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

title	description
Component Options	Learn how to migrate from Nuxt 2 components options to Nuxt 3 composables.

asyncData and fetch

Nuxt 3 provides new options for fetching data from an API.

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 or $fetch method which is using unjs/ofetch. It has a number of benefits, including:

1. It will handle 'smartly' making 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 or fetching data.

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:

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:

<script setup lang="ts">
// 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.

::note 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.
2. Replace the fetch hook with useAsyncData or useFetch in your component.

head

:read-more{to="/docs/migration/meta"}

key

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

- <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>

layout

:read-more{to="/docs/migration/pages-and-layouts"}

loading

This feature is not yet supported in Nuxt 3.

middleware

:read-more{to="/docs/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) for more info. Similar to key, specify it within the definePageMeta compiler macro.

- <script>
- export default {
-   scrollToTop: false
- }
+ <script setup>
+ definePageMeta({
+   scrollToTop: false
+ })
</script>

transition

:read-more{to="/docs/getting-started/transitions"}

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).

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

watchQuery

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

<script setup lang="ts">
const route = useRoute()
const { data, refresh } = await useFetch('/api/user')
watch(() => route.query, () => refresh())
</script>