Application API | Vue.js

Application API
​
createApp()
​

Creates an application instance.

Type

ts
function createApp(rootComponent: Component, rootProps?: object): App

Details

The first argument is the root component. The second optional argument is the props to be passed to the root component.

Example

With inline root component:

js
import { createApp } from 'vue'

const app = createApp({
  /* root component options */
})

With imported component:

js
import { createApp } from 'vue'
import App from './App.vue'

const app = createApp(App)

See also Guide - Creating a Vue Application

createSSRApp()
​

Creates an application instance in SSR Hydration mode. Usage is exactly the same as createApp().

app.mount()
​

Mounts the application instance in a container element.

Type

ts
interface App {
  mount(rootContainer: Element | string): ComponentPublicInstance
}

Details

The argument can either be an actual DOM element or a CSS selector (the first matched element will be used). Returns the root component instance.

If the component has a template or a render function defined, it will replace any existing DOM nodes inside the container. Otherwise, if the runtime compiler is available, the innerHTML of the container will be used as the template.

In SSR hydration mode, it will hydrate the existing DOM nodes inside the container. If there are mismatches, the existing DOM nodes will be morphed to match the expected output.

For each app instance, mount() can only be called once.

Example

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

app.mount('#app')

Can also mount to an actual DOM element:

js
app.mount(document.body.firstChild)
app.unmount()
​

Unmounts a mounted application instance, triggering the unmount lifecycle hooks for all components in the application's component tree.

Type

ts
interface App {
  unmount(): void
}
app.component()
​

Registers a global component if passing both a name string and a component definition, or retrieves an already registered one if only the name is passed.

Type

ts
interface App {
  component(name: string): Component | undefined
  component(name: string, component: Component): this
}

Example

js
import { createApp } from 'vue'

const app = createApp({})

// register an options object
app.component('my-component', {
  /* ... */
})

// retrieve a registered component
const MyComponent = app.component('my-component')

See also Component Registration

app.directive()
​

Registers a global custom directive if passing both a name string and a directive definition, or retrieves an already registered one if only the name is passed.

Type

ts
interface App {
  directive(name: string): Directive | undefined
  directive(name: string, directive: Directive): this
}

Example

js
import { createApp } from 'vue'

const app = createApp({
  /* ... */
})

// register (object directive)
app.directive('my-directive', {
  /* custom directive hooks */
})

// register (function directive shorthand)
app.directive('my-directive', () => {
  /* ... */
})

// retrieve a registered directive
const myDirective = app.directive('my-directive')

See also Custom Directives

app.use()
​

Installs a plugin.

Type

ts
interface App {
  use(plugin: Plugin, ...options: any[]): this
}

Details

Expects the plugin as the first argument, and optional plugin options as the second argument.

The plugin can either be an object with an install() method, or just a function that will be used as the install() method. The options (second argument of app.use()) will be passed along to the plugin's install() method.

When app.use() is called on the same plugin multiple times, the plugin will be installed only once.

Example

js
import { createApp } from 'vue'
import MyPlugin from './plugins/MyPlugin'

const app = createApp({
  /* ... */
})

app.use(MyPlugin)

See also Plugins

app.mixin()
​

Applies a global mixin (scoped to the application). A global mixin applies its included options to every component instance in the application.

Not Recommended

Mixins are supported in Vue 3 mainly for backwards compatibility, due to their widespread use in ecosystem libraries. Use of mixins, especially global mixins, should be avoided in application code.

For logic reuse, prefer Composables instead.

Type

ts
interface App {
  mixin(mixin: ComponentOptions): this
}
app.provide()
​

Provide a value that can be injected in all descendant components within the application.

Type

ts
interface App {
  provide<T>(key: InjectionKey<T> | symbol | string, value: T): this
}

Details

Expects the injection key as the first argument, and the provided value as the second. Returns the application instance itself.

Example

js
import { createApp } from 'vue'

const app = createApp(/* ... */)

app.provide('message', 'hello')

Inside a component in the application:

js
import { inject } from 'vue'

export default {
  setup() {
    console.log(inject('message')) // 'hello'
  }
}

See also

Provide / Inject
App-level Provide
app.runWithContext()
app.runWithContext()
​

Execute a callback with the current app as injection context.

Type

ts
interface App {
  runWithContext<T>(fn: () => T): T
}

Details

Expects a callback function and runs the callback immediately. During the synchronous call of the callback, inject() calls are able to look up injections from the values provided by the current app, even when there is no current active component instance. The return value of the callback will also be returned.

Example

js
import { inject } from 'vue'

app.provide('id', 1)

const injected = app.runWithContext(() => {
  return inject('id')
})

console.log(injected) // 1
app.version
​

Provides the version of Vue that the application was created with. This is useful inside plugins, where you might need conditional logic based on different Vue versions.

Type

ts
interface App {
  version: string
}

Example

Performing a version check inside a plugin:

js
export default {
  install(app) {
    const version = Number(app.version.split('.')[0])
    if (version < 3) {
      console.warn('This plugin requires Vue 3')
    }
  }
}

See also Global API - version

app.config
​

Every application instance exposes a config object that contains the configuration settings for that application. You can modify its properties (documented below) before mounting your application.

js
import { createApp } from 'vue'

const app = createApp(/* ... */)

console.log(app.config)
app.config.errorHandler
​

Assign a global handler for uncaught errors propagating from within the application.

Type

ts
interface AppConfig {
  errorHandler?: (
    err: unknown,
    instance: ComponentPublicInstance | null,
    // `info` is a Vue-specific error info,
    // e.g. which lifecycle hook the error was thrown in
    info: string
  ) => void
}

Details

The error handler receives three arguments: the error, the component instance that triggered the error, and an information string specifying the error source type.

It can capture errors from the following sources:

Component renders
Event handlers
Lifecycle hooks
setup() function
Watchers
Custom directive hooks
Transition hooks

Example

js
app.config.errorHandler = (err, instance, info) => {
  // handle error, e.g. report to a service
}
app.config.warnHandler
​

Assign a custom handler for runtime warnings from Vue.

Type

ts
interface AppConfig {
  warnHandler?: (
    msg: string,
    instance: ComponentPublicInstance | null,
    trace: string
  ) => void
}

Details

The warning handler receives the warning message as the first argument, the source component instance as the second argument, and a component trace string as the third.

It can be used to filter out specific warnings to reduce console verbosity. All Vue warnings should be addressed during development, so this is only recommended during debug sessions to focus on specific warnings among many, and should be removed once the debugging is done.

TIP

Warnings only work during development, so this config is ignored in production mode.

Example

js
app.config.warnHandler = (msg, instance, trace) => {
  // `trace` is the component hierarchy trace
}
app.config.performance
​

Set this to true to enable component init, compile, render and patch performance tracing in the browser devtool performance/timeline panel. Only works in development mode and in browsers that support the performance.mark API.

Type: boolean

See also Guide - Performance

app.config.compilerOptions
​

Configure runtime compiler options. Values set on this object will be passed to the in-browser template compiler and affect every component in the configured app. Note you can also override these options on a per-component basis using the compilerOptions option.

Important

This config option is only respected when using the full build (i.e. the standalone vue.js that can compile templates in the browser). If you are using the runtime-only build with a build setup, compiler options must be passed to @vue/compiler-dom via build tool configurations instead.

For vue-loader: pass via the compilerOptions loader option. Also see how to configure it in vue-cli.

For vite: pass via @vitejs/plugin-vue options.

app.config.compilerOptions.isCustomElement
​

Specifies a check method to recognize native custom elements.

Type: (tag: string) => boolean

Details

Should return true if the tag should be treated as a native custom element. For a matched tag, Vue will render it as a native element instead of attempting to resolve it as a Vue component.

Native HTML and SVG tags don't need to be matched in this function - Vue's parser recognizes them automatically.

Example

js
// treat all tags starting with 'ion-' as custom elements
app.config.compilerOptions.isCustomElement = (tag) => {
  return tag.startsWith('ion-')
}

See also Vue and Web Components

app.config.compilerOptions.whitespace
​

Adjusts template whitespace handling behavior.

Type: 'condense' | 'preserve'

Default: 'condense'

Details

Vue removes / condenses whitespace characters in templates to produce more efficient compiled output. The default strategy is "condense", with the following behavior:

Leading / ending whitespace characters inside an element are condensed into a single space.
Whitespace characters between elements that contain newlines are removed.
Consecutive whitespace characters in text nodes are condensed into a single space.

Setting this option to 'preserve' will disable (2) and (3).

Example

js
app.config.compilerOptions.whitespace = 'preserve'
app.config.compilerOptions.delimiters
​

Adjusts the delimiters used for text interpolation within the template.

Type: [string, string]

Default: ['{{', '}}']

Details

This is typically used to avoid conflicting with server-side frameworks that also use mustache syntax.

Example

js
// Delimiters changed to ES6 template string style
app.config.compilerOptions.delimiters = ['${', '}']
app.config.compilerOptions.comments
​

Adjusts treatment of HTML comments in templates.

Type: boolean

Default: false

Details

By default, Vue will remove the comments in production. Setting this option to true will force Vue to preserve comments even in production. Comments are always preserved during development. This option is typically used when Vue is used with other libraries that rely on HTML comments.

Example

js
app.config.compilerOptions.comments = true
app.config.globalProperties
​

An object that can be used to register global properties that can be accessed on any component instance inside the application.

Type

ts
interface AppConfig {
  globalProperties: Record<string, any>
}

Details

This is a replacement of Vue 2's Vue.prototype which is no longer present in Vue 3. As with anything global, this should be used sparingly.

If a global property conflicts with a component’s own property, the component's own property will have higher priority.

Usage

js
app.config.globalProperties.msg = 'hello'

This makes msg available inside any component template in the application, and also on this of any component instance:

js
export default {
  mounted() {
    console.log(this.msg) // 'hello'
  }
}

See also Guide - Augmenting Global Properties 

app.config.optionMergeStrategies
​

An object for defining merging strategies for custom component options.

Type

ts
interface AppConfig {
  optionMergeStrategies: Record<string, OptionMergeFunction>
}

type OptionMergeFunction = (to: unknown, from: unknown) => any

Details

Some plugins / libraries add support for custom component options (by injecting global mixins). These options may require special merging logic when the same option needs to be "merged" from multiple sources (e.g. mixins or component inheritance).

A merge strategy function can be registered for a custom option by assigning it on the app.config.optionMergeStrategies object using the option's name as the key.

The merge strategy function receives the value of that option defined on the parent and child instances as the first and second arguments, respectively.

Example

js
const app = createApp({
  // option from self
  msg: 'Vue',
  // option from a mixin
  mixins: [
    {
      msg: 'Hello '
    }
  ],
  mounted() {
    // merged options exposed on this.$options
    console.log(this.$options.msg)
  }
})

// define a custom merge strategy for `msg`
app.config.optionMergeStrategies.msg = (parent, child) => {
  return (parent || '') + (child || '')
}

app.mount('#app')
// logs 'Hello Vue'

See also Component Instance - $options