Performance Optimization Interview Questions

React.memo() is a higher-order component that memoizes component renders based on prop changes. Use it to prevent unnecessary re-renders of functional components when props haven't changed. Best for computationally expensive components.

useMemo memoizes computed values while useCallback memoizes functions. useMemo is used for expensive calculations, while useCallback is used for preventing recreation of function references that might trigger child re-renders.

Code splitting breaks the bundle into smaller chunks loaded on demand. Implement using React.lazy() and Suspense for component-based splitting, or using dynamic import() for route-based splitting.

Use virtualization (react-window or react-virtualized) to render only visible items. Implement windowing, pagination, or infinite scroll. Consider key optimization and memoization for list items.

Use code splitting, tree shaking, dynamic imports, and proper webpack configuration. Remove unused dependencies, implement proper chunking, and analyze bundle with tools like webpack-bundle-analyzer.

Use React.memo for functional components, PureComponent for class components, implement shouldComponentUpdate correctly, and properly structure component hierarchy to minimize prop changes.

Keys help React identify which items have changed, been added, or removed in lists. Proper key usage optimizes reconciliation process and prevents unnecessary DOM operations. Use stable, unique identifiers.

Implement lazy loading, use proper image formats and sizes, implement responsive images, use image CDNs, and consider modern formats like WebP. Implement proper caching strategies.

Context updates can cause all consuming components to re-render. Optimize by splitting context, using memoization, and implementing proper value comparison. Consider alternative state management for frequent updates.

Use Intersection Observer API, implement progressive loading, use lazy loading libraries, or create custom lazy loading components. Handle loading states and fallbacks appropriately.

Inline functions create new function references on every render, potentially causing unnecessary re-renders in child components. Use useCallback or class methods for event handlers in performance-critical scenarios.

Implement route-based code splitting, use proper caching strategies, optimize route matching, and implement proper loading states. Consider preloading routes and route-level data fetching.

Tree shaking eliminates unused code from the final bundle. Configure proper module imports, use ES modules, and ensure proper webpack configuration. Results in smaller bundle sizes and faster load times.

Use controlled components judiciously, implement debouncing for frequent updates, optimize validation timing, and consider uncontrolled components for simple forms. Handle large form state efficiently.

Choose appropriate state management solution, normalize state structure, implement proper selectors, and avoid unnecessary state updates. Consider using immutable data structures.

Minimize DOM mutations, use proper keys for lists, implement batch updates, and avoid direct DOM manipulation. Consider using React.Fragment to reduce DOM nodes.

Web Workers handle CPU-intensive tasks off the main thread. Implement for heavy computations, data processing, and background tasks. Consider using worker-loader or similar tools.

Implement proper caching, use debouncing/throttling, implement request cancellation, and optimize data fetching patterns. Consider using libraries like React Query or SWR.

Use CSS transforms and opacity, implement requestAnimationFrame, avoid layout thrashing, and consider using Web Animations API. Optimize animation frame rate and smooth transitions.

Use functional updates for state depending on previous value, batch updates when possible, and implement proper immutability patterns. Consider using immer or similar libraries.

Keys enable efficient list updates by helping React identify changed items. Use stable, unique identifiers as keys, avoid index as keys for dynamic lists, and ensure proper key propagation.

Analyze library size, implement proper tree shaking, consider alternatives, and load libraries on demand. Use bundle analyzer to identify large dependencies.

Implement CSS-in-JS optimizations, use CSS modules, remove unused styles, and implement proper code splitting for styles. Consider using modern CSS features and optimizing critical CSS.

Use React DevTools Profiler, implement performance metrics collection, monitor key user interactions, and track core web vitals. Consider using performance monitoring tools and analytics.

ErrorBoundaries prevent entire app crashes but can impact performance if overused. Implement strategically, handle errors appropriately, and consider performance implications of error tracking.

Implement proper data fetching strategies, optimize component rendering, implement caching, and handle hydration efficiently. Consider streaming SSR and selective hydration.

Use event delegation, implement proper cleanup, optimize handler reference stability, and consider debouncing/throttling. Handle memory leaks and event listener management.

Choose appropriate data structures, implement proper normalization, use immutable data patterns, and optimize state shape. Consider performance implications of deep nesting.

Use React DevTools effectively for performance profiling, identify unnecessary renders, analyze component updates, and track performance metrics. Implement proper debugging strategies.