ReactJS Interview Questions Your Guide to Success

ReactJS is a leading library for building dynamic and responsive user interfaces, making it an essential skill for frontend and full-stack developers. Stark.ai offers curated ReactJS interview questions, hands-on challenges, and expert insights to help you stand out in your next interview.

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  • advanced

    • What are custom hooks in React?

      Custom hooks in React are functions that allow you to reuse stateful logic across components. They start with the...

  • JSX and Components

    • What are Pure Components and when should they be used?

      Pure Components (React.PureComponent or React.memo) implement shouldComponentUpdate with a shallow prop and state...

    • What are Higher-Order Components (HOCs) and what problems do they solve?

      HOCs are functions that take a component and return a new component with additional props or behavior. They're used...

    • How do you optimize component rendering using memo?

      React.memo is a higher-order component that prevents unnecessary re-renders by memoizing the result. It performs a...

    • What are portals in React and when would you use them?

      Portals (ReactDOM.createPortal) allow rendering children into a DOM node outside the parent component's hierarchy....

    • How do you handle dynamic imports for components?

      Dynamic imports use React.lazy() with Suspense component for code splitting. This allows components to be loaded...

    • What are error boundaries and how do they work?

      Error boundaries are components that catch JavaScript errors in child component tree, log errors, and display...

    • How do you handle component communication beyond props?

      Beyond props, components can communicate through context API, event emitters, state management libraries...

    • What are the considerations for component reusability?

      Reusable components should be generic, well-documented, properly typed, have clear props API, handle edge cases,...

  • State Management

    • How does React batch state updates and why is it important?

      React batches multiple state updates in the same synchronous event handler for performance. This means multiple...

    • What are the common pitfalls of useState and how to avoid them?

      Common pitfalls include: mutating state directly, not using functional updates for state depending on previous...

    • What is the useEffect cleanup function's role in state management?

      Cleanup functions in useEffect prevent memory leaks and stale state updates by canceling subscriptions or pending...

    • How do you optimize Context API to prevent unnecessary re-renders?

      Split context into smaller, focused contexts, use React.memo for consumer components, implement value memoization...

    • How do you implement state persistence in React applications?

      State persistence can be achieved using localStorage/sessionStorage with useEffect, custom hooks for storage...

    • What are the benefits of using state machines for complex state?

      State machines provide predictable state transitions, clear visualization of possible states, prevent impossible...

    • What are derived states and when should they be used?

      Derived state is calculated from existing state/props during render. Use useMemo for expensive calculations. Avoid...

    • How do you implement undo/redo functionality with state?

      Implement undo/redo using an array of past states and current index. Use useReducer for complex state history...

    • How do you handle state synchronization between components?

      State synchronization can be achieved through lifting state up, using Context API, implementing pub/sub patterns...

    • How do you handle state updates in nested objects?

      Use immutable update patterns with spread operator or libraries like immer. Create new object references at each...

    • What are the best practices for state organization in large applications?

      Organize state by feature/domain, keep state as close as needed to components, use appropriate mix of local and...

    • What are the considerations for state management in server-side rendering?

      Handle initial state hydration, avoid state mismatches between server and client, implement proper state...

    • How do you implement optimistic updates in state management?

      Update UI immediately before API confirmation, maintain temporary and permanent state, implement proper rollback...

    • How do you handle real-time state updates with WebSockets?

      Implement WebSocket connections in useEffect, handle connection lifecycle, update state with incoming messages, and...

    • What are the strategies for state caching and memoization?

      Use useMemo for expensive computations, implement proper cache invalidation strategies, leverage browser storage for...

  • Component Lifecycle

    • What is the difference between useEffect and useLayoutEffect?

      useEffect runs asynchronously after render completion, while useLayoutEffect runs synchronously before browser...

    • What is the purpose of getDerivedStateFromProps and how can it be handled with Hooks?

      getDerivedStateFromProps updates state based on prop changes. With hooks, use useEffect to observe prop changes and...

    • How do you optimize component updates using lifecycle methods or hooks?

      In class components, use shouldComponentUpdate or extend PureComponent. In functional components, use React.memo for...

    • What are the common pitfalls in useEffect dependencies?

      Common pitfalls include: missing dependencies leading to stale closures, infinite loops from mutable values,...

    • How do lifecycle methods and hooks handle async operations?

      Both can initiate async operations but require different patterns. Class methods need mounted flags for safety,...

    • What are the implications of the strict mode on component lifecycle?

      Strict mode double-invokes certain lifecycle methods and hooks to help identify side effects. This includes...

    • How do you handle DOM measurements in the component lifecycle?

      Use componentDidMount or useLayoutEffect for DOM measurements to ensure the DOM is ready. Store measurements in...

    • What is the impact of Suspense on component lifecycle?

      Suspense can interrupt component mounting and trigger fallback rendering. Effects may be delayed or re-run. Consider...

    • What are the considerations for state updates during different lifecycle phases?

      Avoid state updates in render phase. Use componentDidMount/Update or effects for async state updates. Consider...

    • How do you manage resource preloading in the component lifecycle?

      Implement preloading in componentDidMount or useEffect with empty dependency array. Consider using Suspense for data...

    • What are the best practices for handling websocket connections in lifecycle methods?

      Establish connections in componentDidMount or useEffect, handle reconnection logic in componentDidUpdate or with...

    • How do you handle component persistence throughout lifecycle changes?

      Implement storage updates in effects or lifecycle methods, handle rehydration on mount, and clean up on unmount....

    • What are the patterns for managing multiple effects in a component?

      Split effects by concern, manage dependencies independently, consider effect ordering, and implement proper cleanup...

  • React Hooks

    • What is the purpose of the useImperativeHandle hook?

      useImperativeHandle customizes the instance value exposed to parent components when using ref. It allows you to...

    • How do you optimize performance with useMemo and useCallback?

      Use useMemo for expensive calculations and useCallback for function props passed to optimized child components....

    • What is the useLayoutEffect hook and when should it be used instead of useEffect?

      useLayoutEffect fires synchronously after DOM mutations but before browser paint. Use it when you need to make DOM...

    • What are the patterns for sharing stateful logic between components using hooks?

      Create custom hooks that encapsulate the shared logic, state, and side effects. Ensure hooks are generic enough for...

    • What is the useDebugValue hook and when should it be used?

      useDebugValue adds a label to custom hooks in React DevTools. Use it to display custom hook values for debugging....

    • What are the common pitfalls when using the dependency array in hooks?

      Common pitfalls include: missing dependencies leading to stale closures, unnecessary dependencies causing excess...

    • What is the pattern for implementing debouncing with hooks?

      Use useCallback and useRef to create a debounced function that delays execution. Clear previous timeout in cleanup....

    • How do you handle error boundaries with hooks?

      Since error boundaries must be class components, create a custom hook that works with an error boundary component....

    • What is the pattern for implementing undo/redo functionality with hooks?

      Use useReducer to manage state history array and current index. Implement actions for undo, redo, and new states....

    • What are the patterns for managing WebSocket connections with hooks?

      Create a custom hook that establishes connection in useEffect, handles message events, and cleans up on unmount....

    • What are the patterns for implementing authentication with hooks?

      Create custom hooks for managing auth state, token storage, and user session. Handle login, logout, token refresh,...

    • How do you implement infinite scroll with hooks?

      Create a custom hook that manages scroll position, loading state, and data fetching. Use intersection observer or...

    • What are the patterns for implementing keyboard shortcuts with hooks?

      Create a custom hook that manages keyboard event listeners using useEffect. Handle key combinations, prevent default...

    • How do you implement state machine patterns with hooks?

      Use useReducer with a state machine configuration. Define states, transitions, and actions. Consider using libraries...

  • Props and Data Flow

    • What are render props and how do they enable component reuse?

      Render props are functions passed as props that return React elements. They enable sharing behavior between...

    • How do you implement prop validation for complex data structures?

      Use PropTypes.shape() for objects, PropTypes.arrayOf() for arrays, and custom validators for complex validation....

    • What are Higher-Order Components (HOCs) and how do they handle props?

      HOCs are functions that take a component and return an enhanced component. They can manipulate props, add new props,...

    • How do you optimize component re-renders based on prop changes?

      Use React.memo for functional components or PureComponent for class components to prevent unnecessary re-renders....

    • How do you handle prop types in TypeScript with React?

      Define interfaces or types for props: interface Props { name: string; age?: number; }. Use them in component...

    • How do you handle async data flow with props?

      Pass loading states and error states as props along with data. Use promises or async/await in parent components....

    • What are compound components and how do they use props?

      Compound components are related components that work together sharing implicit state. They often use Context...

    • How do you handle prop updates in animations and transitions?

      Use useEffect to watch for prop changes and trigger animations. Consider using libraries like Framer Motion. Handle...

    • How do you handle derived state from props?

      Prefer computing values during render instead of storing in state. Use useMemo for expensive calculations. If state...

    • How do you handle prop validation errors in production?

      Remove PropTypes in production builds for performance. Implement error boundaries for runtime errors. Consider...

    • How do you handle circular prop dependencies?

      Avoid circular prop passing. Restructure component hierarchy. Consider using Context or state management. Break...

    • How do you implement prop-based code splitting?

      Use dynamic imports based on props. Implement proper loading states. Handle errors during chunk loading. Consider...

    • What are the patterns for handling sensitive data in props?

      Never expose sensitive data in client-side props. Use proper authentication and authorization. Consider encryption...

  • Event Handling

    • What are the best practices for handling async operations in event handlers?

      Use async/await or promises, handle loading and error states, prevent memory leaks with cleanup, consider...

    • What are custom events in React and how do you create them?

      Custom events can be created using new CustomEvent() and dispatched using dispatchEvent(). In React, prefer prop...

    • What are the patterns for handling drag and drop events?

      Use HTML5 drag and drop events (onDragStart, onDrop, etc.). Implement dataTransfer for data passing. Consider using...

    • What are the considerations for handling mobile touch events?

      Handle touchstart, touchmove, touchend events. Consider touch gestures, preventing scroll during touch interactions,...

    • How do you implement debouncing and throttling for event handlers?

      Use custom hooks or utility functions for debounce/throttle. Consider cleanup on unmount. Example: const...

    • What are the patterns for handling nested event handlers?

      Use event.stopPropagation() to prevent bubbling, organize handlers hierarchically, consider event delegation, and...

    • What are the considerations for handling WebSocket events?

      Set up WebSocket connections in useEffect, handle connection events, implement proper cleanup, and manage message...

    • How do you implement custom event hooks?

      Create hooks that encapsulate event logic, handle setup/cleanup, manage event state, and provide simple interfaces....

    • What are the patterns for handling scroll events efficiently?

      Use throttling or requestAnimationFrame for scroll handlers, consider intersection observer for scroll detection,...

    • How do you implement event handling for animations?

      Handle animation start/end events, manage animation state, implement cleanup for interrupted animations, and...

    • What are the patterns for handling media events?

      Handle play, pause, loadeddata, error events for audio/video elements. Implement proper cleanup, manage playback...

    • How do you handle events in portals?

      Events bubble up through React's virtual DOM hierarchy regardless of portal placement. Consider event propagation,...

    • What are the considerations for handling events in SSR?

      Handle hydration mismatches, avoid accessing window/document during SSR, implement proper event attachment after...

    • How do you implement event pooling optimization?

      React 17+ removed event pooling, but understanding includes: using event.persist() for async access in older...

    • What are the patterns for handling intersection observer events?

      Create custom hooks for intersection observer, handle observer setup/cleanup, manage intersection state, and...

  • Forms and Controlled Components

    • How do you handle file inputs in React forms?

      File inputs are typically uncontrolled. Access files through e.target.files in onChange handler. Use FileReader for...

    • What are the considerations for handling form state updates performance?

      Consider debouncing for frequent updates, batch state updates when possible, use memoization for expensive...

    • How do you implement custom form controls as controlled components?

      Create components that accept value and onChange props, maintain internal state if needed, properly handle user...

    • What are the patterns for handling nested form data?

      Use nested objects in state, implement proper update logic for nested fields, consider using libraries for complex...

    • How do you handle form wizard or multi-step forms in React?

      Maintain overall form state across steps, validate each step independently, handle navigation between steps, persist...

    • How do you implement form data persistence and recovery?

      Use localStorage/sessionStorage to save form state, implement auto-save functionality, handle form recovery on page...

    • What are the patterns for handling dynamic form fields?

      Maintain array of fields in state, implement add/remove field functionality, handle validation for dynamic fields....

    • What are the patterns for handling async form validation?

      Implement debounced validation calls, handle loading states, cache validation results when appropriate. Consider...

    • How do you handle form submission with file uploads?

      Use FormData for file uploads, handle upload progress, implement proper error handling and retry logic. Consider...

    • How do you handle form internationalization?

      Implement proper label and error message translations, handle different date/number formats, consider right-to-left...

    • What are the patterns for implementing form autosave functionality?

      Implement debounced save function, handle save states and errors, provide user feedback. Consider conflict...

    • How do you handle form state management with Context or Redux?

      Implement proper actions and reducers for form state, handle form namespacing, consider performance implications....

    • What are the considerations for handling form performance with large datasets?

      Implement virtualization for large lists, optimize validation runs, use proper memoization. Consider chunking large...

    • How do you implement custom select or autocomplete components?

      Handle controlled component behavior, implement proper keyboard navigation, manage dropdown state and positioning....

    • What are the patterns for handling form submission retry logic?

      Implement exponential backoff, handle different error types, maintain submission state. Consider user feedback...

    • What are the best practices for handling form security?

      Implement CSRF protection, validate inputs server-side, handle sensitive data properly, prevent XSS attacks....

    • What are the patterns for handling form optimization in SSR?

      Handle initial form state hydration, prevent flash of uncontrolled inputs, implement proper client-side validation...

  • React Router

    • What is route-based code splitting and how is it implemented?

      Use React.lazy and Suspense with React Router to load components dynamically. Implement per-route code splitting for...

    • How do you implement route transitions?

      Use React Transition Group with React Router. Implement enter/exit animations, handle route-based transitions, and...

    • What is server-side rendering with React Router?

      Use StaticRouter instead of BrowserRouter for SSR. Handle location context, match routes on server, and manage data...

    • How do you implement breadcrumbs?

      Use route configuration and current location to generate breadcrumbs. Handle dynamic segments, maintain breadcrumb...

    • How do you handle route guards?

      Implement higher-order components or custom Route components for protection. Handle authentication, authorization,...

    • How do you handle scroll restoration?

      Implement custom scroll behavior using useEffect. Handle scroll position per route, manage scroll restoration, and...

    • How do you handle route-based code splitting with prefetching?

      Implement React.lazy with prefetching strategies. Handle component preloading, manage loading states, and optimize...

    • What is memory router?

      MemoryRouter keeps history in memory (not in URL). Useful for testing and non-browser environments. Maintains...

    • How do you test routing logic?

      Use MemoryRouter for testing, mock route matches and history. Test navigation, protected routes, and route...

  • Performance Optimization

    • How do you optimize large lists in React?

      Use virtualization (react-window or react-virtualized) to render only visible items. Implement windowing,...

    • What is the impact of context on performance?

      Context updates can cause all consuming components to re-render. Optimize by splitting context, using memoization,...

    • How do you optimize React Router performance?

      Implement route-based code splitting, use proper caching strategies, optimize route matching, and implement proper...

    • How do you optimize form performance in React?

      Use controlled components judiciously, implement debouncing for frequent updates, optimize validation timing, and...

    • What are the best practices for state management performance?

      Choose appropriate state management solution, normalize state structure, implement proper selectors, and avoid...

    • What is the role of Web Workers in React performance?

      Web Workers handle CPU-intensive tasks off the main thread. Implement for heavy computations, data processing, and...

    • What are the performance considerations for animations?

      Use CSS transforms and opacity, implement requestAnimationFrame, avoid layout thrashing, and consider using Web...

    • How do you implement performance monitoring?

      Use React DevTools Profiler, implement performance metrics collection, monitor key user interactions, and track core...

    • What is the impact of ErrorBoundary on performance?

      ErrorBoundaries prevent entire app crashes but can impact performance if overused. Implement strategically, handle...

    • How do you optimize server-side rendering performance?

      Implement proper data fetching strategies, optimize component rendering, implement caching, and handle hydration...

    • How do you implement efficient data structures in React?

      Choose appropriate data structures, implement proper normalization, use immutable data patterns, and optimize state...

  • Context API

    • What are the performance implications of using Context?

      Context triggers re-renders in all consuming components when its value changes. Optimize by splitting contexts,...

    • How do you optimize context with memo?

      Use React.memo on consuming components, memoize context value with useMemo, implement proper value comparison....

    • What are context selectors and how do you implement them?

      Context selectors help consume specific parts of context to prevent unnecessary re-renders. Implement using custom...

    • What are the patterns for combining Context with Reducers?

      Use useReducer with Context for complex state management, implement proper action dispatching, handle state updates...

    • How do you handle async operations with Context?

      Combine Context with useEffect for async operations, handle loading and error states, implement proper state...

    • What is context composition and when should you use it?

      Compose multiple contexts to separate concerns, improve maintainability, and optimize performance. Use when...

    • What are the common pitfalls when using Context?

      Overusing context, unnecessary re-renders, improper value memoization, context hell (too many nested providers)....

    • What are the patterns for handling form state with Context?

      Use context for form state management, implement proper validation, handle field updates efficiently. Consider form...

    • How do you handle context in TypeScript?

      Define proper types for context values, use generic types when needed, implement type checking. Consider type safety...

    • How do you handle context persistence?

      Implement storage synchronization, handle hydration, manage persistence lifecycle. Consider storage options and...

    • How do you handle context cleanup and disposal?

      Implement proper cleanup in effects, handle unmount scenarios, manage resource disposal. Consider memory leaks and...

    • What are the patterns for handling dynamic contexts?

      Create contexts dynamically, handle context creation lifecycle, manage dynamic providers. Consider performance and...

  • Error Handling

    • How do you implement error recovery mechanisms?

      Implement retry logic, state reset mechanisms, fallback UI, and proper error clearing. Consider user experience and...

    • How do you handle errors in React hooks?

      Use try-catch in effects, implement error states, handle cleanup properly, consider custom hooks for error handling....

    • How do you handle errors in Redux/state management?

      Implement error reducers, handle async action errors, provide error states in store, consider middleware for error...

    • What are the best practices for error boundary placement?

      Place boundaries strategically to isolate failures, consider component hierarchy, implement granular error handling....

    • How do you handle errors in React Suspense?

      Use Error Boundaries with Suspense, handle loading errors, implement fallback UI, manage timeout scenarios. Consider...

    • What are the patterns for error handling in HOCs?

      Implement error handling logic in HOCs, wrap components with error boundaries, handle prop validation errors....

    • How do you handle errors in React portals?

      Use error boundaries around portals, handle portal-specific errors, manage cleanup on errors. Consider modal and...

    • How do you implement graceful degradation in error scenarios?

      Provide fallback functionality, implement feature detection, handle browser compatibility issues. Consider...

    • How do you handle errors in server-side rendering?

      Implement SSR-specific error handling, manage hydration errors, handle state reconciliation issues. Consider...

    • How do you handle memory leaks and cleanup errors?

      Implement proper cleanup in useEffect, handle component unmounting, manage resource disposal. Consider async...

    • What are the strategies for error monitoring in production?

      Implement error tracking services, collect error metrics, analyze error patterns, set up alerts. Consider privacy...

    • How do you implement error tracking and analytics?

      Integrate error tracking services, collect relevant error data, implement proper error categorization. Consider...

    • What are the best practices for testing error scenarios?

      Test error boundaries, simulate different error conditions, verify error recovery, implement comprehensive test...

  • Testing React Applications

    • How do you test custom hooks?

      Use @testing-library/react-hooks with renderHook, test different scenarios and state changes, verify hook behavior...

    • How do you test React components with Redux?

      Provide test store using Provider, mock store state and actions, test component integration with Redux. Consider...

    • How do you implement integration tests in React?

      Test component interactions, data flow between components, state management integration. Focus on user workflows and...

    • What are the strategies for testing error boundaries?

      Simulate errors to test boundary behavior, verify fallback UI rendering, test error recovery. Consider different...

    • What are the best practices for mocking in React tests?

      Mock external dependencies, API calls, and complex functionality. Use jest.mock() appropriately, maintain mock...

    • How do you test accessibility in React components?

      Use jest-axe for accessibility testing, verify ARIA attributes, test keyboard navigation. Consider screen reader...

    • What are the patterns for testing animations and transitions?

      Test animation triggers and completion, verify state changes during transitions, mock timers appropriately. Consider...

    • How do you test performance optimizations?

      Test render counts, verify memoization effectiveness, check optimization implementations. Consider performance...

    • What are the strategies for testing file uploads?

      Mock File API, test upload handlers, verify file validation and processing. Consider different file types and error...

    • How do you implement E2E testing in React?

      Use Cypress or Playwright for end-to-end testing, test complete user flows, verify application integration. Consider...

    • How do you test React portals?

      Test portal rendering and content, verify portal functionality and events. Consider DOM structure and cleanup.

    • How do you test React suspense and lazy loading?

      Test loading states, verify component lazy loading, check suspense fallbacks. Consider network conditions and timing.

    • What are the patterns for testing state management?

      Test state updates and transitions, verify state synchronization, check state persistence. Consider complex state...

    • How do you implement visual regression testing?

      Use tools like Percy or Chromatic, compare visual changes, maintain visual consistency. Consider different viewport...

  • Styling in React

    • What are the performance implications of different styling approaches?

      CSS-in-JS can impact runtime performance, CSS Modules have build-time overhead, inline styles prevent browser...

    • How do you implement CSS-in-JS with TypeScript?

      Use proper type definitions for styled components, implement theme typing, handle prop types for styled components....

    • How do you handle CSS specificity in React applications?

      Use CSS Modules for scoping, implement proper class naming conventions, manage specificity hierarchy. Consider...

    • How do you implement RTL support in React styling?

      Use CSS logical properties, implement directional styles, handle bidirectional text properly. Consider cultural...

    • How do you handle CSS transitions with React Router?

      Implement page transition animations, handle route-based styles, manage transition states. Consider performance and...

    • What are the patterns for implementing styled system props?

      Use style props for component customization, implement consistent prop interfaces, handle style composition....

    • How do you optimize CSS delivery in React applications?

      Implement critical CSS, handle code splitting, optimize load performance. Consider caching strategies and resource hints.

    • What are the approaches to handling CSS-in-JS server-side rendering?

      Handle style extraction, implement proper hydration, manage style injection. Consider performance and flash of...

    • How do you handle dynamic styling based on data?

      Implement data-driven styles, handle dynamic classes and properties, manage style updates. Consider performance and...

    • What are the patterns for implementing design tokens?

      Define and manage design tokens, implement token-based styling system, handle theme variations. Consider...

    • What are the approaches to testing styled components?

      Test style rendering, verify theme integration, check dynamic styles. Consider snapshot testing and visual...

  • React Best Practices

    • What are the performance optimization best practices in React?

      Use React.memo for expensive components, implement proper key usage, avoid unnecessary re-renders, use proper...

    • What are the recommended patterns for API integration?

      Implement proper data fetching patterns, handle loading and error states, implement caching strategies, maintain...

    • What are the best practices for accessibility?

      Follow ARIA guidelines, implement proper keyboard navigation, maintain proper heading hierarchy, provide proper alt...

    • What are the best practices for type safety?

      Use TypeScript or PropTypes, implement proper type definitions, maintain type consistency, handle type edge cases,...

    • What are the recommended patterns for context usage?

      Use context appropriately for global state, implement proper provider organization, optimize context updates, avoid...

    • What are the best practices for code reusability?

      Implement proper component composition, create reusable hooks, maintain proper abstraction levels, implement proper...

    • What are the best practices for security?

      Prevent XSS attacks, handle sensitive data properly, implement proper authentication/authorization, validate inputs,...

    • What are the recommended patterns for performance monitoring?

      Implement proper performance metrics, use React DevTools effectively, monitor render performance, track user...

    • What are the best practices for code splitting?

      Implement proper lazy loading, use dynamic imports effectively, handle loading states, optimize bundle size, and...

    • What are the best practices for internationalization?

      Implement proper i18n solution, handle translations effectively, manage locale changes, consider RTL support, and...

    • What are the recommended patterns for state persistence?

      Implement proper storage strategies, handle state rehydration, manage persistence lifecycle, consider offline...

    • What are the recommended patterns for progressive enhancement?

      Implement proper fallbacks, handle feature detection, maintain core functionality, consider browser support, and...

    • What are the best practices for deployment?

      Implement proper build process, optimize asset delivery, handle environment variables, implement proper CI/CD, and...

  • React and APIs

    • How do you handle authentication with APIs?

      Manage tokens securely, handle token refresh, implement interceptors for requests, manage auth state. Consider...

    • How do you implement request caching?

      Use caching libraries (React Query, SWR), implement local storage caching, handle cache invalidation, manage cache...

    • What are the patterns for handling real-time data?

      Implement WebSocket connections, handle Socket.IO integration, manage real-time state updates, handle connection...

    • What are the best practices for API request optimization?

      Implement request debouncing/throttling, batch requests when possible, optimize payload size, use proper caching...

    • What are the patterns for handling offline functionality?

      Implement service workers, handle offline storage, manage sync queues, handle conflict resolution. Consider...

    • How do you implement optimistic updates?

      Update UI immediately before API confirmation, handle rollback on failure, manage temporary state, implement proper...

    • What are the patterns for handling API rate limiting?

      Implement request queuing, handle rate limit errors, manage retry strategies, provide user feedback. Consider...

    • What are the best practices for API security?

      Implement proper authentication/authorization, handle CORS, prevent XSS attacks, manage sensitive data. Consider...

    • How do you implement API request queuing?

      Handle sequential requests, manage request priority, implement queue processing logic. Consider error handling and...

    • What are the best practices for API performance monitoring?

      Track request times, monitor error rates, implement performance metrics, analyze bottlenecks. Consider monitoring...

    • What are the patterns for handling GraphQL in React?

      Use Apollo Client or other GraphQL clients, manage queries and mutations, handle caching, implement proper error...

    • How do you handle API request batching?

      Implement request combining, manage batch processing, handle response correlation, optimize network usage. Consider...

    • What are the patterns for handling API state persistence?

      Implement local storage caching, handle state rehydration, manage persistence lifecycle. Consider storage strategies...

What are custom hooks in React?

Custom hooks in React are functions that allow you to reuse stateful logic across components. They start with the word `use` and can encapsulate complex logic using existing React hooks like `useState` and `useEffect`.

What are Pure Components and when should they be used?

Pure Components (React.PureComponent or React.memo) implement shouldComponentUpdate with a shallow prop and state comparison. They're used to optimize performance by preventing unnecessary re-renders when props or state haven't changed significantly.

What are Higher-Order Components (HOCs) and what problems do they solve?

HOCs are functions that take a component and return a new component with additional props or behavior. They're used for code reuse, adding additional functionality like data fetching, authentication, or logging. HOCs follow the pattern: const EnhancedComponent = higherOrderComponent(WrappedComponent).

How do you optimize component rendering using memo?

React.memo is a higher-order component that prevents unnecessary re-renders by memoizing the result. It performs a shallow comparison of props and only re-renders if props have changed. Useful for performance optimization in components with expensive renders.

What are portals in React and when would you use them?

Portals (ReactDOM.createPortal) allow rendering children into a DOM node outside the parent component's hierarchy. Useful for modals, tooltips, or floating elements that need to break out of parent container limitations while maintaining React context.

How do you handle dynamic imports for components?

Dynamic imports use React.lazy() with Suspense component for code splitting. This allows components to be loaded only when needed: const DynamicComponent = React.lazy(() => import('./Component')). Suspense provides fallback content during loading.

What are error boundaries and how do they work?

Error boundaries are components that catch JavaScript errors in child component tree, log errors, and display fallback UI. They must be class components using componentDidCatch or static getDerivedStateFromError. They don't catch errors in event handlers or async code.

How do you handle component communication beyond props?

Beyond props, components can communicate through context API, event emitters, state management libraries (Redux/MobX), or custom hooks. Choice depends on scope of communication, app size, and performance requirements.

What are the considerations for component reusability?

Reusable components should be generic, well-documented, properly typed, have clear props API, handle edge cases, maintain single responsibility, and be tested thoroughly. Consider composition, prop drilling, and state management needs.

How does React batch state updates and why is it important?

React batches multiple state updates in the same synchronous event handler for performance. This means multiple setState calls may be processed in a single re-render. In async operations, use functional updates (prevState => newState) to ensure correct state updates.

What are the common pitfalls of useState and how to avoid them?

Common pitfalls include: mutating state directly, not using functional updates for state depending on previous value, initializing with expensive operations without lazy initialization, and not considering batching behavior in async operations.

What is the useEffect cleanup function's role in state management?

Cleanup functions in useEffect prevent memory leaks and stale state updates by canceling subscriptions or pending operations when component unmounts or dependencies change. Return a cleanup function from useEffect for proper resource management.

How do you optimize Context API to prevent unnecessary re-renders?

Split context into smaller, focused contexts, use React.memo for consumer components, implement value memoization with useMemo, and consider using context selectors. Avoid putting frequently changing values in context.

How do you implement state persistence in React applications?

State persistence can be achieved using localStorage/sessionStorage with useEffect, custom hooks for storage synchronization, or state management libraries with persistence middleware. Consider serialization and hydration strategies.

What are the benefits of using state machines for complex state?

State machines provide predictable state transitions, clear visualization of possible states, prevent impossible states, and make complex workflows manageable. Libraries like XState help implement state machines in React.

What are derived states and when should they be used?

Derived state is calculated from existing state/props during render. Use useMemo for expensive calculations. Avoid storing derived values in state; compute them during render to prevent state synchronization issues.

How do you implement undo/redo functionality with state?

Implement undo/redo using an array of past states and current index. Use useReducer for complex state history management. Consider memory usage and performance implications for large state objects.

How do you handle state synchronization between components?

State synchronization can be achieved through lifting state up, using Context API, implementing pub/sub patterns with custom events, or using state management libraries. Consider performance and complexity trade-offs.

How do you handle state updates in nested objects?

Use immutable update patterns with spread operator or libraries like immer. Create new object references at each level of nesting. Consider flattening state structure when possible to simplify updates.

What are the best practices for state organization in large applications?

Organize state by feature/domain, keep state as close as needed to components, use appropriate mix of local and global state, implement proper state normalization, and document state shape and update patterns.

What are the considerations for state management in server-side rendering?

Handle initial state hydration, avoid state mismatches between server and client, implement proper state serialization, and consider using state management solutions that support SSR like Redux or Zustand.

How do you implement optimistic updates in state management?

Update UI immediately before API confirmation, maintain temporary and permanent state, implement proper rollback mechanisms for failures, and handle race conditions in concurrent updates.

How do you handle real-time state updates with WebSockets?

Implement WebSocket connections in useEffect, handle connection lifecycle, update state with incoming messages, and implement proper cleanup. Consider using libraries like Socket.io or custom hooks for WebSocket state.

What are the strategies for state caching and memoization?

Use useMemo for expensive computations, implement proper cache invalidation strategies, leverage browser storage for persistence, and consider using caching libraries like react-query for server state.

What is the difference between useEffect and useLayoutEffect?

useEffect runs asynchronously after render completion, while useLayoutEffect runs synchronously before browser paint. useLayoutEffect is used for DOM measurements and mutations that need to be synchronized with rendering to prevent visual flicker.

What is the purpose of getDerivedStateFromProps and how can it be handled with Hooks?

getDerivedStateFromProps updates state based on prop changes. With hooks, use useEffect to observe prop changes and update state accordingly, but consider if derived state is really needed versus computing values during render.

How do you optimize component updates using lifecycle methods or hooks?

In class components, use shouldComponentUpdate or extend PureComponent. In functional components, use React.memo for props comparison and useMemo/useCallback to prevent unnecessary re-renders of child components.

What are the common pitfalls in useEffect dependencies?

Common pitfalls include: missing dependencies leading to stale closures, infinite loops from mutable values, unnecessary re-renders from object/array dependencies, and over-dependency on external values. Use ESLint rules and proper dependency management.

How do lifecycle methods and hooks handle async operations?

Both can initiate async operations but require different patterns. Class methods need mounted flags for safety, while hooks can use cleanup functions to cancel pending operations. Consider race conditions and component unmounting.

What are the implications of the strict mode on component lifecycle?

Strict mode double-invokes certain lifecycle methods and hooks to help identify side effects. This includes constructor, render, and useEffect. Use it to catch lifecycle-related bugs and ensure proper cleanup implementation.

How do you handle DOM measurements in the component lifecycle?

Use componentDidMount or useLayoutEffect for DOM measurements to ensure the DOM is ready. Store measurements in state or refs. Consider resize observers and window event listeners with proper cleanup.

What is the impact of Suspense on component lifecycle?

Suspense can interrupt component mounting and trigger fallback rendering. Effects may be delayed or re-run. Consider the implications for data fetching, lazy loading, and error handling in lifecycle methods and effects.

What are the considerations for state updates during different lifecycle phases?

Avoid state updates in render phase. Use componentDidMount/Update or effects for async state updates. Consider batching updates and proper error handling. Be aware of setState's asynchronous nature.

How do you manage resource preloading in the component lifecycle?

Implement preloading in componentDidMount or useEffect with empty dependency array. Consider using Suspense for data fetching and lazy loading. Handle cleanup for abandoned preload requests.

What are the best practices for handling websocket connections in lifecycle methods?

Establish connections in componentDidMount or useEffect, handle reconnection logic in componentDidUpdate or with dependencies, and clean up in componentWillUnmount or effect cleanup. Consider connection state management.

How do you handle component persistence throughout lifecycle changes?

Implement storage updates in effects or lifecycle methods, handle rehydration on mount, and clean up on unmount. Consider using localStorage/sessionStorage with proper serialization and cleanup.

What are the patterns for managing multiple effects in a component?

Split effects by concern, manage dependencies independently, consider effect ordering, and implement proper cleanup for each effect. Use custom hooks to encapsulate related effect logic.

What is the purpose of the useImperativeHandle hook?

useImperativeHandle customizes the instance value exposed to parent components when using ref. It allows you to control which values and methods are accessible via the ref, enabling better encapsulation of component internals.

How do you optimize performance with useMemo and useCallback?

Use useMemo for expensive calculations and useCallback for function props passed to optimized child components. Ensure dependency arrays are properly configured. Only use when there's a measurable performance benefit to avoid unnecessary complexity.

What is the useLayoutEffect hook and when should it be used instead of useEffect?

useLayoutEffect fires synchronously after DOM mutations but before browser paint. Use it when you need to make DOM measurements or mutations that should be synchronized with rendering to prevent visual flickers.

What are the patterns for sharing stateful logic between components using hooks?

Create custom hooks that encapsulate the shared logic, state, and side effects. Ensure hooks are generic enough for reuse but specific enough to be useful. Consider composition of multiple hooks for complex logic.

What is the useDebugValue hook and when should it be used?

useDebugValue adds a label to custom hooks in React DevTools. Use it to display custom hook values for debugging. Consider using the format function parameter to defer expensive formatting until the hook is inspected.

What are the common pitfalls when using the dependency array in hooks?

Common pitfalls include: missing dependencies leading to stale closures, unnecessary dependencies causing excess renders, object/array dependencies causing infinite loops, and circular dependencies. Use ESLint rules and proper dependency management.

What is the pattern for implementing debouncing with hooks?

Use useCallback and useRef to create a debounced function that delays execution. Clear previous timeout in cleanup. Consider returning both debounced and immediate execution functions.

How do you handle error boundaries with hooks?

Since error boundaries must be class components, create a custom hook that works with an error boundary component. Use try-catch in event handlers and effects. Consider implementing retry logic and error logging.

What is the pattern for implementing undo/redo functionality with hooks?

Use useReducer to manage state history array and current index. Implement actions for undo, redo, and new states. Consider memory usage and limiting history size for large state objects.

What are the patterns for managing WebSocket connections with hooks?

Create a custom hook that establishes connection in useEffect, handles message events, and cleans up on unmount. Consider reconnection logic, message queuing, and connection status management.

What are the patterns for implementing authentication with hooks?

Create custom hooks for managing auth state, token storage, and user session. Handle login, logout, token refresh, and protected routes. Consider persistent sessions and security implications.

How do you implement infinite scroll with hooks?

Create a custom hook that manages scroll position, loading state, and data fetching. Use intersection observer or scroll events. Consider data caching, cleanup, and performance optimization.

What are the patterns for implementing keyboard shortcuts with hooks?

Create a custom hook that manages keyboard event listeners using useEffect. Handle key combinations, prevent default behaviors, and clean up listeners. Consider focus management and accessibility.

How do you implement state machine patterns with hooks?

Use useReducer with a state machine configuration. Define states, transitions, and actions. Consider using libraries like XState. Handle side effects and state persistence.

What are render props and how do they enable component reuse?

Render props are functions passed as props that return React elements. They enable sharing behavior between components: <DataProvider render={data => <Display data={data} />}. This pattern allows for flexible component composition.

How do you implement prop validation for complex data structures?

Use PropTypes.shape() for objects, PropTypes.arrayOf() for arrays, and custom validators for complex validation. Example: PropTypes.shape({ id: PropTypes.number, items: PropTypes.arrayOf(PropTypes.object) }).

What are Higher-Order Components (HOCs) and how do they handle props?

HOCs are functions that take a component and return an enhanced component. They can manipulate props, add new props, or handle prop-related logic. Important to properly forward props: {...props} to avoid prop isolation.

How do you optimize component re-renders based on prop changes?

Use React.memo for functional components or PureComponent for class components to prevent unnecessary re-renders. Implement shouldComponentUpdate for custom comparison. Consider prop structure and reference equality.

How do you handle prop types in TypeScript with React?

Define interfaces or types for props: interface Props { name: string; age?: number; }. Use them in component definitions: const Component: React.FC<Props> = ({name, age}) => {}. TypeScript provides compile-time type safety.

How do you handle async data flow with props?

Pass loading states and error states as props along with data. Use promises or async/await in parent components. Consider implementing loading skeletons or error boundaries. Handle race conditions in updates.

What are compound components and how do they use props?

Compound components are related components that work together sharing implicit state. They often use Context internally while exposing a declarative API through props. Example: <Select><Option value='1'>One</Option></Select>.

How do you handle prop updates in animations and transitions?

Use useEffect to watch for prop changes and trigger animations. Consider using libraries like Framer Motion. Handle cleanup of animation timeouts. Manage transition states properly.

How do you handle derived state from props?

Prefer computing values during render instead of storing in state. Use useMemo for expensive calculations. If state is needed, update it in useEffect. Consider getDerivedStateFromProps in class components.

How do you handle prop validation errors in production?

Remove PropTypes in production builds for performance. Implement error boundaries for runtime errors. Consider logging prop validation errors. Use TypeScript for compile-time validation.

How do you handle circular prop dependencies?

Avoid circular prop passing. Restructure component hierarchy. Consider using Context or state management. Break circular dependencies through component composition.

How do you implement prop-based code splitting?

Use dynamic imports based on props. Implement proper loading states. Handle errors during chunk loading. Consider performance implications and bundle size.

What are the patterns for handling sensitive data in props?

Never expose sensitive data in client-side props. Use proper authentication and authorization. Consider encryption for necessary client-side data. Implement proper cleanup.

What are the best practices for handling async operations in event handlers?

Use async/await or promises, handle loading and error states, prevent memory leaks with cleanup, consider debouncing/throttling, and handle component unmounting. Example: async handleClick() { try { await apiCall() } catch (error) { handleError() } }

What are custom events in React and how do you create them?

Custom events can be created using new CustomEvent() and dispatched using dispatchEvent(). In React, prefer prop callbacks or event emitters for component communication. Handle cleanup for custom event listeners.

What are the patterns for handling drag and drop events?

Use HTML5 drag and drop events (onDragStart, onDrop, etc.). Implement dataTransfer for data passing. Consider using react-dnd or similar libraries for complex cases. Handle drag preview and drop zones.

What are the considerations for handling mobile touch events?

Handle touchstart, touchmove, touchend events. Consider touch gestures, preventing scroll during touch interactions, and handling multi-touch. Test on various devices and implement fallbacks for desktop.

How do you implement debouncing and throttling for event handlers?

Use custom hooks or utility functions for debounce/throttle. Consider cleanup on unmount. Example: const debouncedHandler = useDebounce(handler, delay). Handle edge cases and cancellation.

What are the patterns for handling nested event handlers?

Use event.stopPropagation() to prevent bubbling, organize handlers hierarchically, consider event delegation, and handle event order carefully. Avoid deeply nested event handling logic.

What are the considerations for handling WebSocket events?

Set up WebSocket connections in useEffect, handle connection events, implement proper cleanup, and manage message events. Consider reconnection logic and error handling.

How do you implement custom event hooks?

Create hooks that encapsulate event logic, handle setup/cleanup, manage event state, and provide simple interfaces. Example: useEventListener hook for declarative event handling.

What are the patterns for handling scroll events efficiently?

Use throttling or requestAnimationFrame for scroll handlers, consider intersection observer for scroll detection, and implement cleanup properly. Handle scroll position restoration and virtual scrolling.

How do you implement event handling for animations?

Handle animation start/end events, manage animation state, implement cleanup for interrupted animations, and consider performance. Use requestAnimationFrame for smooth animations.

What are the patterns for handling media events?

Handle play, pause, loadeddata, error events for audio/video elements. Implement proper cleanup, manage playback state, and handle loading/buffering. Consider mobile device considerations.

How do you handle events in portals?

Events bubble up through React's virtual DOM hierarchy regardless of portal placement. Consider event propagation, handle cleanup properly, and manage portal lifecycle.

What are the considerations for handling events in SSR?

Handle hydration mismatches, avoid accessing window/document during SSR, implement proper event attachment after hydration, and consider initial state handling.

How do you implement event pooling optimization?

React 17+ removed event pooling, but understanding includes: using event.persist() for async access in older versions, handling synthetic event limitations, and managing event object lifecycle.

What are the patterns for handling intersection observer events?

Create custom hooks for intersection observer, handle observer setup/cleanup, manage intersection state, and implement proper threshold configuration. Use for infinite scroll or lazy loading.

How do you handle file inputs in React forms?

File inputs are typically uncontrolled. Access files through e.target.files in onChange handler. Use FileReader for preview, FormData for upload. Handle multiple files, validation, and upload progress. Consider drag-and-drop functionality.

What are the considerations for handling form state updates performance?

Consider debouncing for frequent updates, batch state updates when possible, use memoization for expensive validations, optimize re-renders with proper component structure. Balance real-time validation with performance.

How do you implement custom form controls as controlled components?

Create components that accept value and onChange props, maintain internal state if needed, properly handle user interactions, and implement proper event handling. Ensure compatibility with form libraries and validation.

What are the patterns for handling nested form data?

Use nested objects in state, implement proper update logic for nested fields, consider using libraries for complex state updates. Example: setState({...form, address: {...form.address, street: value}}). Handle array fields appropriately.

How do you handle form wizard or multi-step forms in React?

Maintain overall form state across steps, validate each step independently, handle navigation between steps, persist partial data. Consider using reducers for complex state management and proper error handling.

How do you implement form data persistence and recovery?

Use localStorage/sessionStorage to save form state, implement auto-save functionality, handle form recovery on page reload. Consider cleaning up saved data and handling version conflicts.

What are the patterns for handling dynamic form fields?

Maintain array of fields in state, implement add/remove field functionality, handle validation for dynamic fields. Consider performance implications and proper state updates for array manipulations.

What are the patterns for handling async form validation?

Implement debounced validation calls, handle loading states, cache validation results when appropriate. Consider race conditions and cancellation of pending validation requests.

How do you handle form submission with file uploads?

Use FormData for file uploads, handle upload progress, implement proper error handling and retry logic. Consider chunked uploads for large files and proper cleanup of file references.

How do you handle form internationalization?

Implement proper label and error message translations, handle different date/number formats, consider right-to-left languages. Use proper localization libraries and handle cultural differences.

What are the patterns for implementing form autosave functionality?

Implement debounced save function, handle save states and errors, provide user feedback. Consider conflict resolution and offline capabilities. Handle cleanup of autosave timers.

How do you handle form state management with Context or Redux?

Implement proper actions and reducers for form state, handle form namespacing, consider performance implications. Balance local vs global state for form data.

What are the considerations for handling form performance with large datasets?

Implement virtualization for large lists, optimize validation runs, use proper memoization. Consider chunking large forms and implementing progressive loading.

How do you implement custom select or autocomplete components?

Handle controlled component behavior, implement proper keyboard navigation, manage dropdown state and positioning. Consider accessibility and mobile device support.

What are the patterns for handling form submission retry logic?

Implement exponential backoff, handle different error types, maintain submission state. Consider user feedback during retries and proper cleanup of retry attempts.

What are the best practices for handling form security?

Implement CSRF protection, validate inputs server-side, handle sensitive data properly, prevent XSS attacks. Consider authentication state and proper permissions checking.

What are the patterns for handling form optimization in SSR?

Handle initial form state hydration, prevent flash of uncontrolled inputs, implement proper client-side validation initialization. Consider SEO implications and performance optimization.

What is route-based code splitting and how is it implemented?

Use React.lazy and Suspense with React Router to load components dynamically. Implement per-route code splitting for better performance and smaller initial bundle size.

How do you implement route transitions?

Use React Transition Group with React Router. Implement enter/exit animations, handle route-based transitions, and manage transition states properly.

What is server-side rendering with React Router?

Use StaticRouter instead of BrowserRouter for SSR. Handle location context, match routes on server, and manage data loading. Consider hydration and state management.

How do you implement breadcrumbs?

Use route configuration and current location to generate breadcrumbs. Handle dynamic segments, maintain breadcrumb state, and implement proper navigation.

How do you handle route guards?

Implement higher-order components or custom Route components for protection. Handle authentication, authorization, and redirect flows appropriately.

How do you handle scroll restoration?

Implement custom scroll behavior using useEffect. Handle scroll position per route, manage scroll restoration, and implement smooth scrolling.

How do you handle route-based code splitting with prefetching?

Implement React.lazy with prefetching strategies. Handle component preloading, manage loading states, and optimize performance.

What is memory router?

MemoryRouter keeps history in memory (not in URL). Useful for testing and non-browser environments. Maintains routing state without URL changes.

How do you test routing logic?

Use MemoryRouter for testing, mock route matches and history. Test navigation, protected routes, and route parameters. Implement comprehensive test cases.

How do you optimize large lists in React?

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.

What is the impact of context on performance?

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.

How do you optimize React Router performance?

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.

How do you optimize form performance in React?

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

What are the best practices for state management performance?

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

What is the role of Web Workers in React performance?

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.

What are the performance considerations for animations?

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

How do you implement performance monitoring?

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

What is the impact of ErrorBoundary on performance?

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

How do you optimize server-side rendering performance?

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

How do you implement efficient data structures in React?

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

What are the performance implications of using Context?

Context triggers re-renders in all consuming components when its value changes. Optimize by splitting contexts, using memoization, and considering component structure. Avoid putting frequently changing values in context.

How do you optimize context with memo?

Use React.memo on consuming components, memoize context value with useMemo, implement proper value comparison. Consider component structure and update patterns.

What are context selectors and how do you implement them?

Context selectors help consume specific parts of context to prevent unnecessary re-renders. Implement using custom hooks, memoization, and proper state structure.

What are the patterns for combining Context with Reducers?

Use useReducer with Context for complex state management, implement proper action dispatching, handle state updates efficiently. Similar to Redux pattern but lighter weight.

How do you handle async operations with Context?

Combine Context with useEffect for async operations, handle loading and error states, implement proper state updates. Consider async patterns and error boundaries.

What is context composition and when should you use it?

Compose multiple contexts to separate concerns, improve maintainability, and optimize performance. Use when different parts of the app need different subsets of global state.

What are the common pitfalls when using Context?

Overusing context, unnecessary re-renders, improper value memoization, context hell (too many nested providers). Consider alternatives and proper architecture.

What are the patterns for handling form state with Context?

Use context for form state management, implement proper validation, handle field updates efficiently. Consider form complexity and performance requirements.

How do you handle context in TypeScript?

Define proper types for context values, use generic types when needed, implement type checking. Consider type safety and proper interface definitions.

How do you handle context persistence?

Implement storage synchronization, handle hydration, manage persistence lifecycle. Consider storage options and state reconciliation.

How do you handle context cleanup and disposal?

Implement proper cleanup in effects, handle unmount scenarios, manage resource disposal. Consider memory leaks and cleanup timing.

What are the patterns for handling dynamic contexts?

Create contexts dynamically, handle context creation lifecycle, manage dynamic providers. Consider performance and maintenance implications.

How do you implement error recovery mechanisms?

Implement retry logic, state reset mechanisms, fallback UI, and proper error clearing. Consider user experience and recovery workflows.

How do you handle errors in React hooks?

Use try-catch in effects, implement error states, handle cleanup properly, consider custom hooks for error handling. Cannot use error boundaries directly in hooks.

How do you handle errors in Redux/state management?

Implement error reducers, handle async action errors, provide error states in store, consider middleware for error handling. Handle global vs local error states.

What are the best practices for error boundary placement?

Place boundaries strategically to isolate failures, consider component hierarchy, implement granular error handling. Balance between too many and too few boundaries.

How do you handle errors in React Suspense?

Use Error Boundaries with Suspense, handle loading errors, implement fallback UI, manage timeout scenarios. Consider data fetching errors.

What are the patterns for error handling in HOCs?

Implement error handling logic in HOCs, wrap components with error boundaries, handle prop validation errors. Consider composition of error handling HOCs.

How do you handle errors in React portals?

Use error boundaries around portals, handle portal-specific errors, manage cleanup on errors. Consider modal and overlay error scenarios.

How do you implement graceful degradation in error scenarios?

Provide fallback functionality, implement feature detection, handle browser compatibility issues. Consider progressive enhancement approaches.

How do you handle errors in server-side rendering?

Implement SSR-specific error handling, manage hydration errors, handle state reconciliation issues. Consider client-server error differences.

How do you handle memory leaks and cleanup errors?

Implement proper cleanup in useEffect, handle component unmounting, manage resource disposal. Consider async operation cancellation.

What are the strategies for error monitoring in production?

Implement error tracking services, collect error metrics, analyze error patterns, set up alerts. Consider privacy and performance implications.

How do you implement error tracking and analytics?

Integrate error tracking services, collect relevant error data, implement proper error categorization. Consider privacy and compliance requirements.

What are the best practices for testing error scenarios?

Test error boundaries, simulate different error conditions, verify error recovery, implement comprehensive test cases. Consider edge cases and error combinations.

How do you test custom hooks?

Use @testing-library/react-hooks with renderHook, test different scenarios and state changes, verify hook behavior and side effects. Consider proper cleanup and isolation.

How do you test React components with Redux?

Provide test store using Provider, mock store state and actions, test component integration with Redux. Consider proper store setup and cleanup.

How do you implement integration tests in React?

Test component interactions, data flow between components, state management integration. Focus on user workflows and feature completeness. Consider proper test isolation.

What are the strategies for testing error boundaries?

Simulate errors to test boundary behavior, verify fallback UI rendering, test error recovery. Consider different error scenarios and component hierarchy.

What are the best practices for mocking in React tests?

Mock external dependencies, API calls, and complex functionality. Use jest.mock() appropriately, maintain mock clarity. Consider partial mocking and mock cleanup.

How do you test accessibility in React components?

Use jest-axe for accessibility testing, verify ARIA attributes, test keyboard navigation. Consider screen reader compatibility and accessibility guidelines.

What are the patterns for testing animations and transitions?

Test animation triggers and completion, verify state changes during transitions, mock timers appropriately. Consider animation cleanup and timing issues.

How do you test performance optimizations?

Test render counts, verify memoization effectiveness, check optimization implementations. Consider performance measurement and monitoring in tests.

What are the strategies for testing file uploads?

Mock File API, test upload handlers, verify file validation and processing. Consider different file types and error scenarios.

How do you implement E2E testing in React?

Use Cypress or Playwright for end-to-end testing, test complete user flows, verify application integration. Consider test stability and maintenance.

How do you test React portals?

Test portal rendering and content, verify portal functionality and events. Consider DOM structure and cleanup.

How do you test React suspense and lazy loading?

Test loading states, verify component lazy loading, check suspense fallbacks. Consider network conditions and timing.

What are the patterns for testing state management?

Test state updates and transitions, verify state synchronization, check state persistence. Consider complex state scenarios and side effects.

How do you implement visual regression testing?

Use tools like Percy or Chromatic, compare visual changes, maintain visual consistency. Consider different viewport sizes and browser compatibility.

What are the performance implications of different styling approaches?

CSS-in-JS can impact runtime performance, CSS Modules have build-time overhead, inline styles prevent browser optimizations. Consider bundle size, runtime performance, and caching strategies.

How do you implement CSS-in-JS with TypeScript?

Use proper type definitions for styled components, implement theme typing, handle prop types for styled components. Consider type safety and proper inference.

How do you handle CSS specificity in React applications?

Use CSS Modules for scoping, implement proper class naming conventions, manage specificity hierarchy. Consider cascade and inheritance implications.

How do you implement RTL support in React styling?

Use CSS logical properties, implement directional styles, handle bidirectional text properly. Consider cultural differences and layout implications.

How do you handle CSS transitions with React Router?

Implement page transition animations, handle route-based styles, manage transition states. Consider performance and user experience.

What are the patterns for implementing styled system props?

Use style props for component customization, implement consistent prop interfaces, handle style composition. Consider type safety and documentation.

How do you optimize CSS delivery in React applications?

Implement critical CSS, handle code splitting, optimize load performance. Consider caching strategies and resource hints.

What are the approaches to handling CSS-in-JS server-side rendering?

Handle style extraction, implement proper hydration, manage style injection. Consider performance and flash of unstyled content.

How do you handle dynamic styling based on data?

Implement data-driven styles, handle dynamic classes and properties, manage style updates. Consider performance and maintainability.

What are the patterns for implementing design tokens?

Define and manage design tokens, implement token-based styling system, handle theme variations. Consider maintainability and consistency.

What are the approaches to testing styled components?

Test style rendering, verify theme integration, check dynamic styles. Consider snapshot testing and visual regression testing.

What are the performance optimization best practices in React?

Use React.memo for expensive components, implement proper key usage, avoid unnecessary re-renders, use proper dependency arrays in hooks, lazy load components, and implement code splitting.

What are the recommended patterns for API integration?

Implement proper data fetching patterns, handle loading and error states, implement caching strategies, maintain proper separation of concerns, and consider API state management.

What are the best practices for accessibility?

Follow ARIA guidelines, implement proper keyboard navigation, maintain proper heading hierarchy, provide proper alt texts, and implement proper focus management.

What are the best practices for type safety?

Use TypeScript or PropTypes, implement proper type definitions, maintain type consistency, handle type edge cases, and consider type inference optimization.

What are the recommended patterns for context usage?

Use context appropriately for global state, implement proper provider organization, optimize context updates, avoid context overuse, and consider performance implications.

What are the best practices for code reusability?

Implement proper component composition, create reusable hooks, maintain proper abstraction levels, implement proper HOC patterns, and consider code sharing strategies.

What are the best practices for security?

Prevent XSS attacks, handle sensitive data properly, implement proper authentication/authorization, validate inputs, and consider security implications in data handling.

What are the recommended patterns for performance monitoring?

Implement proper performance metrics, use React DevTools effectively, monitor render performance, track user interactions, and consider performance optimization strategies.

What are the best practices for code splitting?

Implement proper lazy loading, use dynamic imports effectively, handle loading states, optimize bundle size, and consider code splitting strategies.

What are the best practices for internationalization?

Implement proper i18n solution, handle translations effectively, manage locale changes, consider RTL support, and implement proper internationalization patterns.

What are the recommended patterns for state persistence?

Implement proper storage strategies, handle state rehydration, manage persistence lifecycle, consider offline support, and implement proper persistence patterns.

What are the recommended patterns for progressive enhancement?

Implement proper fallbacks, handle feature detection, maintain core functionality, consider browser support, and implement proper enhancement strategies.

What are the best practices for deployment?

Implement proper build process, optimize asset delivery, handle environment variables, implement proper CI/CD, and consider deployment strategies.

How do you handle authentication with APIs?

Manage tokens securely, handle token refresh, implement interceptors for requests, manage auth state. Consider session management and security implications.

How do you implement request caching?

Use caching libraries (React Query, SWR), implement local storage caching, handle cache invalidation, manage cache lifecycle. Consider cache strategies and freshness.

What are the patterns for handling real-time data?

Implement WebSocket connections, handle Socket.IO integration, manage real-time state updates, handle connection states. Consider reconnection strategies and data consistency.

What are the best practices for API request optimization?

Implement request debouncing/throttling, batch requests when possible, optimize payload size, use proper caching strategies. Consider performance and bandwidth usage.

What are the patterns for handling offline functionality?

Implement service workers, handle offline storage, manage sync queues, handle conflict resolution. Consider offline-first architecture and data synchronization.

How do you implement optimistic updates?

Update UI immediately before API confirmation, handle rollback on failure, manage temporary state, implement proper error recovery. Consider user experience and data consistency.

What are the patterns for handling API rate limiting?

Implement request queuing, handle rate limit errors, manage retry strategies, provide user feedback. Consider backend limitations and optimization strategies.

What are the best practices for API security?

Implement proper authentication/authorization, handle CORS, prevent XSS attacks, manage sensitive data. Consider security best practices and vulnerabilities.

How do you implement API request queuing?

Handle sequential requests, manage request priority, implement queue processing logic. Consider error handling and queue management.

What are the best practices for API performance monitoring?

Track request times, monitor error rates, implement performance metrics, analyze bottlenecks. Consider monitoring tools and optimization strategies.

What are the patterns for handling GraphQL in React?

Use Apollo Client or other GraphQL clients, manage queries and mutations, handle caching, implement proper error handling. Consider GraphQL-specific optimizations.

How do you handle API request batching?

Implement request combining, manage batch processing, handle response correlation, optimize network usage. Consider performance and complexity trade-offs.

What are the patterns for handling API state persistence?

Implement local storage caching, handle state rehydration, manage persistence lifecycle. Consider storage strategies and state management.

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Technical Interview Questions

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Next.js

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Apollo GraphQL

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SQL

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HR Interview Questions

HR

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Sales Manager

Account Manager

Content Marketing Manager

Sales Representative

Digital Marketing Manager

Brand Manager

MBA Operations

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Social Media Manager

Sales Engineer

Customer Success Manager

MBA Supply Chain

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MBA Accounting

MBA Finance

Why Prepare with Stark.ai for reactjs Interviews?

Role-Specific Questions

  • Frontend Developer
  • Full-Stack Developer
  • React Engineer

Expert Insights

  • Detailed explanations to demystify React concepts.

Real-World Scenarios

  • Hands-on exercises for creating and debugging React components.

How Stark.ai Helps You Prepare for reactjs Interviews

Mock Interviews

Simulate ReactJS-specific interview scenarios.

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Practice Coding Questions

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Resume Optimization

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Tips to Ace Your reactjs Interviews

Understand React Fundamentals

Be fluent in JSX, state management, and the component lifecycle.

Build Reusable Components

Practice creating modular and reusable UI components.

Stay Updated

Familiarize yourself with React hooks, Context API, and the latest React features.

Demonstrate Real Projects

Showcase personal or collaborative projects using ReactJS.

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