SKILL.md
$27
// Usage
function Counter() {
const { count, increment, decrement } = useCounterStore();
return (
{count}
+
-
);
}
## Persist Middleware
import { create } from "zustand";
import { persist } from "zustand/middleware";
interface SettingsStore {
theme: "light" | "dark";
language: string;
setTheme: (theme: "light" | "dark") => void;
setLanguage: (language: string) => void;
}
const useSettingsStore = create<SettingsStore>()(
persist(
(set) => ({
theme: "light",
language: "en",
setTheme: (theme) => set({ theme }),
setLanguage: (language) => set({ language }),
}),
{
name: "settings-storage", // localStorage key
}
)
);
## Selectors (Zustand 5)
// ✅ Select specific fields to prevent unnecessary re-renders
function UserName() {
const name = useUserStore((state) => state.name);
return <span>{name}</span>;
}
// ✅ For multiple fields, use useShallow
import { useShallow } from "zustand/react/shallow";
function UserInfo() {
const { name, email } = useUserStore(
useShallow((state) => ({ name: state.name, email: state.email }))
);
return <div>{name} - {email}</div>;
}
// ❌ AVOID: Selecting entire store (causes re-render on any change)
const store = useUserStore(); // Re-renders on ANY state change
## Async Actions
interface UserStore {
user: User | null;
loading: boolean;
error: string | null;
fetchUser: (id: string) => Promise<void>;
}
const useUserStore = create<UserStore>((set) => ({
user: null,
loading: false,
error: null,
fetchUser: async (id) => {
set({ loading: true, error: null });
try {
const response = await fetch(/api/users/${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)
);