# `useAsyncData`

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

## Type

```ts [Signature]
function useAsyncData(
  key: string,
  handler: (nuxtApp?: NuxtApp) => Promise<DataT>,
  options?: AsyncDataOptions
): Promise<DataT>

type AsyncDataOptions = {
  server?: boolean
  lazy?: boolean
  default?: () => DataT | Ref<DataT>
  transform?: (input: DataT) => DataT
  pick?: string[]
  watch?: WatchSource[]
  initialCache?: boolean
}

type DataT = {
  data: Ref<DataT>
  pending: Ref<boolean>
  refresh: () => Promise<void>
  error: Ref<any>
}
```

## Params

* **key**: a unique key to ensure that data fetching can be properly de-duplicated across requests
* **handler**: an asynchronous function that returns a value
* **options**:
  * _lazy_: whether to resolve the async function after loading the route, instead of blocking navigation (defaults to `false`)
  * _default_: a factory function to set the default value of the data, before the async function resolves - particularly useful with the `lazy: true` option
  * _server_: whether to fetch the data on server-side (defaults to `true`)
  * _transform_: a function that can be used to alter `handler` function result after resolving
  * _pick_: only pick specified keys in this array from `handler` function result
  * _watch_: watch reactive sources to auto refresh
  * _initialCache_: When set to `false`, will skip payload cache for initial fetch. (defaults to `true`)
  * _default_: A function that returns the default value (before the handler function returns its value).

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.

## 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**: a function that can be used to refresh the data returned by the `handler` function
* **error**: an error object if the data fetching failed

By default, Nuxt waits until a `refresh` is finished before it can be executed again. Passing `true` as parameter skips that wait.

## Example

```ts
const { data, pending, error, refresh } = useAsyncData(
  'mountains',
  () => $fetch('https://api.nuxtjs.dev/mountains),
  {
    pick: ['title']
  }
)
```

::ReadMore{link="/guide/features/data-fetching"}
::