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149 lines
6.6 KiB
Markdown
149 lines
6.6 KiB
Markdown
---
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title: 'useAsyncData'
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description: useAsyncData provides access to data that resolves asynchronously in an SSR-friendly composable.
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links:
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- label: Source
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icon: i-simple-icons-github
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to: https://github.com/nuxt/nuxt/blob/main/packages/nuxt/src/app/composables/asyncData.ts
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size: xs
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---
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Within your pages, components, and plugins you can use useAsyncData to get access to data that resolves asynchronously.
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::note
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[`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.
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::
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## Usage
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```vue [pages/index.vue]
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<script setup lang="ts">
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const { data, status, error, refresh, clear } = await useAsyncData(
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'mountains',
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() => $fetch('https://api.nuxtjs.dev/mountains')
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)
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</script>
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```
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::warning
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If you're using a custom useAsyncData wrapper, do not await it in the composable, as that can cause unexpected behavior. Please follow [this recipe](/docs/guide/recipes/custom-usefetch#custom-usefetch) for more information on how to make a custom async data fetcher.
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::
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::note
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`data`, `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.
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::
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### Watch Params
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The built-in `watch` option allows automatically rerunning the fetcher function when any changes are detected.
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```vue [pages/index.vue]
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<script setup lang="ts">
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const page = ref(1)
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const { data: posts } = await useAsyncData(
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'posts',
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() => $fetch('https://fakeApi.com/posts', {
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params: {
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page: page.value
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}
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}), {
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watch: [page]
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}
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)
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</script>
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```
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::warning
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[`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) .
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::
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:read-more{to="/docs/getting-started/data-fetching#useasyncdata"}
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## Params
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- `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.
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- `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
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- `options`:
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- `server`: whether to fetch the data on the server (defaults to `true`)
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- `lazy`: whether to resolve the async function after loading the route, instead of blocking client-side navigation (defaults to `false`)
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- `immediate`: when set to `false`, will prevent the request from firing immediately. (defaults to `true`)
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- `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
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- `transform`: a function that can be used to alter `handler` function result after resolving
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- `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.
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- `pick`: only pick specified keys in this array from the `handler` function result
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- `watch`: watch reactive sources to auto-refresh
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- `deep`: return data in a deep ref object. It is `false` by default to return data in a shallow ref object for performance.
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- `dedupe`: avoid fetching same key more than once at a time (defaults to `cancel`). Possible options:
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- `cancel` - cancels existing requests when a new one is made
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- `defer` - does not make new requests at all if there is a pending request
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::note
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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.
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::
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::read-more{to="/docs/api/composables/use-lazy-async-data"}
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You can use `useLazyAsyncData` to have the same behavior as `lazy: true` with `useAsyncData`.
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::
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::tip{icon="i-simple-icons-youtube" color="gray" to="https://www.youtube.com/watch?v=aQPR0xn-MMk" target="_blank"}
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Learn how to use `transform` and `getCachedData` to avoid superfluous calls to an API and cache data for visitors on the client.
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::
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## Return Values
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- `data`: the result of the asynchronous function that is passed in.
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- `refresh`/`execute`: a function that can be used to refresh the data returned by the `handler` function.
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- `error`: an error object if the data fetching failed.
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- `status`: a string indicating the status of the data request (`"idle"`, `"pending"`, `"success"`, `"error"`).
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- `clear`: a function which will set `data` to `undefined`, set `error` to `null`, set `status` to `'idle'`, and mark any currently pending requests as cancelled.
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By default, Nuxt waits until a `refresh` is finished before it can be executed again.
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::note
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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>`.
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::
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## Type
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```ts [Signature]
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function useAsyncData<DataT, DataE>(
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handler: (nuxtApp?: NuxtApp) => Promise<DataT>,
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options?: AsyncDataOptions<DataT>
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): AsyncData<DataT, DataE>
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function useAsyncData<DataT, DataE>(
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key: string,
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handler: (nuxtApp?: NuxtApp) => Promise<DataT>,
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options?: AsyncDataOptions<DataT>
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): Promise<AsyncData<DataT, DataE>>
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type AsyncDataOptions<DataT> = {
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server?: boolean
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lazy?: boolean
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immediate?: boolean
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deep?: boolean
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dedupe?: 'cancel' | 'defer'
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default?: () => DataT | Ref<DataT> | null
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transform?: (input: DataT) => DataT | Promise<DataT>
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pick?: string[]
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watch?: WatchSource[]
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getCachedData?: (key: string, nuxtApp: NuxtApp) => DataT
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}
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type AsyncData<DataT, ErrorT> = {
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data: Ref<DataT | null>
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refresh: (opts?: AsyncDataExecuteOptions) => Promise<void>
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execute: (opts?: AsyncDataExecuteOptions) => Promise<void>
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clear: () => void
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error: Ref<ErrorT | null>
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status: Ref<AsyncDataRequestStatus>
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};
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interface AsyncDataExecuteOptions {
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dedupe?: 'cancel' | 'defer'
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}
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type AsyncDataRequestStatus = 'idle' | 'pending' | 'success' | 'error'
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```
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:read-more{to="/docs/getting-started/data-fetching"}
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