Zustand State Management

Last Updated: 2026-01-21 Latest Version: [email protected] (released 2026-01-12) Dependencies: React 18-19, TypeScript 5+

Quick Start

npm install zustand

TypeScript Store (CRITICAL: use create<T>()() double parentheses):

import { create } from 'zustand'

interface BearStore {
  bears: number
  increase: (by: number) => void
}

const useBearStore = create<BearStore>()((set) => ({
  bears: 0,
  increase: (by) => set((state) => ({ bears: state.bears + by })),
}))

Use in Components:

const bears = useBearStore((state) => state.bears)  // Only re-renders when bears changes
const increase = useBearStore((state) => state.increase)

Core Patterns

Basic Store (JavaScript):

const useStore = create((set) => ({
  count: 0,
  increment: () => set((state) => ({ count: state.count + 1 })),
}))

TypeScript Store (Recommended):

interface CounterStore { count: number; increment: () => void }
const useStore = create<CounterStore>()((set) => ({
  count: 0,
  increment: () => set((state) => ({ count: state.count + 1 })),
}))

Persistent Store (survives page reloads):

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

const useStore = create<UserPreferences>()(
  persist(
    (set) => ({ theme: 'system', setTheme: (theme) => set({ theme }) }),
    { name: 'user-preferences', storage: createJSONStorage(() => localStorage) },
  ),
)

Critical Rules

Always Do

✅ Use create<T>()() (double parentheses) in TypeScript for middleware compatibility ✅ Define separate interfaces for state and actions ✅ Use selector functions to extract specific state slices ✅ Use set with updater functions for derived state: set((state) => ({ count: state.count + 1 })) ✅ Use unique names for persist middleware storage keys ✅ Handle Next.js hydration with hasHydrated flag pattern ✅ Use useShallow hook for selecting multiple values ✅ Keep actions pure (no side effects except state updates)

Never Do

❌ Use create<T>(...) (single parentheses) in TypeScript - breaks middleware types ❌ Mutate state directly: set((state) => { state.count++; return state }) - use immutable updates ❌ Create new objects in selectors: useStore((state) => ({ a: state.a })) - causes infinite renders ❌ Use same storage name for multiple stores - causes data collisions ❌ Access localStorage during SSR without hydration check ❌ Use Zustand for server state - use TanStack Query instead ❌ Export store instance directly - always export the hook

Known Issues Prevention

This skill prevents 6 documented issues:

Issue #1: Next.js Hydration Mismatch

Error: "Text content does not match server-rendered HTML" or "Hydration failed"

Source:

• DEV Community: Persist middleware in Next.js
• GitHub Discussions #2839

Why It Happens: Persist middleware reads from localStorage on client but not on server, causing state mismatch.

Prevention:

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

interface StoreWithHydration {
  count: number
  _hasHydrated: boolean
  setHasHydrated: (hydrated: boolean) => void
  increase: () => void
}

const useStore = create<StoreWithHydration>()(
  persist(
    (set) => ({
      count: 0,
      _hasHydrated: false,
      setHasHydrated: (hydrated) => set({ _hasHydrated: hydrated }),
      increase: () => set((state) => ({ count: state.count + 1 })),
    }),
    {
      name: 'my-store',
      onRehydrateStorage: () => (state) => {
        state?.setHasHydrated(true)
      },
    },
  ),
)

// In component
function MyComponent() {
  const hasHydrated = useStore((state) => state._hasHydrated)

  if (!hasHydrated) {
    return <div>Loading...</div>
  }

  // Now safe to render with persisted state
  return <ActualContent />
}

Issue #2: TypeScript Double Parentheses Missing

Error: Type inference fails, StateCreator types break with middleware

Source: Official Zustand TypeScript Guide

Why It Happens: The currying syntax create<T>()() is required for middleware to work with TypeScript inference.

Prevention:

// ❌ WRONG - Single parentheses
const useStore = create<MyStore>((set) => ({
  // ...
}))

// ✅ CORRECT - Double parentheses
const useStore = create<MyStore>()((set) 
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