React Data Fetching

React Data Fetching Patterns

Table of Contents

• When to Use
• Instructions
• Details
• Source

Production-ready patterns for fetching, caching, and synchronizing server data in React applications. These patterns are framework-agnostic — they work whether you're using Vite + React Router, Next.js, Remix, or a custom setup.

When to Use

Reference these patterns when:

• Adding data fetching to components
• Replacing useEffect + fetch with a proper data layer
• Implementing caching, deduplication, or optimistic updates
• Debugging waterfall loading patterns
• Choosing between data fetching libraries

Instructions

• Apply these patterns during code generation, review, and refactoring. When you see fetch-in-effect without caching or deduplication, suggest the appropriate pattern.

Details

Overview

The most common performance problem in React apps is request waterfalls — sequential fetches that could run in parallel. The second most common problem is redundant fetches — multiple components fetching the same data independently. The patterns below address both, starting with the highest-impact fixes.

1. Parallelize Independent Fetches with Promise.all

Impact: CRITICAL — Eliminates sequential waterfalls for 2-10x improvement.

When multiple fetches have no dependencies on each other, run them concurrently.

Avoid — sequential (3 round trips):

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async function loadDashboard() {
  const user = await fetchUser()
  const posts = await fetchPosts()
  const notifications = await fetchNotifications()
  return { user, posts, notifications }
}

Prefer — parallel (1 round trip):

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async function loadDashboard() {
  const [user, posts, notifications] = await Promise.all([
    fetchUser(),
    fetchPosts(),
    fetchNotifications(),
  ])
  return { user, posts, notifications }
}

When fetches have partial dependencies (B depends on A, but C doesn't), start independent work immediately:

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async function loadPage() {
  const userPromise = fetchUser()
  const configPromise = fetchConfig()

  const user = await userPromise
  const [config, posts] = await Promise.all([
    configPromise,
    fetchPosts(user.id), // depends on user
  ])
  return { user, config, posts }
}

2. Defer Await Until the Value Is Needed

Impact: HIGH — Starts work earlier without blocking on results you don't need yet.

A common mistake is to await each promise immediately, even when subsequent code doesn't need the result right away. Start the promise early, then await it at the point where you actually read the value.

Avoid — blocks unnecessarily:

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async function loadProfile(userId: string) {
  const user = await fetchUser(userId)       // waits here
  const prefs = await fetchPreferences()     // starts only after user resolves
  const avatar = buildAvatarUrl(user.avatar)
  return { user, prefs, avatar }
}

Prefer — start early, await late:

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async function loadProfile(userId: string) {
  const userPromise = fetchUser(userId)      // starts immediately
  const prefsPromise = fetchPreferences()    // starts immediately

  const user = await userPromise             // await when needed
  const avatar = buildAvatarUrl(user.avatar)
  const prefs = await prefsPromise           // may already be resolved

  return { user, prefs, avatar }
}

This is complementary to Promise.all — use defer-await when you need intermediate results between fetches, and Promise.all when you can wait for everything at once.

3. Use TanStack Query for Client-Side Data

Impact: CRITICAL — Automatic caching, deduplication, revalidation, and error handling.

Raw useEffect + fetch lacks caching, deduplication, retry, and background refresh. Use a data fetching library.

Avoid — no caching, no dedup, no error handling:

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function UserProfile({ userId }: { userId: string }) {
  const [user, setUser] = useState<User | null>(null)
  const [loading, setLoading] = useState(true)

  useEffect(() => {
    setLoading(true)
    fetch(`/api/users/${userId}`)
      .then(r => r.json())
      .then(setUser)
      .finally(() => setLoading(false))
  }, [userId])

  if (loading) return <Skeleton />
  return <div>{user?.name}</div>
}

Prefer — TanStack Query (recommended for Vite + React apps):

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import { useQuery } from '@tanstack/react-query'

function UserProfile({ userId }: { userId: string }) {
  const { data: user, isLoading } = useQuery({
    queryKey: ['user', userId],
    queryFn: () => fetch(`/api/users/${userId}`).then(r => r.json()),
  })

  if (isLoading) return <Skeleton />
  return <div>{user?.name}</div>
}

TanStack Query is the strongest choice for Vite apps — it's framework-agnostic, has built-in useSuspenseQuery, devtools, infinite queries, optimistic mutations, and offline support. SWR is a lighter alternative that covers the basics (dedup, caching, revalidation) but has fewer features for complex mutation workflows.

Both give you: request deduplication, stale-while-revalidate caching, automatic retries, and background refresh.

Setup for Vite apps:

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// main.tsx
import { QueryClient, QueryClientProvider } from '@tanstack/react-query'

const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 60_000, // 1 minute
      retry: 2,
    },
  },
})

createRoot(document.getElementById('root')!).render(
  <QueryClientProvider client={queryClient}>
    <App />
  </QueryClientProvider>
)

4. Use Suspense for Declarative Loading States

Impact: HIGH — Cleaner code, automatic loading coordination, streaming support.

Suspense lets you declare loading boundaries in the component tree instead of managing isLoading state in every component.

Avoid — manual loading orchestration:

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function Dashboard() {
  const { data: user, isLoading: userLoading } = useQuery(userQuery)
  const { data: stats, isLoading: statsLoading } = useQuery(statsQuery)

  if (userLoading || statsLoading) return <FullPageSpinner />
  return (
    <div>
      <UserHeader user={user} />
      <StatsPanel stats={stats} />
    </div>
  )
}

Prefer — Suspense boundaries:

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function Dashboard() {
  return (
    <Suspense fallback={<FullPageSpinner />}>
      <DashboardContent />
    </Suspense>
  )
}

function DashboardContent() {
  const { data: user } = useSuspenseQuery(userQuery)
  const { data: stats } = useSuspenseQuery(statsQuery)
  return (
    <div>
      <UserHeader user={user} />
      <StatsPanel stats={stats} />
    </div>
  )
}

For independent sections, use separate Suspense boundaries so they load independently:

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function Dashboard() {
  return (
    <div>
      <Suspense fallback={<HeaderSkeleton />}>
        <UserHeader />
      </Suspense>
      <Suspense fallback={<StatsSkeleton />}>
        <StatsPanel />
      </Suspense>
    </div>
  )
}

TanStack Query provides useSuspenseQuery and SWR provides { suspense: true } option.

5. Prefetch Data Before Navigation

Impact: HIGH — Eliminates loading states on page transitions.

Start fetching data before the user commits to a navigation — on hover, focus, or route preload.

With TanStack Query:

tsxCopy code
import { useQueryClient } from '@tanstack/react-query'

function ProjectLink({ projectId }: { projectId: string }) {
  const queryClient = useQueryClient()

  const prefetch = () => {
    queryClient.prefetchQuery({
      queryKey: ['project', projectId],
      queryFn: () => fetchProject(projectId),
      staleTime: 30_000,
    })
  }

  return (
    <Link
      to={`/projects/${projectId}`}
      onMouseEnter={prefetch}
      onFocus={prefetch}
    >
      View Project
    </Link>
  )
}

With React Router loaders (Vite apps):

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// routes.tsx
const routes = [
  {
    path: '/projects/:id',
    loader: ({ params }) => queryClient.ensureQueryData({
      queryKey: ['project', params.id],
      queryFn: () => fetchProject(params.id!),
    }),
    Component: ProjectPage,
  },
]

6. Use React.cache() for Server-Side Deduplication

Impact: MEDIUM — Deduplicates expensive operations within a single server render.

In server components (RSC), React.cache() ensures the same async call made by multiple components only executes once per request.

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import { cache } from 'react'

export const getSession = cache(async () => {
  const session = await auth()
  if (!session?.user?.id) return null
  return session
})

export const getUser = cache(async (userId: string) => {
  return await db.user.findUnique({ where: { id: userId } })
})

Multiple components calling getSession() in the same render share one execution.

Important: Use primitive arguments (strings, numbers) for cache keys. Inline objects create new references and cause cache misses:

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// Cache miss every time — new object reference
getUser({ id: '123' })
getUser({ id: '123' }) // miss

// Cache hit — same string value
getUser('123')
getUser('123') // hit

7. Implement Optimistic Updates for Instant Feedback

Impact: HIGH — UI responds immediately without waiting for the server.

For mutations where the outcome is predictable (toggling a like, updating a name), update the UI instantly and reconcile with the server response.

With TanStack Query:

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import { useMutation, useQueryClient } from '@tanstack/react-query'

function LikeButton({ postId }: { postId: string }) {
  const queryClient = useQueryClient()

  const { mutate: toggleLike } = useMutation({
    mutationFn: () => fetch(`/api/posts/${postId}/like`, { method: 'POST' }),
    onMutate: async () => {
      await queryClient.cancelQueries({ queryKey: ['post', postId] })
      const previous = queryClient.getQueryData<Post>(['post', postId])
      queryClient.setQueryData<Post>(['post', postId], old => ({
        ...old!,
        liked: !old!.liked,
        likeCount: old!.liked ? old!.likeCount - 1 : old!.likeCount + 1,
      }))
      return { previous }
    },
    onError: (_err, _vars, context) => {
      queryClient.setQueryData(['post', postId], context?.previous)
    },
    onSettled: () => {
      queryClient.invalidateQueries({ queryKey: ['post', postId] })
    },
  })

  return <button onClick={() => toggleLike()}>Like</button>
}

8. Avoid Fetch Waterfalls in Component Trees

Impact: CRITICAL — Parent-then-child fetching is the #1 performance problem.

When a parent fetches data and a child fetches its own data based on the parent's result, you create a waterfall. Restructure to fetch in parallel.

Avoid — child can't start until parent finishes:

tsxCopy code
function UserPage({ userId }: { userId: string }) {
  const { data: user } = useQuery({
    queryKey: ['user', userId],
    queryFn: () => fetchUser(userId),
  })

  if (!user) return <Skeleton />
  return <UserPosts userId={user.id} /> // starts fetching only after user loads
}

function UserPosts({ userId }: { userId: string }) {
  const { data: posts } = useQuery({
    queryKey: ['posts', userId],
    queryFn: () => fetchPosts(userId),
  })
  // ...
}

Prefer — fetch both at the same level:

tsxCopy code
function UserPage({ userId }: { userId: string }) {
  const { data: user } = useQuery({
    queryKey: ['user', userId],
    queryFn: () => fetchUser(userId),
  })
  const { data: posts } = useQuery({
    queryKey: ['posts', userId],
    queryFn: () => fetchPosts(userId),
  })

  if (!user) return <Skeleton />
  return (
    <div>
      <UserHeader user={user} />
      <PostList posts={posts ?? []} />
    </div>
  )
}

Or use a route-level loader to fetch all data before the component renders.

9. Deduplicate Global Event Listeners

Impact: MEDIUM — Prevents N listeners for N component instances.

When multiple component instances need the same global event (resize, scroll, online), share a single listener.

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// hooks/useOnlineStatus.ts
import { useSyncExternalStore } from 'react'

function subscribe(callback: () => void) {
  window.addEventListener('online', callback)
  window.addEventListener('offline', callback)
  return () => {
    window.removeEventListener('online', callback)
    window.removeEventListener('offline', callback)
  }
}

function getSnapshot() {
  return navigator.onLine
}

export function useOnlineStatus() {
  return useSyncExternalStore(subscribe, getSnapshot, () => true)
}

useSyncExternalStore automatically deduplicates subscriptions and ensures consistent state across concurrent renders.

10. Use Passive Event Listeners for Scroll and Touch

Impact: LOW-MEDIUM — Prevents scroll jank from blocking listeners.

Non-passive scroll/touch listeners block the browser's compositor thread. Mark them passive when you don't call preventDefault().

Avoid — blocks scrolling:

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useEffect(() => {
  const handler = () => trackScroll(window.scrollY)
  window.addEventListener('scroll', handler)
  return () => window.removeEventListener('scroll', handler)
}, [])

Prefer — non-blocking:

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useEffect(() => {
  const handler = () => trackScroll(window.scrollY)
  window.addEventListener('scroll', handler, { passive: true })
  return () => window.removeEventListener('scroll', handler)
}, [])

11. Schema-Version Your Client Storage

Impact: LOW-MEDIUM — Prevents crashes from stale localStorage data.

When reading from localStorage or sessionStorage, stale data from a previous app version can crash your app. Add a schema version and validate.

Avoid — crashes on schema change:

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const [prefs, setPrefs] = useState(() => {
  return JSON.parse(localStorage.getItem('prefs') || '{}')
})

Prefer — versioned with fallback:

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const PREFS_VERSION = 2

const [prefs, setPrefs] = useState<Prefs>(() => {
  try {
    const raw = localStorage.getItem('prefs')
    if (!raw) return DEFAULT_PREFS
    const parsed = JSON.parse(raw)
    if (parsed._v !== PREFS_VERSION) return DEFAULT_PREFS
    return parsed
  } catch {
    return DEFAULT_PREFS
  }
})

// On save, include version
useEffect(() => {
  localStorage.setItem('prefs', JSON.stringify({ ...prefs, _v: PREFS_VERSION }))
}, [prefs])

Source

Patterns from patterns.dev — framework-agnostic React data fetching guidance for the broader web engineering community.