Nuxt/docs/content/7.migration/7.component-options.md

# Component Options

## `asyncData` and `fetch` component options

Nuxt 3 provides new options for [fetching data from an API](/getting-started/data-fetching).

<!-- TODO: Intro to <script setup> -->
<!-- TODO: Mention about options compatibility with asyncData -->

### Isomorphic Fetch

In Nuxt 2 you might use `@nuxtjs/axios` or `@nuxt/http` to fetch your data - or just the polyfilled global `fetch`.

In Nuxt 3 you can use a globally available `fetch` method that has the same API as [the Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch) or `$fetch` method which is using [unjs/ohmyfetch](https://github.com/unjs/ohmyfetch). It has a number of benefits, including:

1. It will handle 'smartly' making [direct API calls](/guide/concepts/server-engine#direct-api-calls) if it's running on the server, or making a client-side call to your API if it's running on the client. (It can also handle calling third-party APIs.)

2. Plus, it comes with convenience features including automatically parsing responses and stringifying data.

You can read more [about direct API calls](/guide/concepts/server-engine#direct-api-calls) or [fetching data](/getting-started/data-fetching).

### Using Composables

Nuxt 3 provides new composables for fetching data: `useAsyncData` and `useFetch`. They each have 'lazy' variants (`useLazyAsyncData` and `useLazyFetch`), which do not block client-side navigation.

In Nuxt 2, you'd fetch your data in your component using a syntax similar to:

```ts
export default {
  async asyncData({ params, $http }) {
    const post = await $http.$get(`https://api.nuxtjs.dev/posts/${params.id}`)
    return { post }
  },
  // or alternatively
  fetch () {
    this.post = await $http.$get(`https://api.nuxtjs.dev/posts/${params.id}`)
  }
}
```

Within your methods and templates, you could use the `post` variable similar how you'd use any other piece of data provided by your component.

With Nuxt 3, you can perform this data fetching using composables in your `setup()` method or `<script setup>` tag:

```vue
<script setup>
  // Define params wherever, through `defineProps()`, `useRoute()`, etc.
  const { data: post, refresh } = await useAsyncData('post', () => $fetch(`https://api.nuxtjs.dev/posts/${params.id}`) )
  // Or instead - useFetch is a convenience wrapper around useAsyncData when you're just performing a simple fetch
  const { data: post, refresh } = await useFetch(`https://api.nuxtjs.dev/posts/${params.id}`)
</script>
```

You can now use `post` inside of your Nuxt 3 template, or call `refresh` to update the data.

::alert{type=info}
Despite the names, `useFetch` is not a direct replacement of the `fetch()` hook. Rather, `useAsyncData` replaces both hooks and is more customizable; it can do more than simply fetching data from an endpoint. `useFetch` is a convenience wrapper around `useAsyncData` for simply fetching data from an endpoint.
::

### Migration

1. Replace the `asyncData` hook with `useAsyncData` or `useFetch` in your page/component.
1. Replace the `fetch` hook with `useAsyncData` or `useFetch` in your component.

## `head`

See [meta tag migration](/migration/meta).

## `key`

You can now define a key within the `definePageMeta` compiler macro.

```diff [pages/index.vue]
- <script>
- export default {
-   key: 'index'
-   // or a method
-   // key: route => route.fullPath
- }
+ <script setup>
+ definePageMeta({
+   key: 'index'
+   // or a method
+   // key: route => route.fullPath
+ })
  </script>
```

### Migration

1. Migrate `key` from component options to `definePageMeta`.

## `layout`

See [layout migration](/migration/pages-and-layouts).

## `loading`

This feature is not yet supported in Nuxt 3.

## `middleware`

See [middleware migration](/migration/plugins-and-middleware).

## `scrollToTop`

This feature is not yet supported in Nuxt 3. If you want to overwrite the default scroll behavior of `vue-router`, you can do so in `~/app/router.options.ts` (see [docs](/guide/directory-structure/pages/#router-options)) for more info.

## `transition`

See [layout migration](/migration/pages-and-layouts).

## `validate`

The validate hook in Nuxt 3 only accepts a single argument, the `route`. Just as in Nuxt 2, you can return a boolean value. If you return false and another match can't be found, this will mean a 404. You can also directly return an object with `statusCode`/`statusMessage` to respond immediately with an error (other matches will not be checked).

```diff [pages/users/[id].vue]
- <script>
- export default {
-   async validate({ params }) {
-     return /^\d+$/.test(params.id)
-   }
- }
+ <script setup>
+ definePageMeta({
+   validate: async (route) => {
+     const nuxtApp = useNuxtApp()
+     return /^\d+$/.test(params.id)
+   }
+ })
  </script>
```

## `watchQuery`

This is not supported in Nuxt 3. Instead, you can directly use a watcher to trigger refetching data.

```vue [pages/users/[id].vue]
<script setup>
const route = useRoute()
const { data, refresh } = await useFetch('/api/user')
watch(() => route.query, () => refresh())
</script>
```