react-state

Covers separating stores by domain (auth, cart, ui, theme) rather than one giant store, SOLID file organization (store.ts, store.interface.ts, use-store.ts), and forbidden patterns (persisting auth tokens, v4 syntax, skipping useShallow). This is the plain-React variant of Zustand (no App Router request-isolation concerns) — for Next.js App Router see nextjs-zustand, and for server state use TanStack Query instead of this skill.

Zustand for React

Minimal, scalable state management with React 18+ useSyncExternalStore.

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one Agent call each with a name:

1. fuse-ai-pilot:explore-codebase - Analyze existing stores and state patterns
2. fuse-ai-pilot:research-expert - Verify latest Zustand v5 docs via Context7/Exa
3. mcp__context7__query-docs - Check middleware and TypeScript patterns

After implementation, run fuse-ai-pilot:sniper for validation.

---

Overview

When to Use

• Managing global state in React applications
• Need state shared across components
• Persisting state to localStorage/sessionStorage
• Building UI state (modals, sidebars, theme, cart)
• Replacing React Context for complex state

Why Zustand v5

Feature	Benefit
Minimal API	Simple create() function, no boilerplate
React 18 native	useSyncExternalStore, no shims needed
TypeScript first	Full inference with currying pattern
Middleware stack	devtools, persist, immer composable
Bundle size	~2KB gzipped, smallest state library
No providers	Direct store access, no Context wrapper

---

Critical Rules

1. useShallow for arrays/objects - Prevent unnecessary re-renders
2. Currying syntax v5 - create<State>()((set) => ({...}))
3. SOLID paths - Stores in modules/[feature]/src/stores/
4. Separate stores - One store per domain (auth, cart, ui, theme)
5. Server state elsewhere - Use TanStack Query for server state

---

SOLID Architecture

Module Structure

Stores organized by feature module:

• modules/cores/stores/ - Shared stores (theme, ui)
• modules/auth/src/stores/ - Auth state
• modules/cart/src/stores/ - Cart state
• modules/[feature]/src/interfaces/ - Store types

File Organization

File	Purpose	Max Lines
store.ts	Store creation with create()	50
store.interface.ts	TypeScript interfaces	30
use-store.ts	Custom hook with selector	20

---

Key Concepts

Store Creation (v5 Syntax)

Double parentheses required for TypeScript inference. Currying pattern ensures full type safety.

Middleware Composition

Stack middlewares: devtools -> persist -> immer. Order matters for TypeScript types.

Selector Pattern

Always use useStore((s) => s.field) for performance. Use useShallow for array/object selectors.

---

Reference Guide

Need	Reference
Initial setup	installation.md
Store patterns	store-patterns.md
Middleware	middleware.md
TypeScript	typescript.md
Slices pattern	slices.md
Auto selectors	auto-selectors.md
Reset state	reset-state.md
Subscribe API	subscribe-api.md
Testing	testing.md
Migration v4→v5	migration-v5.md

---

Best Practices

1. Selector pattern - Always use useStore((s) => s.field) for performance
2. useShallow - Wrap array/object selectors to prevent re-renders
3. Separate stores - One store per domain (auth, cart, ui, theme)
4. Server data elsewhere - Use TanStack Query for server state
5. DevTools in dev only - Wrap devtools in process.env check
6. Partialize persist - Only persist necessary fields, never tokens

---

Forbidden Patterns

Pattern	Reason	Alternative
Persisting auth tokens	Security vulnerability	httpOnly cookies
Without useShallow on objects	Excessive re-renders	useShallow(selector)
v4 syntax	TypeScript inference broken	v5 currying create<T>()()
Giant monolithic store	Hard to maintain	Slices or separate stores