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name: reviewing-performance-patterns description: Review React 19 performance patterns including memoization, re-renders, and bundle size. Use when reviewing performance or optimization. review: true allowed-tools: Read, Grep version: 1.0.0

Review: Performance Patterns

Checklist

Re-Rendering

• No unnecessary re-renders from prop changes
• Using React Compiler when possible (reduces manual memoization)
• Context split for different concerns (avoid re-render cascades)
• Children prop pattern to prevent wrapper re-renders

Memoization

• Manual useMemo/useCallback only when needed (React Compiler handles most cases)
• React.memo used selectively for expensive components
• Dependencies correct in memoization hooks
• Not over-optimizing (premature optimization)

Bundle Size

• Code splitting used for heavy components/routes
• Server Components used where appropriate (zero client JS)
• 'use client' only where needed
• Lazy loading for non-critical components

Resource Loading

• Using preload/preinit for critical resources
• DNS prefetch for external domains
• Images optimized and lazy loaded
• Fonts preloaded

Anti-Patterns

• ❌ Array index as key (causes unnecessary re-renders)
• ❌ Creating new objects/arrays in render (breaks memoization)
• ❌ Excessive memoization without measurement
• ❌ Unnecessary 'use client' (increases bundle)

For comprehensive performance patterns, see: research/react-19-comprehensive.md.