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name: react-patterns description: Modern React patterns and principles. Hooks, composition, performance, TypeScript best practices. allowed-tools: Read, Write, Edit, Glob, Grep

React Patterns

Principles for building production-ready React applications.

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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

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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

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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

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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

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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

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6. Performance Principles

When to Optimize

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

Optimization Order

1. Check if actually slow
2. Profile with DevTools
3. Identify bottleneck
4. Apply targeted fix

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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

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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>

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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

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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

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