zustand-state

What this skill does

# Zustand State Management

Minimal state management - no providers, minimal boilerplate.

## Quick Reference

```typescript
import { create } from 'zustand'

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

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

// In component - select only what you need
const bears = useBearStore((state) => state.bears)
const increase = useBearStore((state) => state.increase)
```

## State Updates

```typescript
// Flat updates (auto-merged at one level)
set({ bears: 5 })
set((state) => ({ bears: state.bears + 1 }))

// Nested objects (manual spread required)
set((state) => ({
  nested: { ...state.nested, count: state.nested.count + 1 }
}))

// Replace entire state (no merge)
set({ bears: 0 }, true)
```

## Selectors & Performance

```typescript
// Good - subscribes only to bears
const bears = useBearStore((state) => state.bears)

// Bad - rerenders on any change
const state = useBearStore()

// Multiple values with useShallow (prevents rerenders with shallow comparison)
import { useShallow } from 'zustand/react/shallow'

const { bears, fish } = useBearStore(
  useShallow((state) => ({ bears: state.bears, fish: state.fish }))
)

// Array destructuring also works
const [bears, fish] = useBearStore(
  useShallow((state) => [state.bears, state.fish])
)
```

## Access Outside Components

```typescript
// Get current state (non-reactive)
const state = useBearStore.getState()

// Update state
useBearStore.setState({ bears: 5 })

// Subscribe to changes
const unsub = useBearStore.subscribe((state) => console.log(state))
unsub() // unsubscribe
```

## Vanilla Store (No React)

```typescript
import { createStore } from 'zustand/vanilla'

const store = createStore((set) => ({
  bears: 0,
  increase: (by) => set((state) => ({ bears: state.bears + by })),
}))

store.getState().bears
store.setState({ bears: 10 })
store.subscribe((state) => console.log(state))
```

## Additional Documentation

- **Middleware**: See [references/middleware.md](references/middleware.md) for persist, devtools, immer
- **Patterns**: See [references/patterns.md](references/patterns.md) for slices, testing, best practices
- **TypeScript**: See [references/typescript.md](references/typescript.md) for advanced typing patterns

## Key Patterns

| Pattern | When to Use |
|---------|-------------|
| Single selector | One piece of state needed |
| `useShallow` | Multiple values, avoid rerenders |
| `getState()` | Outside React, event handlers |
| `subscribe()` | External systems, logging |
| Vanilla store | Non-React environments |

## Gates (persist and devtools)

Before merging code that uses these middlewares (see [references/middleware.md](references/middleware.md) for setup):

1. **`persist`** — **Pass when** persisted keys are explicit (`partialize` or a reviewed full-state snapshot) and the JSON written to storage cannot include auth tokens, API keys, or other secrets.
2. **`devtools` in shipped bundles** — **Pass when** DevTools runs only in development (env gate), or you leave a one-line note in the PR explaining why it stays enabled in production.