Async Components
新機能

Overview

Here is a high level overview of what has changed:

New defineAsyncComponent helper method that explicitly defines async components
component option renamed to loader
Loader function does not inherently receive resolve and reject arguments and must return a Promise

For a more in-depth explanation, read on!

Introduction

Previously, async components were created by simply defining a component as a function that returned a promise, such as:

const asyncModal = () => import('./Modal.vue')

Or, for the more advanced component syntax with options:

const asyncModal = {
  component: () => import('./Modal.vue'),
  delay: 200,
  timeout: 3000,
  error: ErrorComponent,
  loading: LoadingComponent
}

3.x Syntax

Now, in Vue 3, since functional components are defined as pure functions, async components definitions need to be explicitly defined by wrapping it in a new defineAsyncComponent helper:

import { defineAsyncComponent } from 'vue'
import ErrorComponent from './components/ErrorComponent.vue'
import LoadingComponent from './components/LoadingComponent.vue'

// Async component without options
const asyncModal = defineAsyncComponent(() => import('./Modal.vue'))

// Async component with options
const asyncModalWithOptions = defineAsyncComponent({
  loader: () => import('./Modal.vue'),
  delay: 200,
  timeout: 3000,
  errorComponent: ErrorComponent,
  loadingComponent: LoadingComponent
})

NOTE

Vue Router supports a similar mechanism for asynchronously loading route components, known as lazy loading. Despite the similarities, this feature is distinct from Vue's support for async components. You should not use defineAsyncComponent when configuring route components with Vue Router. You can read more about this in the Lazy Loading Routes section of the Vue Router documentation.

Another change that has been made from 2.x is that the component option is now renamed to loader in order to accurately communicate that a component definition cannot be provided directly.

import { defineAsyncComponent } from 'vue'

const asyncModalWithOptions = defineAsyncComponent({
  loader: () => import('./Modal.vue'),
  delay: 200,
  timeout: 3000,
  errorComponent: ErrorComponent,
  loadingComponent: LoadingComponent
})

In addition, unlike 2.x, the loader function no longer receives the resolve and reject arguments and must always return a Promise.

// 2.x version
const oldAsyncComponent = (resolve, reject) => {
  /* ... */
}

// 3.x version
const asyncComponent = defineAsyncComponent(
  () =>
    new Promise((resolve, reject) => {
      /* ... */
    })
)

For more information on the usage of async components, see:

Async Components 新機能 #

Overview #

Introduction #

3.x Syntax #

Async Components
新機能

Overview

Introduction

3.x Syntax