Basic Store

import { create } from "zustand";

interface CounterStore { count: number; increment: () => void; decrement: () => void; reset: () => void; }

const useCounterStore = create<CounterStore>((set) => ({ count: 0, increment: () => set((state) => ({ count: state.count + 1 })), decrement: () => set((state) => ({ count: state.count - 1 })), reset: () => set({ count: 0 }), }));

// Usage function Counter() { const { count, increment, decrement } = useCounterStore(); return ( <div> <span>{count}</span> <button onClick={increment}>+</button> <button onClick={decrement}>-</button> </div> ); }

Persist Middleware

import { create } from "zustand"; import { persist } from "zustand/middleware";

interface SettingsStore { theme: "light" | "dark"; language: string; setTheme: (theme: "light" | "dark") => void; setLanguage: (language: string) => void; }

const useSettingsStore = create<SettingsStore>()( persist( (set) => ({ theme: "light", language: "en", setTheme: (theme) => set({ theme }), setLanguage: (language) => set({ language }), }), { name: "settings-storage", // localStorage key } ) );

Selectors (Zustand 5)

// ✅ Select specific fields to prevent unnecessary re-renders function UserName() { const name = useUserStore((state) => state.name); return <span>{name}</span>; }

// ✅ For multiple fields, use useShallow import { useShallow } from "zustand/react/shallow";

function UserInfo() { const { name, email } = useUserStore( useShallow((state) => ({ name: state.name, email: state.email })) ); return <div>{name} - {email}</div>; }

// ❌ AVOID: Selecting entire store (causes re-render on any change) const store = useUserStore(); // Re-renders on ANY state change

Async Actions

interface UserStore { user: User | null; loading: boolean; error: string | null; fetchUser: (id: string) => Promise<void>; }

const useUserStore = create<UserStore>((set) => ({ user: null, loading: false, error: null,

fetchUser: async (id) => { set({ loading: true, error: null }); try { const response = await fetch(/api/users/${id}); const user = await response.json(); set({ user, loading: false }); } catch (error) { set({ error: "Failed to fetch user", loading: false }); } }, }));

Slices Pattern

// userSlice.ts interface UserSlice { user: User | null; setUser: (user: User) => void; clearUser: () => void; }

const createUserSlice = (set): UserSlice => ({ user: null, setUser: (user) => set({ user }), clearUser: () => set({ user: null }), });

// cartSlice.ts interface CartSlice { items: CartItem[]; addItem: (item: CartItem) => void; removeItem: (id: string) => void; }

const createCartSlice = (set): CartSlice => ({ items: [], addItem: (item) => set((state) => ({ items: [...state.items, item] })), removeItem: (id) => set((state) => ({ items: state.items.filter(i => i.id !== id) })), });

// store.ts type Store = UserSlice & CartSlice;

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

Immer Middleware

import { create } from "zustand"; import { immer } from "zustand/middleware/immer";

interface TodoStore { todos: Todo[]; addTodo: (text: string) => void; toggleTodo: (id: string) => void; }

const useTodoStore = create<TodoStore>()( immer((set) => ({ todos: [],

addTodo: (text) => set((state) => {
  // Mutate directly with Immer!
  state.todos.push({ id: crypto.randomUUID(), text, done: false });
}),

toggleTodo: (id) => set((state) => {
  const todo = state.todos.find(t => t.id === id);
  if (todo) todo.done = !todo.done;
}),

})) );

DevTools

import { create } from "zustand"; import { devtools } from "zustand/middleware";

const useStore = create<Store>()( devtools( (set) => ({ // store definition }), { name: "MyStore" } // Name in Redux DevTools ) );

Outside React

// Access store outside components const { count, increment } = useCounterStore.getState(); increment();

// Subscribe to changes const unsubscribe = useCounterStore.subscribe( (state) => console.log("Count changed:", state.count) );