mydot/agents/.agents/skills/nuxt/references/core-data-fetching.md

name, description

name	description
data-fetching	useFetch, useAsyncData, and $fetch for SSR-friendly data fetching

Data Fetching

Nuxt provides composables for SSR-friendly data fetching that prevent double-fetching and handle hydration.

Overview

• $fetch - Basic fetch utility (use for client-side events)
• useFetch - SSR-safe wrapper around $fetch (use for component data)
• useAsyncData - SSR-safe wrapper for any async function
• createUseFetch / createUseAsyncData - factories to build typed custom composables with baked-in defaults

useFetch

Primary composable for fetching data in components:

<script setup lang="ts">
const { data, status, error, refresh, clear } = await useFetch('/api/posts')
</script>

<template>
  <div v-if="status === 'pending'">Loading...</div>
  <div v-else-if="error">Error: {{ error.message }}</div>
  <div v-else>
    <article v-for="post in data" :key="post.id">
      {{ post.title }}
    </article>
  </div>
</template>

With Options

const { data } = await useFetch('/api/posts', {
  // Query parameters
  query: { page: 1, limit: 10 },
  // Request body (for POST/PUT)
  body: { title: 'New Post' },
  // HTTP method
  method: 'POST',
  // Only pick specific fields
  pick: ['id', 'title'],
  // Transform response
  transform: (posts) => posts.map(p => ({ ...p, slug: slugify(p.title) })),
  // Custom key for caching
  key: 'posts-list',
  // Don't fetch on server
  server: false,
  // Don't block navigation
  lazy: true,
  // Don't fetch immediately
  immediate: false,
  // Default value
  default: () => [],
})

Reactive Parameters

<script setup lang="ts">
const page = ref(1)
const { data } = await useFetch('/api/posts', {
  query: { page }, // Automatically refetches when page changes
})
</script>

Computed URL

<script setup lang="ts">
const id = ref(1)
const { data } = await useFetch(() => `/api/posts/${id.value}`)
// Refetches when id changes
</script>

useAsyncData

For wrapping any async function:

<script setup lang="ts">
const { data, error } = await useAsyncData('user', () => {
  return myCustomFetch('/user/profile')
})
</script>

Multiple Requests

<script setup lang="ts">
const { data } = await useAsyncData('cart', async () => {
  const [coupons, offers] = await Promise.all([
    $fetch('/api/coupons'),
    $fetch('/api/offers'),
  ])
  return { coupons, offers }
})
</script>

Custom Fetchers: createUseFetch / createUseAsyncData

Factory macros that produce a fully typed custom composable with pre-defined options. Must be an exported declaration inside app/composables/ (Nuxt injects dedup keys at build time).

// app/composables/useAPI.ts
export const useAPI = createUseFetch({
  baseURL: 'https://api.nuxt.com',
  // shared interceptors, headers, etc.
  onResponseError({ response }) {
    if (response.status === 401) navigateTo('/login')
  },
})

<script setup lang="ts">
// Same signature/return as useFetch, with defaults applied
const { data } = await useAPI('/modules')
// Caller can still override any option
const { data: other } = await useAPI('/modules', { baseURL: 'https://other.com' })
</script>

Default vs Override mode:

// Plain object → options act as DEFAULTS (caller can override)
export const useAPI = createUseFetch({ baseURL: '/api', lazy: true })

// Function → options OVERRIDE caller's (enforce auth/baseURL)
export const useAPI = createUseFetch(callerOptions => ({
  baseURL: 'https://api.nuxt.com', // always enforced
}))

Use the function form when you need useNuxtApp() (called in setup context, not module scope):

// app/composables/useAPI.ts
export const useAPI = createUseFetch(callerOptions => ({
  $fetch: useNuxtApp().$api as typeof $fetch,
  ...callerOptions,
}))

createUseAsyncData works identically for wrapping arbitrary async functions:

// app/composables/useCachedData.ts
export const useCachedData = createUseAsyncData({
  getCachedData(key, nuxtApp) {
    return nuxtApp.payload.data[key] ?? nuxtApp.static.data[key]
  },
})

Replaces the old "don't await your custom useFetch wrapper" caveat — use these factories instead of hand-rolled wrappers.

$fetch

For client-side events (form submissions, button clicks):

<script setup lang="ts">
async function submitForm() {
  const result = await $fetch('/api/submit', {
    method: 'POST',
    body: { name: 'John' },
  })
}
</script>

Important: Don't use $fetch alone in setup for initial data - it will fetch twice (server + client). Use useFetch or useAsyncData instead.

Return Values

All composables return:

Property	Type	Description
data	Ref<T>	Fetched data (undefined until resolved)
error	Ref<Error>	Error if request failed
status	Ref<'idle' | 'pending' | 'success' | 'error'>	Request status
pending	Ref<boolean>	Whether a request is in progress
refresh	() => Promise	Refetch data
execute	() => Promise	Alias for refresh
clear	() => void	Reset to default/idle and cancel pending requests

Prefer status over pending for fine-grained state. useFetch no longer accepts a top-level timeout option (still available on useAsyncData); use a cache option ('default', 'no-store', false, etc.) for Fetch cache control.

Lazy Fetching

Don't block navigation:

<script setup lang="ts">
// Using lazy option
const { data, status } = await useFetch('/api/posts', { lazy: true })

// Or use lazy variants
const { data, status } = await useLazyFetch('/api/posts')
const { data, status } = await useLazyAsyncData('key', fetchFn)
</script>

Refresh & Watch

<script setup lang="ts">
const category = ref('tech')

const { data, refresh } = await useFetch('/api/posts', {
  query: { category },
  // Auto-refresh when category changes
  watch: [category],
})

// Manual refresh
const refreshData = () => refresh()
</script>

Caching

Data is cached by key. Share data across components:

<script setup lang="ts">
// In component A
const { data } = await useFetch('/api/user', { key: 'current-user' })

// In component B - uses cached data
const { data } = useNuxtData('current-user')
</script>

Refresh cached data globally:

// Refresh specific key
await refreshNuxtData('current-user')

// Refresh all data
await refreshNuxtData()

// Clear cached data
clearNuxtData('current-user')

Interceptors

const { data } = await useFetch('/api/auth', {
  onRequest({ options }) {
    options.headers.set('Authorization', `Bearer ${token}`)
  },
  onRequestError({ error }) {
    console.error('Request failed:', error)
  },
  onResponse({ response }) {
    // Process response
  },
  onResponseError({ response }) {
    if (response.status === 401) {
      navigateTo('/login')
    }
  },
})

Passing Headers (SSR)

useFetch automatically proxies cookies/headers from client to server. For $fetch:

<script setup lang="ts">
const headers = useRequestHeaders(['cookie'])
const data = await $fetch('/api/user', { headers })
</script>