@vue/composition-api

Vue 2 plugin for Composition API

English | 中文 ・ Composition API Docs

⚠️ With the release of Vue 2.7, 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

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 to compose your component.

import Vue from 'vue'
import VueCompositionAPI from '@vue/composition-api'

Vue.use(VueCompositionAPI)

// use the APIs
import { ref, reactive } from '@vue/composition-api'

💡 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.

<script src="https://cdn.jsdelivr.net/npm/[email protected]"></script>
<script src="https://cdn.jsdelivr.net/npm/@vue/[email protected]"></script>

@vue/composition-api will be exposed to global variable window.VueCompositionAPI.

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

import { defineComponent } from '@vue/composition-api'

export default defineComponent({
  // type inference enabled
})

JSX/TSX

JSX is now officially supported on vuejs/jsx. You can enable it by following this document. A community maintained version can be found at babel-preset-vca-jsx by @luwanquan.

To support TSX, create a declaration file with the following content in your project.

// 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.

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

✅ Support     ❌ Not Supported

Ref Unwrap

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

const b = reactive({
  list: [
    {
      count: ref(0), // no unwrap!!
    },
  ],
})

// no unwrap for `count`, `.value` is required
b.list[0].count.value === 0 // true

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

Template Refs

<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>

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" />
  },
}

<template>
  <div :ref="el => root = el"></div>
</template>

<script>
  export default {
    setup() {
      const root = ref(null)

      return {
        root,
      }
    },
  }
</script>

export default {
  setup() {
    const root = ref(null)

    return () =>
      h('div', {
        ref: root,
      })

    // with JSX
    return () => <div ref={root} />
  },
}

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" />
  },
}

Reactive

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')

Watch

watch(() => {
    /* ... */
}, {
  immediate: true,
  onTrack() {}, // not available
  onTrigger() {}, // not available
})

createApp

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)

createElement / h

import { h as _h } from '@vue/composition-api'

export default {
  setup() {
    const vm = getCurrentInstance()
    const h = _h.bind(vm)

    return () =>
      h('div', {
        ref: 'root',
      })
  },
}

shallowReadonly

readonly

props

defineComponent({
  setup(props) {
    const { bar } = toRefs(props.foo) // it will `warn`

    // use this instead
    const { foo } = toRefs(props)
    const a = foo.value.bar
  }
})

computed().effect

function isComputed<T>(o: ComputedRef<T> | unknown): o is ComputedRef<T>
function isComputed(o: any): o is ComputedRef {
  return !!(isRef(o) && o.effect)
}

Missing APIs

The following APIs introduced in Vue 3 are not available in this plugin.

• onRenderTracked
• onRenderTriggered
• isProxy

Reactive APIs in data()

export default {
  data() {
    return {
      // will result { a: { value: 1 } } in template
      a: ref(1),
    }
  },
}

emits Options

defineComponent({
  emits: {
    // has no effects
    submit: (eventOption) => {
      if (...) {
        return true
      } else {
        console.warn('Invalid submit event payload!')
        return false
      }
    }
  }
})

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 for more details.