mountedVM.$destroy()
+        mountedVM = undefined
+      } else if (__DEV__) {
+        warn(`Cannot unmount an app that is not mounted.`)
+      }
+    },
+  }
+}

src/index.ts

@@ -14,6 +14,7 @@ const VueCompositionAPI = {
 }
 
 export default VueCompositionAPI
+export { createApp } from './createApp'
 export { nextTick } from './nextTick'
 export { createElement as h } from './createElement'
 export { getCurrentInstance } from './runtimeContext'

test/createApp.spec.js

@@ -0,0 +1,66 @@
+const Vue = require('vue/dist/vue.common.js')
+const { createApp, defineComponent, ref, h } = require('../src')
+
+describe('createApp', () => {
+  it('should work', async () => {
+    const vm = new Vue({
+      setup() {
+        return {
+          a: ref(1),
+        }
+      },
+      template: '<p>{{a}}</p>',
+    }).$mount()
+
+    await Vue.nextTick()
+    expect(vm.a).toBe(1)
+    expect(vm.$el.textContent).toBe('1')
+  })
+
+  it('should work with rootProps', async () => {
+    const app = createApp(
+      defineComponent({
+        props: {
+          msg: String,
+        },
+        template: '<p>{{msg}}</p>',
+      }),
+      {
+        msg: 'foobar',
+      }
+    )
+    const vm = app.mount()
+
+    await Vue.nextTick()
+    expect(vm.$el.textContent).toBe('foobar')
+  })
+
+  it('should work with components', async () => {
+    const Foo = defineComponent({
+      props: {
+        msg: {
+          type: String,
+          required: true,
+        },
+      },
+      template: '<p>{{msg}}</p>',
+    })
+
+    const app = createApp(
+      defineComponent({
+        props: {
+          msg: String,
+        },
+        template: '<Foo :msg="msg"/>',
+      }),
+      {
+        msg: 'foobar',
+      }
+    )
+    app.component('Foo', Foo)
+    const vm = app.mount()
+
+    await Vue.nextTick()
+    expect(vm.$el.textContent).toBe('foobar')
+  })
+})