--- name: web-state-redux-toolkit description: Redux Toolkit patterns for complex client state. Use when managing enterprise-scale state, needing DevTools, entity normalization, or RTK Query for data fetching. --- # Redux Toolkit Patterns > **Quick Guide:** Use Redux Toolkit for complex client state requiring DevTools, middleware, or entity normalization. Use RTK Query for data fetching with caching. For simpler UI state, a lighter state management solution may be more appropriate. NEVER use legacy Redux patterns (createStore, combineReducers manually, switch statements in reducers). **Detailed Resources:** - For code examples, see [examples/](examples/) folder: - [core.md](examples/core.md) - Store setup, slices - [typed-hooks.md](examples/typed-hooks.md) - Type-safe hooks - [rtk-query.md](examples/rtk-query.md) - Data fetching - [entity-adapters.md](examples/entity-adapters.md) - Normalized state - [async-thunks.md](examples/async-thunks.md) - Async operations - [selectors.md](examples/selectors.md) - Memoized selectors - [rtk-2-features.md](examples/rtk-2-features.md) - **RTK 2.0**: combineSlices, inline selectors, buildCreateSlice - [middleware.md](examples/middleware.md) - Custom middleware - [testing.md](examples/testing.md) - Testing patterns - [integrations.md](examples/integrations.md) - Redux Persist - For decision frameworks and anti-patterns, see [reference.md](reference.md) --- ## CRITICAL: Before Managing State with Redux Toolkit **(You MUST use `configureStore` for store setup - NEVER legacy `createStore`)** **(You MUST use `createSlice` for all reducers - NEVER switch statements or manual action creators)** **(You MUST define typed hooks (`useAppSelector`, `useAppDispatch`) once in a hooks file)** **(You MUST use named exports ONLY - NO default exports in any Redux files)** **(You MUST use named constants for ALL numbers - NO magic numbers in state code)** --- **Auto-detection:** Redux Toolkit, createSlice, configureStore, RTK Query, createAsyncThunk, createEntityAdapter, useSelector, useDispatch **When to use:** - Complex client state requiring middleware, DevTools, or time-travel debugging - Enterprise applications with multiple teams needing predictable state management - Normalized entity state (lists of items with relationships) - Data fetching with sophisticated caching (RTK Query) - Applications requiring strict unidirectional data flow **Key patterns covered:** - Store configuration with `configureStore` - Slice creation with `createSlice` and Immer integration - **RTK 2.0**: Inline selectors in `createSlice`, `combineSlices`, `buildCreateSlice` for async thunks - RTK Query for data fetching and caching - Typed hooks for TypeScript integration - Entity adapters for normalized state - Async thunks with `createAsyncThunk` - Middleware patterns **When NOT to use:** - Simple UI state (useState or a lightweight state management solution) - Server state only (use a dedicated data fetching solution) - Small to medium apps where Redux overhead is unnecessary - Projects where team unfamiliarity with Redux outweighs benefits --- ## Philosophy Redux Toolkit (RTK) is the official, opinionated, batteries-included toolset for efficient Redux development. It eliminates the boilerplate of legacy Redux while maintaining predictable state management through strict unidirectional data flow. **Core principle:** "One source of truth" - All application state lives in a single store, changes are made through pure reducer functions, and state is never mutated directly. RTK uses Immer internally, allowing you to write "mutative" code that is actually immutable. This dramatically simplifies reducer logic while maintaining Redux's guarantees. **Key architecture decisions:** 1. **configureStore** replaces createStore with sensible defaults (DevTools, thunk middleware, development checks) 2. **createSlice** generates action creators and action types automatically from reducer names 3. **RTK Query** provides a purpose-built data fetching and caching solution 4. **createEntityAdapter** standardizes normalized state patterns --- ## Core Patterns ### Pattern 1: Store Configuration Use `configureStore` with proper TypeScript types inferred from the store itself. For store setup, typed hooks, and middleware configuration examples, see [examples/core.md](examples/core.md). --- ### Pattern 2: Slice Creation with createSlice Use `createSlice` to define reducers, actions, and initial state together. Immer allows "mutative" syntax for immutable updates. #### When to Use - All Redux state management - Generating action creators automatically - Simplifying immutable update logic #### When NOT to Use - State that belongs in URL params (filters, search) - Truly local component state (useState) - Server state that should use RTK Query or a data fetching solution For slice creation with typed state and PayloadAction, see [examples/core.md](examples/core.md). --- ### Pattern 3: Typed Hooks for Components Define typed versions of `useDispatch` and `useSelector` once, then use everywhere. This ensures type safety without repetitive type annotations. #### Why Typed Hooks Matter - `useSelector` saves typing `(state: RootState)` every time - `useDispatch` default type does not know about thunks - `AppDispatch` includes thunk middleware types for correct dispatch typing For typed hooks setup with `.withTypes()` (React Redux v9.1.0+), see [examples/typed-hooks.md](examples/typed-hooks.md). --- ### Pattern 4: RTK Query for Data Fetching RTK Query is a purpose-built data fetching and caching solution. Use it when you need caching, automatic refetching, and cache invalidation. #### When to Use RTK Query - Data fetching with caching requirements - Automatic refetch on focus/reconnect - Cache invalidation with tags - Optimistic updates for mutations #### When NOT to Use - Simple client state (use createSlice) - When an existing data fetching solution is already established in the codebase - When you need features RTK Query does not support For createApi setup, endpoint definitions, and cache tags, see [examples/rtk-query.md](examples/rtk-query.md). --- ### Pattern 5: Entity Adapters for Normalized State Use `createEntityAdapter` for collections of items (users, products, posts). It provides standardized CRUD operations and memoized selectors. #### When to Use - Lists of items with IDs - Relational data that needs normalization - CRUD operations on collections - Performance-critical large lists For entity adapter setup, CRUD operations, and selector usage, see [examples/entity-adapters.md](examples/entity-adapters.md). --- ### Pattern 6: Async Thunks with createAsyncThunk Use `createAsyncThunk` for async operations that need to dispatch multiple actions (pending, fulfilled, rejected). #### When to Use - Complex async flows not suited for RTK Query - Operations that need access to state during async flow - Chained async operations - Legacy code migration #### When NOT to Use - Standard API calls (prefer RTK Query) - Simple sync state updates (use createSlice actions) For async thunk creation and handling lifecycle actions, see [examples/async-thunks.md](examples/async-thunks.md). --- ### Pattern 7: Selectors and Memoization Create reusable selectors for derived state. Use `createSelector` from Reselect for memoized computed values. For selector patterns and memoization, see [examples/selectors.md](examples/selectors.md). --- ### Pattern 8: Middleware Patterns Add custom middleware for logging, analytics, or side effects. Use the middleware callback to extend default middleware. For middleware configuration and custom middleware, see [examples/middleware.md](examples/middleware.md). --- ## RED FLAGS **High Priority Issues:** - Using legacy `createStore` instead of `configureStore` -- misses DevTools, development checks, and middleware defaults - Switch statements in reducers -- use `createSlice` which generates action creators automatically - Manual action type strings -- `createSlice` generates these from reducer names - Mutating state outside Immer context -- only "mutate" inside `createSlice`/`createReducer` - Not adding RTK Query middleware to store -- caching, polling, and invalidation silently fail - RTK Query cache not blacklisted in redux-persist -- causes stale cache restoration on rehydration - RTK 2.0: Object syntax in `extraReducers` -- removed in v2, use builder callback - RTK 2.0: `AnyAction` type deprecated -- use `UnknownAction` with `isAction()` guard **Medium Priority Issues:** - Using untyped `useDispatch`/`useSelector` instead of typed hooks -- loses type safety for thunks and state - Defining typed hooks in the store file -- causes circular imports; put in separate `hooks.ts` - Storing derived state in the store -- compute in selectors instead - Not calling `setupListeners` for RTK Query -- refetchOnFocus/refetchOnReconnect will not work - Not using `rejectWithValue` in thunks -- loses typed error handling - Not using `createSelector` for derived data -- causes unnecessary recalculations on every render **Gotchas & Edge Cases:** - Immer mutations only work inside `createSlice`/`createReducer` -- not in action creators or thunks - Entity adapter `updateOne`/`updateMany` perform shallow merge -- deep nested updates need manual handling - RTK Query cache tags are case-sensitive -- `"User"` !== `"user"` - `createAsyncThunk` auto-dispatches pending/fulfilled/rejected -- do not dispatch these manually - `getDefaultMiddleware()` must be called (not referenced) in middleware config - TypeScript infers `RootState` from `store.getState` return type -- keep slice state types accurate See [reference.md](reference.md) for decision frameworks, anti-patterns with code examples, migration guides, and performance considerations. --- ## CRITICAL REMINDERS **(You MUST use `configureStore` for store setup - NEVER legacy `createStore`)** **(You MUST use `createSlice` for all reducers - NEVER switch statements or manual action creators)** **(You MUST define typed hooks (`useAppSelector`, `useAppDispatch`) once in a hooks file)** **(You MUST use named exports ONLY - NO default exports in any Redux files)** **(You MUST use named constants for ALL numbers - NO magic numbers in state code)** **Failure to follow these rules will cause type safety issues, unnecessary boilerplate, and convention violations.**