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# @vue/composition-api
Vue 2 plugin for **Composition API**
[![npm](https://img.shields.io/npm/v/@vue/composition-api)](https://www.npmjs.com/package/@vue/composition-api)
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English | [中文](./README.zh-CN.md) ・ [**Composition API Docs**](https://v3.vuejs.org/guide/composition-api-introduction.html)
> ⚠️ With the release of [Vue 2.7](https://blog.vuejs.org/posts/vue-2-7-naruto.html), which has Composition API built-in, **you no longer need this plugin**. Thereby this plugin has entered maintenance mode and will only support Vue 2.6 or earlier. This project will reach End of Life by the end of 2022.
## Installation
### NPM
```bash
npm install @vue/composition-api
# or
yarn add @vue/composition-api
```
You must install `@vue/composition-api` as a plugin via `Vue.use()` before you can use the [Composition API](https://composition-api.vuejs.org/) to compose your component.
```js
import Vue from 'vue'
import VueCompositionAPI from '@vue/composition-api'
Vue.use(VueCompositionAPI)
```
```js
// use the APIs
import { ref, reactive } from '@vue/composition-api'
```
> :bulb: When you migrate to Vue 3, just replacing `@vue/composition-api` to `vue` and your code should just work.
### CDN
Include `@vue/composition-api` after Vue and it will install itself automatically.
<!--cdn-links-start-->
```html
<script src="https://cdn.jsdelivr.net/npm/vue@2.6"></script>
<script src="https://cdn.jsdelivr.net/npm/@vue/composition-api@1.7.2"></script>
```
<!--cdn-links-end-->
`@vue/composition-api` will be exposed to global variable `window.VueCompositionAPI`.
```ts
const { ref, reactive } = VueCompositionAPI
```
## TypeScript Support
> TypeScript version **>4.2** is required
To let TypeScript properly infer types inside Vue component options, you need to define components with `defineComponent`
```ts
import { defineComponent } from '@vue/composition-api'
export default defineComponent({
// type inference enabled
})
```
### JSX/TSX
JSX is now officially supported on [vuejs/jsx](https://github.com/vuejs/jsx). You can enable it by following [this document](https://github.com/vuejs/jsx/tree/dev/packages/babel-preset-jsx#usage). A community maintained version can be found at [babel-preset-vca-jsx](https://github.com/luwanquan/babel-preset-vca-jsx) by [@luwanquan](https://github.com/luwanquan).
To support TSX, create a declaration file with the following content in your project.
```ts
// file: shim-tsx.d.ts
import Vue, { VNode } from 'vue';
import { ComponentRenderProxy } from '@vue/composition-api';
declare global {
namespace JSX {
interface Element extends VNode {}
interface ElementClass extends ComponentRenderProxy {}
interface ElementAttributesProperty {
$props: any; // specify the property name to use
}
interface IntrinsicElements {
[elem: string]: any;
}
}
}
```
## SSR
Even if there is no definitive Vue 3 API for SSR yet, this plugin implements the `onServerPrefetch` lifecycle hook that allows you to use the `serverPrefetch` hook found in the classic API.
```js
import { onServerPrefetch } from '@vue/composition-api'
export default {
setup(props, { ssrContext }) {
const result = ref()
onServerPrefetch(async () => {
result.value = await callApi(ssrContext.someId)
})
return {
result,
}
}
}
```
## Browser Compatibility
`@vue/composition-api` supports all modern browsers and IE11+. For lower versions IE you should install `WeakMap` polyfill (for example from `core-js` package).
## Limitations
> :white_check_mark: Support &nbsp;&nbsp;&nbsp;&nbsp;:x: Not Supported
### `Ref` Unwrap
<details>
<summary>
❌ <b>Should NOT</b> use <code>ref</code> in a plain object when working with <code>Array</code>
</summary>
```js
const a = {
count: ref(0),
}
const b = reactive({
list: [a], // `a.count` will not unwrap!!
})
// no unwrap for `count`, `.value` is required
b.list[0].count.value === 0 // true
```
```js
const b = reactive({
list: [
{
count: ref(0), // no unwrap!!
},
],
})
// no unwrap for `count`, `.value` is required
b.list[0].count.value === 0 // true
```
</details>
<details>
<summary>
✅ <b>Should</b> always use <code>ref</code> in a <code>reactive</code> when working with <code>Array</code>
</summary>
```js
const a = reactive({
list: [
reactive({
count: ref(0),
}),
]
})
// unwrapped
a.list[0].count === 0 // true
a.list.push(
reactive({
count: ref(1),
})
)
// unwrapped
a.list[1].count === 1 // true
```
</details>
### Template Refs
<details>
<summary>
✅ String ref && return it from <code>setup()</code>
</summary>
```html
<template>
<div ref="root"></div>
</template>
<script>
export default {
setup() {
const root = ref(null)
onMounted(() => {
// the DOM element will be assigned to the ref after initial render
console.log(root.value) // <div/>
})
return {
root,
}
},
}
</script>
```
</details>
<details>
<summary>
✅ String ref && return it from <code>setup()</code> && Render Function / JSX
</summary>
```jsx
export default {
setup() {
const root = ref(null)
onMounted(() => {
// the DOM element will be assigned to the ref after initial render
console.log(root.value) // <div/>
})
return {
root,
}
},
render() {
// with JSX
return () => <div ref="root" />
},
}
```
</details>
<details>
<summary>
❌ Function ref
</summary>
```html
<template>
<div :ref="el => root = el"></div>
</template>
<script>
export default {
setup() {
const root = ref(null)
return {
root,
}
},
}
</script>
```
</details>
<details>
<summary>
❌ Render Function / JSX in <code>setup()</code>
</summary>
```jsx
export default {
setup() {
const root = ref(null)
return () =>
h('div', {
ref: root,
})
// with JSX
return () => <div ref={root} />
},
}
```
</details>
<details>
<summary>
⚠️ <code>$refs</code> accessing workaround
</summary>
<br>
> :warning: **Warning**: The `SetupContext.refs` won't exist in `Vue 3.0`. `@vue/composition-api` provide it as a workaround here.
If you really want to use template refs in this case, you can access `vm.$refs` via `SetupContext.refs`
```jsx
export default {
setup(initProps, setupContext) {
const refs = setupContext.refs
onMounted(() => {
// the DOM element will be assigned to the ref after initial render
console.log(refs.root) // <div/>
})
return () =>
h('div', {
ref: 'root',
})
// with JSX
return () => <div ref="root" />
},
}
```
</details>
### Reactive
<details>
<summary>
⚠️ <code>reactive()</code> <b>mutates</b> the original object
</summary>
`reactive` uses `Vue.observable` underneath which will ***mutate*** the original object.
> :bulb: In Vue 3, it will return a new proxy object.
</details>
<details>
<summary>
⚠️ <code>set</code> and <code>del</code> workaround for adding and deleting reactive properties
</summary>
> ⚠️ Warning: `set` and `del` do NOT exist in Vue 3. We provide them as a workaround here, due to the limitation of [Vue 2.x reactivity system](https://vuejs.org/v2/guide/reactivity.html#For-Objects).
>
> In Vue 2, you will need to call `set` to track new keys on an `object`(similar to `Vue.set` but for `reactive objects` created by the Composition API). In Vue 3, you can just assign them like normal objects.
>
> Similarly, in Vue 2 you will need to call `del` to [ensure a key deletion triggers view updates](https://vuejs.org/v2/api/#Vue-delete) in reactive objects (similar to `Vue.delete` but for `reactive objects` created by the Composition API). In Vue 3 you can just delete them by calling `delete foo.bar`.
```ts
import { reactive, set, del } from '@vue/composition-api'
const a = reactive({
foo: 1
})
// add new reactive key
set(a, 'bar', 1)
// remove a key and trigger reactivity
del(a, 'bar')
```
</details>
### Watch
<details>
<summary>
❌ <code>onTrack</code> and <code>onTrigger</code> are not available in <code>WatchOptions</code>
</summary>
```js
watch(() => {
/* ... */
}, {
immediate: true,
onTrack() {}, // not available
onTrigger() {}, // not available
})
```
</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 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.component('Bar', Bar)
```
</details>
### `createElement` / `h`
<details>
<summary>
⚠️ <code>createElement</code> / <code>h</code> workaround
</summary>
<br>
`createElement` / `h` in Vue 2 is only accessable in `render()` function. To use it outside of `render()`, you can explicitly bind a component instance to it.
> :warning: **Warning**: This ability is provided as a workaround Vue 2, it's not part of the Vue 3 API.
```jsx
import { h as _h } from '@vue/composition-api'
export default {
setup() {
const vm = getCurrentInstance()
const h = _h.bind(vm)
return () =>
h('div', {
ref: 'root',
})
},
}
```
</details>
### `shallowReadonly`
<details>
<summary>
⚠️ <code>shallowReadonly()</code> will create a new object and with the same root properties, new properties added will <b>not</b> be readonly or reactive.
</summary>
> :bulb: In Vue 3, it will return a new proxy object.
</details>
### `readonly`
<details>
<summary>
⚠️ <code>readonly()</code> provides <b>only type-level</b> readonly check.
</summary>
`readonly()` is provided as API alignment with Vue 3 on type-level only. Use <code>isReadonly()</code> on it or it's properties can not be guaranteed.
</details>
### `props`
<details>
<summary>
⚠️ <code>toRefs(props.foo)</code> will incorrectly warn when accessing nested levels of props. <br>
&nbsp;&nbsp;&nbsp;&nbsp;⚠️ <code>isReactive(props.foo)</code> will return false.
</summary>
```ts
defineComponent({
setup(props) {
const { bar } = toRefs(props.foo) // it will `warn`
// use this instead
const { foo } = toRefs(props)
const a = foo.value.bar
}
})
```
</details>
### `computed().effect`
<details>
<summary>
⚠️ <code>computed()</code> has a property <code>effect</code> set to <code>true</code> instead of a <code>ReactiveEffect<T></code>.
</summary>
Due to the difference in implementation, there is no such concept as a `ReactiveEffect` in `@vue/composition-api`. Therefore, `effect` is merely `true` to enable differentiating computed from refs:
```ts
function isComputed<T>(o: ComputedRef<T> | unknown): o is ComputedRef<T>
function isComputed(o: any): o is ComputedRef {
return !!(isRef(o) && o.effect)
}
```
</details>
### Missing APIs
The following APIs introduced in Vue 3 are not available in this plugin.
- `onRenderTracked`
- `onRenderTriggered`
- `isProxy`
### Reactive APIs in `data()`
<details>
<summary>
❌ Passing <code>ref</code>, <code>reactive</code> or other reactive apis to <code>data()</code> would not work.
</summary>
```jsx
export default {
data() {
return {
// will result { a: { value: 1 } } in template
a: ref(1),
}
},
}
```
</details>
### `emits` Options
<details>
<summary>
❌ <code>emits</code> option is provided in type-level only, in order to align with Vue 3's type interface. Does NOT have actual effects on the code.
</summary>
```ts
defineComponent({
emits: {
// has no effects
submit: (eventOption) => {
if (...) {
return true
} else {
console.warn('Invalid submit event payload!')
return false
}
}
}
})
```
</details>
### Performance Impact
Due the limitation of Vue2's public API. `@vue/composition-api` inevitably introduces some performance overhead. Note that in most scenarios, this shouldn't be the source of performance issues.
You can check the [benchmark results](https://antfu.github.io/vue-composition-api-benchmark-results/) for more details.
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