# Dynamic & Async Components

This page assumes you've already read the Components Basics. Read that first if you are new to components.

# Dynamic Components with keep-alive

Earlier, we used the is attribute to switch between components in a tabbed interface:

<component :is="currentTabComponent"></component>
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When switching between these components though, you'll sometimes want to maintain their state or avoid re-rendering for performance reasons. For example, when expanding our tabbed interface a little:

See the Pen Dynamic components: without keep-alive by Vue (@Vue) on CodePen.

You'll notice that if you select a post, switch to the Archive tab, then switch back to Posts, it's no longer showing the post you selected. That's because each time you switch to a new tab, Vue creates a new instance of the currentTabComponent.

Recreating dynamic components is normally useful behavior, but in this case, we'd really like those tab component instances to be cached once they're created for the first time. To solve this problem, we can wrap our dynamic component with a <keep-alive> element:

<!-- Inactive components will be cached! -->
<keep-alive>
  <component :is="currentTabComponent"></component>
</keep-alive>
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Check out the result below:

See the Pen Dynamic components: with keep-alive by Vue (@Vue) on CodePen.

Now the Posts tab maintains its state (the selected post) even when it's not rendered.

Check out more details on <keep-alive> in the API reference.

# Async Components

In large applications, we may need to divide the app into smaller chunks and only load a component from the server when it's needed. To make that possible, Vue has a defineAsyncComponent method:

const app = Vue.createApp({})

const AsyncComp = Vue.defineAsyncComponent(
  () =>
    new Promise((resolve, reject) => {
      resolve({
        template: '<div>I am async!</div>'
      })
    })
)

app.component('async-example', AsyncComp)
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As you can see, this method accepts a factory function returning a Promise. Promise's resolve callback should be called when you have retrieved your component definition from the server. You can also call reject(reason) to indicate the load has failed.

You can also return a Promise in the factory function, so with Webpack 2 or later and ES2015 syntax you can do:

import { defineAsyncComponent } from 'vue'

const AsyncComp = defineAsyncComponent(() =>
  import('./components/AsyncComponent.vue')
)

app.component('async-component', AsyncComp)
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You can also use defineAsyncComponent when registering a component locally:

import { createApp, defineAsyncComponent } from 'vue'

createApp({
  // ...
  components: {
    AsyncComponent: defineAsyncComponent(() =>
      import('./components/AsyncComponent.vue')
    )
  }
})
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# Using with Suspense

Async components are suspensible by default. This means if it has a <Suspense> in the parent chain, it will be treated as an async dependency of that <Suspense>. In this case, the loading state will be controlled by the <Suspense>, and the component's own loading, error, delay and timeout options will be ignored.

The async component can opt-out of Suspense control and let the component always control its own loading state by specifying suspensible: false in its options.

You can check the list of available options in the API Reference

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Last updated: 7/15/2020, 10:33:55 AM