React Performance
Overview
Dedicated performance optimization skill for React applications. Covers the full spectrum from build-time optimizations (code splitting, barrel file avoidance) through runtime techniques (memoization, transitions, content-visibility) to diagnostic tooling (React DevTools Profiler, bundle analyzers).
When to use: Reducing Time to Interactive, shrinking bundle size, eliminating re-renders, profiling slow components, optimizing large lists, lazy loading heavy dependencies, auditing React app performance.
When NOT to use: General React component patterns (use react-patterns skill), framework-specific optimizations like Next.js caching (use framework skill), non-React performance (network, database, CDN).
Quick Reference
| Category | Technique | Key Points |
|---|---|---|
| Compiler | React Compiler | Automatic memoization at build time; eliminates manual memo/useMemo/useCallback |
| Memoization | React.memo(Component) | Wrap components receiving stable primitive props from frequently re-rendering parents |
| Memoization | useMemo(fn, deps) | Expensive computations only: sorting, filtering, Set/Map construction |
| Memoization | useCallback(fn, deps) | Only when passed to memoized children; use functional setState for stable refs |
| Splitting | React.lazy(() => import()) | Lazy-load heavy components with <Suspense> fallback |
| Splitting | Preload on intent | Trigger import() on hover/focus for perceived speed |
| Bundle | Direct imports | Avoid barrel files; import from specific paths to reduce module count |
| Bundle | Defer third-party | Load analytics, logging after hydration |
| Re-renders | startTransition | Mark non-urgent updates (search, scroll tracking) as interruptible |
| Re-renders | Functional setState | setState(prev =>...) eliminates state dependencies from callbacks |
| Re-renders | Derived state | Subscribe to booleans, not continuous values; compute during render |
| Re-renders | Defer state reads | Read dynamic state (searchParams) inside callbacks, not at render |
| Rendering | content-visibility: auto | Skip layout/paint for off-screen items in long lists |
| Rendering | Hoist static JSX | Extract constant elements outside component functions |
| Profiling | React DevTools Profiler | Record renders, identify slow components, flamegraph analysis |
| Profiling | Bundle analyzer | Visualize chunk sizes, find oversized dependencies |
Common Mistakes
| Mistake | Correct Pattern |
|---|---|
| Wrapping everything in useMemo/useCallback | Trust React Compiler first; only memoize expensive computations or memoized-child callbacks |
Memoizing cheap operations like value * 2 | Skip memo for simple primitives; overhead exceeds recomputation cost |
Importing from barrel files (lucide-react, @mui/material) | Import directly from specific paths or use optimizePackageImports |
| Loading analytics/tracking in the initial bundle | Defer with lazy + mounted state to load after hydration |
| Subscribing to continuous values (window width) for boolean checks | Use useMediaQuery or derived boolean to re-render only on threshold change |
| Referencing state in useCallback dependency array | Use functional setState setState(prev =>...) for stable callbacks |
Using useEffect to derive state from props | Compute derived values during render; effects add an extra render cycle |
| Creating new object literals as props on every render | Hoist static objects outside component; use useMemo for dynamic objects |
| Profiling in development mode | Always profile production builds; dev mode includes extra warnings that skew results |
Delegation
- Profile and diagnose performance bottlenecks: Use
Exploreagent to run React DevTools Profiler, analyze bundle composition, and trace re-render cascades - Apply performance optimizations to existing code: Use
Taskagent to implement code splitting, add memoization boundaries, and optimize rendering - Plan performance improvement strategy: Use
Planagent to prioritize optimizations by impact (waterfalls > bundle > re-renders) and create an optimization roadmap
If thereact-patternsskill is available, delegate general component architecture and React 19 API questions to it. Otherwise, recommend:npx skills add oakoss/agent-skills --skill react-patterns