React State Management

# react-state-management — detailed patterns and worked examples

## Patterns

### Pattern 1: Redux Toolkit with TypeScript

```typescript
// store/index.ts
import { configureStore } from "@reduxjs/toolkit";
import { TypedUseSelectorHook, useDispatch, useSelector } from "react-redux";
import userReducer from "./slices/userSlice";
import cartReducer from "./slices/cartSlice";

export const store = configureStore({
  reducer: {
    user: userReducer,
    cart: cartReducer,
  },
  middleware: (getDefaultMiddleware) =>
    getDefaultMiddleware({
      serializableCheck: {
        ignoredActions: ["persist/PERSIST"],
      },
    }),
});

export type RootState = ReturnType<typeof store.getState>;
export type AppDispatch = typeof store.dispatch;

// Typed hooks
export const useAppDispatch: () => AppDispatch = useDispatch;
export const useAppSelector: TypedUseSelectorHook<RootState> = useSelector;
```

```typescript
// store/slices/userSlice.ts
import { createSlice, createAsyncThunk, PayloadAction } from "@reduxjs/toolkit";

interface User {
  id: string;
  email: string;
  name: string;
}

interface UserState {
  current: User | null;
  status: "idle" | "loading" | "succeeded" | "failed";
  error: string | null;
}

const initialState: UserState = {
  current: null,
  status: "idle",
  error: null,
};

export const fetchUser = createAsyncThunk(
  "user/fetchUser",
  async (userId: string, { rejectWithValue }) => {
    try {
      const response = await fetch(`/api/users/${userId}`);
      if (!response.ok) throw new Error("Failed to fetch user");
      return await response.json();
    } catch (error) {
      return rejectWithValue((error as Error).message);
    }
  },
);

const userSlice = createSlice({
  name: "user",
  initialState,
  reducers: {
    setUser: (state, action: PayloadAction<User>) => {
      state.current = action.payload;
      state.status = "succeeded";
    },
    clearUser: (state) => {
      state.current = null;
      state.status = "idle";
    },
  },
  extraReducers: (builder) => {
    builder
      .addCase(fetchUser.pending, (state) => {
        state.status = "loading";
        state.error = null;
      })
      .addCase(fetchUser.fulfilled, (state, action) => {
        state.status = "succeeded";
        state.current = action.payload;
      })
      .addCase(fetchUser.rejected, (state, action) => {
        state.status = "failed";
        state.error = action.payload as string;
      });
  },
});

export const { setUser, clearUser } = userSlice.actions;
export default userSlice.reducer;
```

### Pattern 2: Zustand with Slices (Scalable)

```typescript
// store/slices/createUserSlice.ts
import { StateCreator } from "zustand";

export interface UserSlice {
  user: User | null;
  isAuthenticated: boolean;
  login: (credentials: Credentials) => Promise<void>;
  logout: () => void;
}

export const createUserSlice: StateCreator<
  UserSlice & CartSlice, // Combined store type
  [],
  [],
  UserSlice
> = (set, get) => ({
  user: null,
  isAuthenticated: false,
  login: async (credentials) => {
    const user = await authApi.login(credentials);
    set({ user, isAuthenticated: true });
  },
  logout: () => {
    set({ user: null, isAuthenticated: false });
    // Can access other slices
    // get().clearCart()
  },
});

// store/index.ts
import { create } from "zustand";
import { createUserSlice, UserSlice } from "./slices/createUserSlice";
import { createCartSlice, CartSlice } from "./slices/createCartSlice";

type StoreState = UserSlice & CartSlice;

export const useStore = create<StoreState>()((...args) => ({
  ...createUserSlice(...args),
  ...createCartSlice(...args),
}));

// Selective subscriptions (prevents unnecessary re-renders)
export const useUser = () => useStore((state) => state.user);
export const useCart = () => useStore((state) => state.cart);
```

### Pattern 3: Jotai for Atomic State

```typescript
// atoms/userAtoms.ts
import { atom } from 'jotai'
import { atomWithStorage } from 'jotai/util