Zustand

Guidance for using Zustand (create, stores, middleware, and scaling patterns). No provider required.

Cursor rule

A file-scoped rule is provided at rules/zustand-stores.mdc. Copy it to your project’s .cursor/rules/ to get automatic reminders when editing store files.

When to Apply

• Adding or refactoring Zustand stores
• Persisting state (e.g. localStorage)
• Splitting a large store into slices
• User asks about Zustand, global state, or store structure

Store Basics

import { create } from 'zustand'

const useStore = create((set) => ({
  count: 0,
  inc: () => set((s) => ({ count: s.count + 1 })),
  reset: () => set({ count: 0 }),
}))

• set(state | fn): Replace state or use updater set((s) => ({ ... })).
• get(): Read current state inside actions (e.g. get().count).
• Prefer updater form for derived updates: set((s) => ({ count: s.count + 1 })).

Selectors and Re-renders

Select only what the component needs to avoid unnecessary re-renders.

// Bad – re-renders on any store change
const state = useStore()

// Good – re-renders only when count changes
const count = useStore((s) => s.count)
const inc = useStore((s) => s.inc)

Use shallow when selecting multiple fields:

import { useShallow } from 'zustand/react/shallow'

const { count, inc } = useStore(useShallow((s) => ({ count: s.count, inc: s.inc })))

Middleware

Persist (e.g. localStorage)

import { create } from 'zustand'
import { persist, createJSONStorage } from 'zustand/middleware'

const useStore = create(
  persist(
    (set) => ({
      token: null,
      setToken: (t) => set({ token: t }),
    }),
    {
      name: 'app-storage',
      storage: createJSONStorage(() => localStorage),
      partialize: (s) => ({ token: s.token }), // optional: persist only part
    },
  ),
)

For async storage (e.g. React Native), use a storage adapter that returns Promises; the store will rehydrate when the promise resolves.

Devtools

import { devtools } from 'zustand/middleware'

const useStore = create(
  devtools(
    (set) => ({ ... }),
    { name: 'MyStore' },
  ),
)

Combining Middleware

Order: store creator innermost, then devtools, then persist (so persist wraps the devtools-wrapped store).

create(
  persist(
    devtools((set) => ({ ... }), { name: 'AppStore' }),
    { name: 'app-storage' },
  ),
)

Slices Pattern (Scaling)

Split one store into slice creators; compose them in a single create call.

const createAuthSlice = (set) => ({
  user: null,
  login: (user) => set({ user }),
  logout: () => set({ user: null }),
})

const createUiSlice = (set) => ({
  theme: 'light',
  setTheme: (theme) => set({ theme }),
})

const useStore = create((...a) => ({
  ...createAuthSlice(...a),
  ...createUiSlice(...a),
}))

Each slice receives (set, get, store) and returns a plain object; avoid naming collisions between slices.

Immer (Mutable-style Updates)

Use immer middleware when updaters are complex or nested.

import { immer } from 'zustand/middleware/immer'

const useStore = create(
  immer((set) => ({
    nested: { a: 1, b: { c: 2 } },
    updateC: (v) => set((s) => {
      s.nested.b.c = v
    }),
  })),
)

TypeScript

Type the store state and actions; infer hook types from create.

interface BearState {
  bears: number
  addBear: () => void
}

const useBearStore = create<BearState>()((set) => ({
  bears: 0,
  addBear: () => set((s) => ({ bears: s.bears + 1 })),
}))

Use create<State>()(...) so middlewares keep correct typing.

Vanilla (Outside React)

Same store can be used without React: useStore.getState(), useStore.setState(...), useStore.subscribe((state) => { ... }).

Anti-patterns

• Don’t put everything in one giant store; prefer slices or multiple stores by domain.
• Don’t select the whole store in components; use selectors or useShallow for multiple fields.
• Don’t forget partialize with persist when the store has non-serializable values (e.g. functions, class instances).

Summary

Need	Use
Basic store	create((set) => ({ ... }))
Persist	persist(..., { name, storage })
DevTools	devtools(...)
Nested updates	immer
Scale store	Slice functions + spread in create
Fewer re-renders	Selectors or useShallow