React State Management

React State Management

Comprehensive guide to modern React state management patterns, from local component state to global stores and server state synchronization.

Do not use this skill when

• The task is unrelated to react state management
• You need a different domain or tool outside this scope

Instructions

• Clarify goals, constraints, and required inputs.
• Apply relevant best practices and validate outcomes.
• Provide actionable steps and verification.
• If detailed examples are required, open resources/implementation-playbook.md.

Use this skill when

• Setting up global state management in a React app
• Choosing between Redux Toolkit, Zustand, or Jotai
• Managing server state with React Query or SWR
• Implementing optimistic updates
• Debugging state-related issues
• Migrating from legacy Redux to modern patterns

Core Concepts

1. State Categories

2. Selection Criteria

Small app, simple state → Zustand or Jotai
Large app, complex state → Redux Toolkit
Heavy server interaction → React Query + light client state
Atomic/granular updates → Jotai

Quick Start

Zustand (Simplest)

// store/useStore.ts
import { create } from 'zustand'
import { devtools, persist } from 'zustand/middleware'

interface AppState {
  user: User | null
  theme: 'light' | 'dark'
  setUser: (user: User | null) => void
  toggleTheme: () => void
}

export const useStore = create<AppState>()(
  devtools(
    persist(
      (set) => ({
        user: null,
        theme: 'light',
        setUser: (user) => set({ user }),
        toggleTheme: () => set((state) => ({
          theme: state.theme === 'light' ? 'dark' : 'light'
        })),
      }),
      { name: 'app-storage' }
    )
  )
)

// Usage in component
function Header() {
  const { user, theme, toggleTheme } = useStore()
  return (
    <header className={theme}>
      {user?.name}
      <button onClick={toggleTheme}>Toggle Theme</button>
    </header>
  )
}

Patterns

Pattern 1: Redux Toolkit with 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

// 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)

// 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

// atoms/userAtoms.ts
import { atom } from 'jotai'
import { atomWithStorage } from 'jotai/utils'

// Basic atom
export const userAtom = atom<User | null>(null)

// Derived atom (computed)
export const isAuthenticatedAtom = atom((get) => get(userAtom) !== null)

// Atom with localStorage persistence
export const themeAtom = atomWithStorage<'light' | 'dark'>('theme', 'light')

// Async atom
export const userProfileAtom = atom(async (get) => {
  const user = get(userAtom)
  if (!user) return null
  const response = await fetch(`/api/users/${user.id}/profile`)
  return response.json()
})

// Write-only atom (action)
export const logoutAtom = atom(null, (get, set) => {
  set(userAtom, null)
  set(cartAtom, [])
  localStorage.removeItem('token')
})

// Usage
function Profile() {
  const [user] = useAtom(userAtom)
  const [, logout] = useAtom(logoutAtom)
  const [profile] = useAtom(userProfileAtom) // Suspense-enabled

  return (
    <Suspense fallback={<Skeleton />}>
      <ProfileContent profile={profile} onLogout={logout} />
    </Suspense>
  )
}

Pattern 4: React Query for Server State

// hooks/useUsers.ts
import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'

// Query keys factory
export const userKeys = {
  all: ['users'] as const,
  lists: () => [...userKeys.all, 'list'] as const,
  list: (filters: UserFilters) => [...userKeys.lists(), filters] as const,
  details: () => [...userKeys.all, 'detail'] as const,
  detail: (id: string) => [...userKeys.details(), id] as const,
}

// Fetch hook
export function useUsers(filters: UserFilters) {
  return useQuery({
    queryKey: userKeys.list(filters),
    queryFn: () => fetchUsers(filters),
    staleTime: 5 * 60 * 1000, // 5 minutes