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React Performance

Expert

React.memo, useMemo, useCallback, virtualization, code splitting, Profiler, Web Vitals & bundle optimization

The Golden Rule of React Optimization

Don't optimize prematurely. Measure first with React DevTools Profiler and browser performance tools. Most apps are fast enough without optimization. The three main categories: reduce renders (memo/useCallback), reduce work per render (useMemo), and reduce bundle size (code splitting).

React.memo — Skip Re-renders of Unchanged Components

intermediate

memo() wraps a component so it only re-renders if its props change. Pair with useCallback to stabilize function props.

useMemo — Memoize Expensive Calculations

intermediate

Cache the result of an expensive computation between renders. Only recompute when dependencies change. Don't overuse — the comparison itself has a cost.

useTransition & useDeferredValue — Concurrent Mode

advanced

Mark state updates as non-urgent so React can interrupt them to handle urgent updates (typing, clicking). Keeps UI responsive during heavy re-renders.

Code Splitting — lazy() & Suspense

intermediate

Dynamically import components to split your bundle. React.lazy() + Suspense enables route-level and component-level splitting with zero boilerplate.

Virtualization — Render Only Visible Items

advanced

For large lists (1,000+ items), only render what's visible in the viewport. Use TanStack Virtual (formerly react-virtual) for best-in-class virtualization.

React Profiler & Web Vitals

expert

Use React DevTools Profiler to identify slow renders. Monitor Core Web Vitals (LCP, FID, CLS) to measure real-world performance.

⚡ Performance Resources

📚React Performance Docs 📝Kent C. Dodds — useMemo & useCallback 📚TanStack Virtual Docs 📝Web.dev Core Web Vitals 📚Next.js Performance Docs 📚React DevTools (Chrome Extension)▶️StackBlitz — Performance Playground