snapshot of https://github.com/TanStack/query.git (main, 2026-09-16; blobs > 131072B omitted)

examples/react/nextjs-app-optimistic-updates/app/api/todos/data.ts

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+export interface Todo {
+  id: string
+  text: string
+  createdAt: number
+}
+
+export const todos: Array<Todo> = [
+  {
+    id: crypto.randomUUID(),
+    text: 'Buy groceries',
+    createdAt: Date.now() - 3000,
+  },
+  {
+    id: crypto.randomUUID(),
+    text: 'Walk the dog',
+    createdAt: Date.now() - 2000,
+  },
+  {
+    id: crypto.randomUUID(),
+    text: 'Read a book',
+    createdAt: Date.now() - 1000,
+  },
+]
+
+export async function getTodos(): Promise<Array<Todo>> {
+  await new Promise((resolve) => setTimeout(resolve, 200))
+  return todos
+}

examples/react/nextjs-app-optimistic-updates/app/api/todos/route.ts

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+import { NextResponse } from 'next/server'
+import { todos, getTodos, type Todo } from './data'
+
+export async function GET() {
+  return NextResponse.json(await getTodos())
+}
+
+export async function POST(request: Request) {
+  let body: unknown
+  try {
+    body = await request.json()
+  } catch {
+    return NextResponse.json({ error: 'text is required' }, { status: 400 })
+  }
+
+  const text =
+    body !== null &&
+    typeof body === 'object' &&
+    'text' in body &&
+    typeof (body as { text: unknown }).text === 'string'
+      ? (body as { text: string }).text.trim()
+      : ''
+
+  if (!text) {
+    return NextResponse.json({ error: 'text is required' }, { status: 400 })
+  }
+
+  await new Promise((resolve) => setTimeout(resolve, 500))
+
+  if (Math.random() < 0.3) {
+    return NextResponse.json(
+      { error: 'Server error — please try again' },
+      { status: 500 },
+    )
+  }
+
+  const newTodo: Todo = {
+    id: crypto.randomUUID(),
+    text,
+    createdAt: Date.now(),
+  }
+
+  todos.push(newTodo)
+
+  return NextResponse.json(newTodo, { status: 201 })
+}

examples/react/nextjs-app-optimistic-updates/app/get-query-client.ts

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+import {
+  QueryClient,
+  defaultShouldDehydrateQuery,
+  environmentManager,
+} from '@tanstack/react-query'
+
+function makeQueryClient() {
+  return new QueryClient({
+    defaultOptions: {
+      queries: {
+        staleTime: 60 * 1000,
+      },
+      dehydrate: {
+        shouldDehydrateQuery: (query) =>
+          defaultShouldDehydrateQuery(query) ||
+          query.state.status === 'pending',
+      },
+    },
+  })
+}
+
+let browserQueryClient: QueryClient | undefined = undefined
+
+export function getQueryClient() {
+  if (environmentManager.isServer()) {
+    return makeQueryClient()
+  } else {
+    if (!browserQueryClient) browserQueryClient = makeQueryClient()
+    return browserQueryClient
+  }
+}

examples/react/nextjs-app-optimistic-updates/app/layout.tsx

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+import Providers from './providers'
+import type React from 'react'
+import type { Metadata } from 'next'
+
+export const metadata: Metadata = {
+  title: 'TanStack Query — Optimistic Updates',
+  description: 'Next.js App Router example with optimistic updates',
+}
+
+export default function RootLayout({
+  children,
+}: {
+  children: React.ReactNode
+}) {
+  return (
+    <html lang="en">
+      <body>
+        <Providers>{children}</Providers>
+      </body>
+    </html>
+  )
+}

examples/react/nextjs-app-optimistic-updates/app/page.tsx

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+import React from 'react'
+import { HydrationBoundary, dehydrate, noop } from '@tanstack/react-query'
+import { getQueryClient } from '@/app/get-query-client'
+import { getTodos } from '@/app/api/todos/data'
+import ApproachTabs from '@/components/ApproachTabs'
+
+export default function Home() {
+  const queryClient = getQueryClient()
+
+  void queryClient
+    .query({
+      queryKey: ['todos'],
+      queryFn: getTodos,
+    })
+    .catch(noop)
+
+  return (
+    <main style={{ maxWidth: 600, margin: '0 auto', padding: '2rem 1rem' }}>
+      <h1>Optimistic Updates with TanStack Query</h1>
+      <p style={{ color: '#666', marginBottom: '1.5rem' }}>
+        Add todos to see optimistic updates in action. The server randomly fails
+        ~30% of the time so you can observe automatic rollback.
+      </p>
+      <HydrationBoundary state={dehydrate(queryClient)}>
+        <ApproachTabs />
+      </HydrationBoundary>
+    </main>
+  )
+}

examples/react/nextjs-app-optimistic-updates/app/providers.tsx

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+'use client'
+import { QueryClientProvider } from '@tanstack/react-query'
+import { ReactQueryDevtools } from '@tanstack/react-query-devtools'
+import { getQueryClient } from '@/app/get-query-client'
+import type * as React from 'react'
+
+export default function Providers({ children }: { children: React.ReactNode }) {
+  const queryClient = getQueryClient()
+
+  return (
+    <QueryClientProvider client={queryClient}>
+      {children}
+      <ReactQueryDevtools />
+    </QueryClientProvider>
+  )
+}