react-patterns - Agent Skills

React Patterns

> Principles for building production-ready React applications.

1. Component Design Principles

Component Types

Type	Use	State
Server	Data fetching, static	None
Client	Interactivity	useState, effects
Presentational	UI display	Props only
Container	Logic/state	Heavy state

Design Rules

One responsibility per component

Props down, events up

Composition over inheritance

Prefer small, focused components

2. Hook Patterns

When to Extract Hooks

Pattern	Extract When
useLocalStorage	Same storage logic needed
useDebounce	Multiple debounced values
useFetch	Repeated fetch patterns
useForm	Complex form state

Hook Rules

Hooks at top level only

Same order every render

Custom hooks start with "use"

Clean up effects on unmount

3. State Management Selection

Complexity	Solution
Simple	useState, useReducer
Shared local	Context
Server state	React Query, SWR
Complex global	Zustand, Redux Toolkit

State Placement

Scope	Where
Single component	useState
Parent-child	Lift state up
Subtree	Context
App-wide	Global store

4. React 19 Patterns

New Hooks

Hook	Purpose
useActionState	Form submission state
useOptimistic	Optimistic UI updates
use	Read resources in render

Compiler Benefits

Automatic memoization

Less manual useMemo/useCallback

Focus on pure components

5. Composition Patterns

Compound Components

Parent provides context

Children consume context

Flexible slot-based composition

Example: Tabs, Accordion, Dropdown

Render Props vs Hooks

Use Case	Prefer
Reusable logic	Custom hook
Render flexibility	Render props
Cross-cutting	Higher-order component

6. Performance Principles

When to Optimize

Signal	Action
Slow renders	Profile first
Large lists	Virtualize
Expensive calc	useMemo
Stable callbacks	useCallback

Optimization Order

Check if actually slow

Profile with DevTools

Identify bottleneck

Apply targeted fix

7. Error Handling

Error Boundary Usage

Scope	Placement
App-wide	Root level
Feature	Route/feature level
Component	Around risky component

Error Recovery

Show fallback UI

Log error

Offer retry option

Preserve user data

8. TypeScript Patterns

Props Typing

Pattern	Use
Interface	Component props
Type	Unions, complex
Generic	Reusable components

Common Types

Need	Type
Children	ReactNode
Event handler	MouseEventHandler
Ref	RefObject<Element>

9. Testing Principles

Level	Focus
Unit	Pure functions, hooks
Integration	Component behavior
E2E	User flows

Test Priorities

User-visible behavior

Edge cases

Error states

Accessibility

10. Anti-Patterns

❌ Don't	✅ Do
Prop drilling deep	Use context
Giant components	Split smaller
useEffect for everything	Server components
Premature optimization	Profile first
Index as key	Stable unique ID

> Remember: React is about composition. Build small, combine thoughtfully.