# Source: https://nuxt.com/raw/docs/3.x/api/composables/use-async-data.md

# Source: https://nuxt.com/raw/docs/4.x/api/composables/use-async-data.md

# useAsyncData

> useAsyncData provides access to data that resolves asynchronously in an SSR-friendly composable.

Within your pages, components, and plugins you can use useAsyncData to get access to data that resolves asynchronously.

<note>

[`useAsyncData`](/docs/4.x/api/composables/use-async-data) is a composable meant to be called directly in the [Nuxt context](/docs/4.x/guide/going-further/nuxt-app#the-nuxt-context). It returns reactive composables and handles adding responses to the Nuxt payload so they can be passed from server to client **without re-fetching the data on client side** when the page hydrates.

</note>

## Usage

```vue [app/pages/index.vue]
<script setup lang="ts">
const { data, status, pending, error, refresh, clear } = await useAsyncData(
  'mountains',
  (_nuxtApp, { signal }) => $fetch('https://api.nuxtjs.dev/mountains', { signal }),
)
</script>
```

<warning to="/docs/4.x/guide/recipes/custom-usefetch#custom-usefetchuseasyncdata">

If you're using a custom `useAsyncData` wrapper, do not await it in the composable as that can cause unexpected behavior. See recipe for custom async data fetcher.

</warning>

<note>

`data`, `status`, `pending` and `error` are Vue refs and they should be accessed with `.value` when used within the `<script setup>`, while `refresh`/`execute` and `clear` are plain functions.

</note>

### Watch Params

The built-in `watch` option allows automatically rerunning the fetcher function when any changes are detected.

```vue [app/pages/index.vue]
<script setup lang="ts">
const page = ref(1)
const { data: posts } = await useAsyncData(
  'posts',
  (_nuxtApp, { signal }) => $fetch('https://fakeApi.com/posts', {
    params: {
      page: page.value,
    },
    signal,
  }), {
    watch: [page],
  },
)
</script>
```

### Reactive Keys

You can use a computed ref, plain ref or a getter function as the key, allowing for dynamic data fetching that automatically updates when the key changes:

```vue [app/pages/[id].vue]
<script setup lang="ts">
const route = useRoute()
const userId = computed(() => `user-${route.params.id}`)

// When the route changes and userId updates, the data will be automatically refetched
const { data: user } = useAsyncData(
  userId,
  () => fetchUserById(route.params.id),
)
</script>
```

### Make your `handler` abortable

You can make your `handler` function abortable by using the `signal` provided in the second argument. This is useful for cancelling requests when they are no longer needed, such as when a user navigates away from a page. `$fetch` natively supports abort signals.

```ts
const { data, error } = await useAsyncData(
  'users',
  (_nuxtApp, { signal }) => $fetch('/api/users', { signal }),
)

refresh() // will actually cancel the $fetch request (if dedupe: cancel)
refresh() // will actually cancel the $fetch request (if dedupe: cancel)
refresh()

clear() // will cancel the latest pending handler
```

You can also pass an `AbortSignal` to the `refresh`/`execute` function to cancel individual requests manually.

```ts
const { refresh } = await useAsyncData(
  'users',
  (_nuxtApp, { signal }) => $fetch('/api/users', { signal }),
)
let abortController: AbortController | undefined

function handleUserAction () {
  abortController = new AbortController()
  refresh({ signal: abortController.signal })
}

function handleCancel () {
  abortController?.abort() // aborts the ongoing refresh request
}
```

If your `handler` function does not support abort signals, you can implement your own abort logic using the `signal` provided.

```ts
const { data, error } = await useAsyncData(
  'users',
  (_nuxtApp, { signal }) => {
    return new Promise((resolve, reject) => {
      signal?.addEventListener('abort', () => {
        reject(new Error('Request aborted'))
      })
      return Promise.resolve(callback.call(this, yourHandler)).then(resolve, reject)
    })
  },
)
```

The handler signal will be aborted when:

- A new request is made with `dedupe: 'cancel'`
- The `clear` function is called
- The `options.timeout` duration is exceeded

<warning>

[`useAsyncData`](/docs/4.x/api/composables/use-async-data) is a reserved function name transformed by the compiler, so you should not name your own function [`useAsyncData`](/docs/4.x/api/composables/use-async-data).

</warning>

<read-more to="/docs/4.x/getting-started/data-fetching#useasyncdata">



</read-more>

## Params

- `key`: a unique key to ensure that data fetching can be properly de-duplicated across requests. If you do not provide a key, then a key that is unique to the file name and line number of the instance of `useAsyncData` will be generated for you.
- `handler`: an asynchronous function that must return a truthy value (for example, it should not be `undefined` or `null`) or the request may be duplicated on the client side.
<warning>

The `handler` function should be **side-effect free** to ensure predictable behavior during SSR and CSR hydration. If you need to trigger side effects, use the [`callOnce`](/docs/4.x/api/utils/call-once) utility to do so.

</warning>
- `options`:

  - `server`: whether to fetch the data on the server (defaults to `true`)
  - `lazy`: whether to resolve the async function after loading the route, instead of blocking client-side navigation (defaults to `false`)
  - `immediate`: when set to `false`, will prevent the request from firing immediately. (defaults to `true`)
  - `default`: a factory function to set the default value of the `data`, before the async function resolves - useful with the `lazy: true` or `immediate: false` option
  - `transform`: a function that can be used to alter `handler` function result after resolving
  - `getCachedData`: Provide a function which returns cached data. An `undefined` return value will trigger a fetch. By default, this is:
  ```ts
  const getDefaultCachedData = (key, nuxtApp, ctx) => nuxtApp.isHydrating
    ? nuxtApp.payload.data[key]
    : nuxtApp.static.data[key]
  ```
  
  
  Which only caches data when `experimental.payloadExtraction` of `nuxt.config` is enabled.
  - `pick`: only pick specified keys in this array from the `handler` function result
  - `watch`: watch reactive sources to auto-refresh
  - `deep`: return data in a deep ref object. It is `false` by default to return data in a shallow ref object, which can improve performance if your data does not need to be deeply reactive.
  - `dedupe`: avoid fetching same key more than once at a time (defaults to `cancel`). Possible options:
  
    - `cancel` - cancels existing requests when a new one is made
    - `defer` - does not make new requests at all if there is a pending request
  - `timeout` - a number in milliseconds to wait before timing out the request (defaults to `undefined`, which means no timeout)

<note>

Under the hood, `lazy: false` uses `<Suspense>` to block the loading of the route before the data has been fetched. Consider using `lazy: true` and implementing a loading state instead for a snappier user experience.

</note>

<read-more to="/docs/4.x/api/composables/use-lazy-async-data">

You can use `useLazyAsyncData` to have the same behavior as `lazy: true` with `useAsyncData`.

</read-more>

<video-accordion title="Watch a video from Alexander Lichter about client-side caching with getCachedData" video-id="aQPR0xn-MMk">



</video-accordion>

### Shared State and Option Consistency

When using the same key for multiple `useAsyncData` calls, they will share the same `data`, `error`, `status` and `pending` refs. This ensures consistency across components but requires option consistency.

The following options **must be consistent** across all calls with the same key:

- `handler` function
- `deep` option
- `transform` function
- `pick` array
- `getCachedData` function
- `default` value

The following options **can differ** without triggering warnings:

- `server`
- `lazy`
- `immediate`
- `dedupe`
- `watch`

```ts
// ❌ This will trigger a development warning
const { data: users1 } = useAsyncData('users', (_nuxtApp, { signal }) => $fetch('/api/users', { signal }), { deep: false })
const { data: users2 } = useAsyncData('users', (_nuxtApp, { signal }) => $fetch('/api/users', { signal }), { deep: true })

// ✅ This is allowed
const { data: users1 } = useAsyncData('users', (_nuxtApp, { signal }) => $fetch('/api/users', { signal }), { immediate: true })
const { data: users2 } = useAsyncData('users', (_nuxtApp, { signal }) => $fetch('/api/users', { signal }), { immediate: false })
```

<tip>

Keyed state created using `useAsyncData` can be retrieved across your Nuxt application using [`useNuxtData`](/docs/4.x/api/composables/use-nuxt-data).

</tip>

## Return Values

- `data`: the result of the asynchronous function that is passed in.
- `refresh`/`execute`: a function that can be used to refresh the data returned by the `handler` function.
- `error`: an error object if the data fetching failed.
- `status`: a string indicating the status of the data request:

  - `idle`: when the request has not started, such as:
  
    - when `execute` has not yet been called and `{ immediate: false }` is set
    - when rendering HTML on the server and `{ server: false }` is set
  - `pending`: the request is in progress
  - `success`: the request has completed successfully
  - `error`: the request has failed
- `pending`: a `Ref<boolean>` that is `true` while the request is in progress (that is, while `status.value === 'pending'`).
- `clear`: a function that can be used to set `data` to `undefined` (or the value of `options.default()` if provided), set `error` to `undefined`, set `status` to `idle`, and mark any currently pending requests as cancelled.

By default, Nuxt waits until a `refresh` is finished before it can be executed again.

<note>

If you have not fetched data on the server (for example, with `server: false`), then the data *will not* be fetched until hydration completes. This means even if you await [`useAsyncData`](/docs/4.x/api/composables/use-async-data) on the client side, `data` will remain `undefined` within `<script setup>`.

</note>

## Type

```ts [Signature]
export type AsyncDataHandler<ResT> = (nuxtApp: NuxtApp, options: { signal: AbortSignal }) => Promise<ResT>

export function useAsyncData<DataT, DataE> (
  handler: AsyncDataHandler<DataT>,
  options?: AsyncDataOptions<DataT>,
): AsyncData<DataT, DataE>
export function useAsyncData<DataT, DataE> (
  key: MaybeRefOrGetter<string>,
  handler: AsyncDataHandler<DataT>,
  options?: AsyncDataOptions<DataT>,
): Promise<AsyncData<DataT, DataE>>

type AsyncDataOptions<DataT> = {
  server?: boolean
  lazy?: boolean
  immediate?: boolean
  deep?: boolean
  dedupe?: 'cancel' | 'defer'
  default?: () => DataT | Ref<DataT> | null
  transform?: (input: DataT) => DataT | Promise<DataT>
  pick?: string[]
  watch?: MultiWatchSources | false
  getCachedData?: (key: string, nuxtApp: NuxtApp, ctx: AsyncDataRequestContext) => DataT | undefined
  timeout?: number
}

type AsyncDataRequestContext = {
  /** The reason for this data request */
  cause: 'initial' | 'refresh:manual' | 'refresh:hook' | 'watch'
}

type AsyncData<DataT, ErrorT> = {
  data: Ref<DataT | undefined>
  refresh: (opts?: AsyncDataExecuteOptions) => Promise<void>
  execute: (opts?: AsyncDataExecuteOptions) => Promise<void>
  clear: () => void
  error: Ref<ErrorT | undefined>
  status: Ref<AsyncDataRequestStatus>
  pending: Ref<boolean>
}

interface AsyncDataExecuteOptions {
  dedupe?: 'cancel' | 'defer'
  timeout?: number
  signal?: AbortSignal
}

type AsyncDataRequestStatus = 'idle' | 'pending' | 'success' | 'error'
```

<read-more to="/docs/4.x/getting-started/data-fetching">



</read-more>