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

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---
title: 'useAsyncData'
description: useAsyncData provides access to data that resolves asynchronously in an 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.
::note
[`useAsyncData`](/docs/api/composables/use-async-data) is a composable meant to be called directly in the [Nuxt context](/docs/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.
::
## Usage
```vue [pages/index.vue]
<script setup lang="ts">
const { data, pending, error, refresh, clear } = await useAsyncData(
'mountains',
() => $fetch('https://api.nuxtjs.dev/mountains')
)
</script>
```
::note
`data`, `pending`, `status` 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.
::
### Watch Params
The built-in `watch` option allows automatically rerunning the fetcher function when any changes are detected.
```vue [pages/index.vue]
<script setup lang="ts">
const page = ref(1)
const { data: posts } = await useAsyncData(
'posts',
() => $fetch('https://fakeApi.com/posts', {
params: {
page: page.value
}
}), {
watch: [page]
}
)
</script>
```
::warning
[`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
::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.
::
::read-more{to="/docs/api/composables/use-lazy-async-data"}
You can use `useLazyAsyncData` to have the same behavior as `lazy: true` with `useAsyncData`.
::
::tip{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"`).
- `clear`: a function which will set `data` to `undefined`, set `error` to `null`, set `pending` to `false`, 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/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 | Promise<DataT>
pick?: string[]
watch?: WatchSource[]
getCachedData?: (key: string, nuxtApp: NuxtApp) => DataT
}
type AsyncData<DataT, ErrorT> = {
data: Ref<DataT | null>
pending: Ref<boolean>
refresh: (opts?: AsyncDataExecuteOptions) => Promise<void>
execute: (opts?: AsyncDataExecuteOptions) => Promise<void>
clear: () => 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"}