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

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# 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> -->
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### 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/ofetch](https://github.com/unjs/ofetch). 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>
```