tanstack-query

What this skill does

# TanStack Query (React Query) v5

**Status**: Production Ready ✅
**Last Updated**: 2025-10-22
**Dependencies**: React 18.0+, TypeScript 4.7+ (recommended)
**Latest Versions**: @tanstack/[email protected], @tanstack/[email protected]

---

## Quick Start (5 Minutes)

### 1. Install Dependencies

```bash
npm install @tanstack/react-query@latest
npm install -D @tanstack/react-query-devtools@latest
```

**Why this matters:**
- TanStack Query v5 requires React 18+ (uses useSyncExternalStore)
- DevTools are essential for debugging queries and mutations
- v5 has breaking changes from v4 - use latest for all fixes

### 2. Set Up QueryClient Provider

```tsx
// src/main.tsx or src/index.tsx
import { StrictMode } from 'react'
import { createRoot } from 'react-dom/client'
import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
import { ReactQueryDevtools } from '@tanstack/react-query-devtools'
import App from './App'

// Create a client
const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 1000 * 60 * 5, // 5 minutes
      gcTime: 1000 * 60 * 60, // 1 hour (formerly cacheTime)
      retry: 1,
      refetchOnWindowFocus: false,
    },
  },
})

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

**CRITICAL:**
- Wrap entire app with `QueryClientProvider`
- Configure `staleTime` to avoid excessive refetches (default is 0)
- Use `gcTime` (not `cacheTime` - renamed in v5)
- DevTools should be inside provider

### 3. Create First Query

```tsx
// src/hooks/useTodos.ts
import { useQuery } from '@tanstack/react-query'

type Todo = {
  id: number
  title: string
  completed: boolean
}

async function fetchTodos(): Promise<Todo[]> {
  const response = await fetch('/api/todos')
  if (!response.ok) {
    throw new Error('Failed to fetch todos')
  }
  return response.json()
}

export function useTodos() {
  return useQuery({
    queryKey: ['todos'],
    queryFn: fetchTodos,
  })
}

// Usage in component:
function TodoList() {
  const { data, isPending, isError, error } = useTodos()

  if (isPending) return <div>Loading...</div>
  if (isError) return <div>Error: {error.message}</div>

  return (
    <ul>
      {data.map(todo => (
        <li key={todo.id}>{todo.title}</li>
      ))}
    </ul>
  )
}
```

**CRITICAL:**
- v5 requires object syntax: `useQuery({ queryKey, queryFn })`
- Use `isPending` (not `isLoading` - that now means "pending AND fetching")
- Always throw errors in queryFn for proper error handling
- QueryKey should be array for consistent cache keys

### 4. Create First Mutation

```tsx
// src/hooks/useAddTodo.ts
import { useMutation, useQueryClient } from '@tanstack/react-query'

type NewTodo = {
  title: string
}

async function addTodo(newTodo: NewTodo) {
  const response = await fetch('/api/todos', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(newTodo),
  })
  if (!response.ok) throw new Error('Failed to add todo')
  return response.json()
}

export function useAddTodo() {
  const queryClient = useQueryClient()

  return useMutation({
    mutationFn: addTodo,
    onSuccess: () => {
      // Invalidate and refetch todos
      queryClient.invalidateQueries({ queryKey: ['todos'] })
    },
  })
}

// Usage in component:
function AddTodoForm() {
  const { mutate, isPending } = useAddTodo()

  const handleSubmit = (e: React.FormEvent<HTMLFormElement>) => {
    e.preventDefault()
    const formData = new FormData(e.currentTarget)
    mutate({ title: formData.get('title') as string })
  }

  return (
    <form onSubmit={handleSubmit}>
      <input name="title" required />
      <button type="submit" disabled={isPending}>
        {isPending ? 'Adding...' : 'Add Todo'}
      </button>
    </form>
  )
}
```

**Why this works:**
- Mutations use callbacks (`onSuccess`, `onError`, `onSettled`) - queries don't
- `invalidateQueries` triggers background refetch
- Mutations don't cache by default (correct behavior)

---

## The 7-Step Setup Process

### Step 1: Install Dependencies

```bash
# Core library (required)
npm install @tanstack/react-query

# DevTools (highly recommended for development)
npm install -D @tanstack/react-query-devtools

# Optional: ESLint plugin for best practices
npm install -D @tanstack/eslint-plugin-query
```

**Package roles:**
- `@tanstack/react-query` - Core React hooks and QueryClient
- `@tanstack/react-query-devtools` - Visual debugger (dev only, tree-shakeable)
- `@tanstack/eslint-plugin-query` - Catches common mistakes

**Version requirements:**
- React 18.0 or higher (uses `useSyncExternalStore`)
- TypeScript 4.7+ for best type inference (optional but recommended)

### Step 2: Configure QueryClient

```tsx
// src/lib/query-client.ts
import { QueryClient } from '@tanstack/react-query'

export const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      // How long data is considered fresh (won't refetch during this time)
      staleTime: 1000 * 60 * 5, // 5 minutes

      // How long inactive data stays in cache before garbage collection
      gcTime: 1000 * 60 * 60, // 1 hour (v5: renamed from cacheTime)

      // Retry failed requests (0 on server, 3 on client by default)
      retry: (failureCount, error) => {
        if (error instanceof Response && error.status === 404) return false
        return failureCount < 3
      },

      // Refetch on window focus (can be annoying during dev)
      refetchOnWindowFocus: false,

      // Refetch on network reconnect
      refetchOnReconnect: true,

      // Refetch on component mount if data is stale
      refetchOnMount: true,
    },
    mutations: {
      // Retry mutations on failure (usually don't want this)
      retry: 0,
    },
  },
})
```

**Key configuration decisions:**

**staleTime vs gcTime:**
- `staleTime`: How long until data is considered "stale" and might refetch
  - `0` (default): Data is immediately stale, refetches on mount/focus
  - `1000 * 60 * 5`: Data fresh for 5 min, no refetch during this time
  - `Infinity`: Data never stale, manual invalidation only
- `gcTime`: How long unused data stays in cache
  - `1000 * 60 * 5` (default): 5 minutes
  - `Infinity`: Never garbage collect (memory leak risk)

**When to refetch:**
- `refetchOnWindowFocus: true` - Good for frequently changing data (stock prices)
- `refetchOnWindowFocus: false` - Good for stable data or during development
- `refetchOnMount: true` - Ensures fresh data when component mounts
- `refetchOnReconnect: true` - Refetch after network reconnect

### Step 3: Wrap App with Provider

```tsx
// src/main.tsx
import { StrictMode } from 'react'
import { createRoot } from 'react-dom/client'
import { QueryClientProvider } from '@tanstack/react-query'
import { ReactQueryDevtools } from '@tanstack/react-query-devtools'
import { queryClient } from './lib/query-client'
import App from './App'

createRoot(document.getElementById('root')!).render(
  <StrictMode>
    <QueryClientProvider client={queryClient}>
      <App />
      <ReactQueryDevtools
        initialIsOpen={false}
        buttonPosition="bottom-right"
      />
    </QueryClientProvider>
  </StrictMode>
)
```

**Provider placement:**
- Must wrap all components that use TanStack Query hooks
- DevTools must be inside provider
- Only one QueryClient instance for entire app

**DevTools configuration:**
- `initialIsOpen={false}` - Collapsed by default
- `buttonPosition="bottom-right"` - Where to show toggle button
- Automatically removed in production builds (tree-shaken)

### Step 4: Create Custom Query Hooks

**Pattern: Reusable Query Hooks**

```tsx
// src/api/todos.ts - API functions
export type Todo = {
  id: number
  title: string
  completed: boolean
}

export async function fetchTodos(): Promise<Todo[]> {
  const response = await fetch('/api/todos')
  if