Nuxt/docs/3.api/2.composables/use-async-data.md

---
title: 'useAsyncData'
description: useAsyncData provides access to data that resolves asynchronously in a SSR-friendly composable.
links:
  - label: Source
    icon: i-simple-icons-github
    to: https://github.com/nuxt/nuxt/blob/main/packages/nuxt/src/app/composables/asyncData.ts
    size: xs
---

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

::callout
[`useAsyncData`](/docs/api/composables/use-async-data) is a composable meant to be called directly in a setup function, plugin, or route middleware. 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.
::

## Usage

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

### Watch Params

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

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

::callout{color="amber" icon="i-ph-warning-duotone"}
[`useAsyncData`](/docs/api/composables/use-async-data) is a reserved function name transformed by the compiler, so you should not name your own function [`useAsyncData`](/docs/api/composables/use-async-data) .
::

:read-more{to="/docs/getting-started/data-fetching#useasyncdata"}

## 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
- `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. A _null_ or _undefined_ return value will trigger a fetch. By default, this is: `key => nuxt.isHydrating ? nuxt.payload.data[key] : nuxt.static.data[key]`, which only caches data when `payloadExtraction` 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 `true` by default). It can be set to `false` 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

::callout
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.
::

::read-more{to="/docs/api/composables/use-lazy-async-data"}
You can use `useLazyAsyncData` to have the same behavior as `lazy: true` with `useAsyncData`.
::

::callout{icon="i-simple-icons-youtube" color="gray" to="https://www.youtube.com/watch?v=aQPR0xn-MMk" target="_blank"}
Learn how to use `transform` and `getCachedData` to avoid superfluous calls to an API and cache data for visitors on the client.
::

## Return Values

- `data`: the result of the asynchronous function that is passed in.
- `pending`: a boolean indicating whether the data is still being fetched.
- `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"`, `"pending"`, `"success"`, `"error"`).

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

::callout
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/api/composables/use-async-data) on the client side, `data` will remain `null` within `<script setup>`.
::

## Type

```ts [Signature]
function useAsyncData<DataT, DataE>(
  handler: (nuxtApp?: NuxtApp) => Promise<DataT>,
  options?: AsyncDataOptions<DataT>
): AsyncData<DataT, DataE>
function useAsyncData<DataT, DataE>(
  key: string,
  handler: (nuxtApp?: NuxtApp) => Promise<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
  pick?: string[]
  watch?: WatchSource[]
  getCachedData?: (key: string) => DataT
}

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

interface AsyncDataExecuteOptions {
  dedupe?: 'cancel' | 'defer'
}

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

:read-more{to="/docs/getting-started/data-fetching"}