tanstack-query

What this skill does

# TanStack Query (React Query) v5

**Last Updated**: 2026-01-20
**Versions**: @tanstack/[email protected], @tanstack/[email protected]
**Requires**: React 18.0+ (useSyncExternalStore), TypeScript 4.7+ (recommended)

---

## v5 New Features

### useMutationState - Cross-Component Mutation Tracking

Access mutation state from anywhere without prop drilling:

```tsx
import { useMutationState } from '@tanstack/react-query'

function GlobalLoadingIndicator() {
  // Get all pending mutations
  const pendingMutations = useMutationState({
    filters: { status: 'pending' },
    select: (mutation) => mutation.state.variables,
  })

  if (pendingMutations.length === 0) return null
  return <div>Saving {pendingMutations.length} items...</div>
}

// Filter by mutation key
const todoMutations = useMutationState({
  filters: { mutationKey: ['addTodo'] },
})
```

### Simplified Optimistic Updates

New pattern using `variables` - no cache manipulation, no rollback needed:

```tsx
function TodoList() {
  const { data: todos } = useQuery({ queryKey: ['todos'], queryFn: fetchTodos })

  const addTodo = useMutation({
    mutationKey: ['addTodo'],
    mutationFn: (newTodo) => api.addTodo(newTodo),
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: ['todos'] })
    },
  })

  // Show optimistic UI using variables from pending mutations
  const pendingTodos = useMutationState({
    filters: { mutationKey: ['addTodo'], status: 'pending' },
    select: (mutation) => mutation.state.variables,
  })

  return (
    <ul>
      {todos?.map(todo => <li key={todo.id}>{todo.title}</li>)}
      {/* Show pending items with visual indicator */}
      {pendingTodos.map((todo, i) => (
        <li key={`pending-${i}`} style={{ opacity: 0.5 }}>{todo.title}</li>
      ))}
    </ul>
  )
}
```

### throwOnError - Error Boundaries

Renamed from `useErrorBoundary` (breaking change):

```tsx
import { QueryErrorResetBoundary } from '@tanstack/react-query'
import { ErrorBoundary } from 'react-error-boundary'

function App() {
  return (
    <QueryErrorResetBoundary>
      {({ reset }) => (
        <ErrorBoundary onReset={reset} fallbackRender={({ resetErrorBoundary }) => (
          <div>
            Error! <button onClick={resetErrorBoundary}>Retry</button>
          </div>
        )}>
          <Todos />
        </ErrorBoundary>
      )}
    </QueryErrorResetBoundary>
  )
}

function Todos() {
  const { data } = useQuery({
    queryKey: ['todos'],
    queryFn: fetchTodos,
    throwOnError: true, // ✅ v5 (was useErrorBoundary in v4)
  })
  return <div>{data.map(...)}</div>
}
```

### Network Mode (Offline/PWA Support)

Control behavior when offline:

```tsx
const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      networkMode: 'offlineFirst', // Use cache when offline
    },
  },
})

// Per-query override
useQuery({
  queryKey: ['todos'],
  queryFn: fetchTodos,
  networkMode: 'always', // Always try, even offline (for local APIs)
})
```

| Mode | Behavior |
|------|----------|
| `online` (default) | Only fetch when online |
| `always` | Always try (useful for local/service worker APIs) |
| `offlineFirst` | Use cache first, fetch when online |

**Detecting paused state:**
```tsx
const { isPending, fetchStatus } = useQuery(...)
// isPending + fetchStatus === 'paused' = offline, waiting for network
```

### useQueries with Combine

Combine results from parallel queries:

```tsx
const results = useQueries({
  queries: userIds.map(id => ({
    queryKey: ['user', id],
    queryFn: () => fetchUser(id),
  })),
  combine: (results) => ({
    data: results.map(r => r.data),
    pending: results.some(r => r.isPending),
    error: results.find(r => r.error)?.error,
  }),
})

// Access combined result
if (results.pending) return <Loading />
console.log(results.data) // [user1, user2, user3]
```

### infiniteQueryOptions Helper

Type-safe factory for infinite queries (parallel to `queryOptions`):

```tsx
import { infiniteQueryOptions, useInfiniteQuery, prefetchInfiniteQuery } from '@tanstack/react-query'

const todosInfiniteOptions = infiniteQueryOptions({
  queryKey: ['todos', 'infinite'],
  queryFn: ({ pageParam }) => fetchTodosPage(pageParam),
  initialPageParam: 0,
  getNextPageParam: (lastPage) => lastPage.nextCursor,
})

// Reuse across hooks
useInfiniteQuery(todosInfiniteOptions)
useSuspenseInfiniteQuery(todosInfiniteOptions)
prefetchInfiniteQuery(queryClient, todosInfiniteOptions)
```

### maxPages - Memory Optimization

Limit pages stored in cache for infinite queries:

```tsx
useInfiniteQuery({
  queryKey: ['posts'],
  queryFn: ({ pageParam }) => fetchPosts(pageParam),
  initialPageParam: 0,
  getNextPageParam: (lastPage) => lastPage.nextCursor,
  getPreviousPageParam: (firstPage) => firstPage.prevCursor, // Required with maxPages
  maxPages: 3, // Only keep 3 pages in memory
})
```

**Note:** `maxPages` requires bi-directional pagination (`getNextPageParam` AND `getPreviousPageParam`).

---

## Quick Setup

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

### Step 2: Provider + Config

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

const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 1000 * 60 * 5, // 5 min
      gcTime: 1000 * 60 * 60, // 1 hour (v5: renamed from cacheTime)
      refetchOnWindowFocus: false,
    },
  },
})

<QueryClientProvider client={queryClient}>
  <App />
  <ReactQueryDevtools initialIsOpen={false} />
</QueryClientProvider>
```

### Step 3: Query + Mutation Hooks

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

// Query options factory (v5 pattern)
export const todosQueryOptions = queryOptions({
  queryKey: ['todos'],
  queryFn: async () => {
    const res = await fetch('/api/todos')
    if (!res.ok) throw new Error('Failed to fetch')
    return res.json()
  },
})

export function useTodos() {
  return useQuery(todosQueryOptions)
}

export function useAddTodo() {
  const queryClient = useQueryClient()
  return useMutation({
    mutationFn: async (newTodo) => {
      const res = await fetch('/api/todos', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(newTodo),
      })
      if (!res.ok) throw new Error('Failed to add')
      return res.json()
    },
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: ['todos'] })
    },
  })
}

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

  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 Rules

### Always Do

✅ **Use object syntax for all hooks**
```tsx
// v5 ONLY supports this:
useQuery({ queryKey, queryFn, ...options })
useMutation({ mutationFn, ...options })
```

✅ **Use array query keys**
```tsx
queryKey: ['todos']              // List
queryKey: ['todos', id]          // Detail
queryKey: ['todos', { filter }]  // Filtered
```

✅ **Configure staleTime appropriately**
```tsx
staleTime: 1000 * 60 * 5 // 5 min - prevents excessive refetches
```

✅ **Use isPending for initial loading state**
```tsx
if (isPending) return <Loading />
// isPending = no data yet AND fetching
```

✅ **Throw errors in queryFn**
```tsx
if (!response.ok) throw new Error('Failed')
```

✅ **Invalidate queries after mutations**
```tsx
onSuccess: () => {
  queryClient.invalidateQueries({ queryKey: ['todos'] })
}
```

✅ **Use queryOptions factory for reusable patterns**
```tsx
const opts = queryOptions({ queryKey, queryFn })
useQuery(opts)
useSuspenseQuery(opts)
prefetchQuery(opts)
```

✅ **Use gcTime (not cacheTime)**
```tsx
gc