React Architect: 50+ Senior & Lead Interview Deep-Dives (2026)

I. REACT FUNDAMENTALS & ADVANCED PATTERNS (15 Questions)

1. Explain the React Fiber architecture and how it differs from the previous stack reconciler. How does this affect performance optimization strategies?

   • Follow-up: Describe how time slicing and suspense work under Fiber architecture.

2. Implement a custom hook useDeepCompareEffect that only triggers when deep equality changes. Compare its performance implications vs useEffect with dependency arrays.

   • Follow-up: When would you use useMemo vs useCallback vs custom memoization?

3. Design a render-prop based component that handles authentication state. Then refactor it to use hooks. Discuss the trade-offs between both patterns.

   • Follow-up: How do render props affect React DevTools debugging experience?

4. Explain the subtle differences between useLayoutEffect and useEffect with concrete examples where each is appropriate.

   • Follow-up: How do these hooks behave during server-side rendering?

5. Implement error boundaries with recovery mechanisms. How would you design a system to track and report these errors at scale?

   • Follow-up: Why don't error boundaries catch errors in event handlers?

6. Create a higher-order component that injects internationalization. Then implement the same using Context + hooks. Compare bundle size implications.

   • Follow-up: How would you implement code splitting with HOCs vs hooks?

7. Explain React's synthetic event system and its performance implications for large applications.

   • Follow-up: When would you use native events instead?

8. Design a portal-based modal system that manages focus trapping, ARIA attributes, and stacking context.

   • Follow-up: How would you handle multiple concurrent modals?

9. Implement a virtualized list component from scratch. Discuss optimization techniques for variable height items.

   • Follow-up: How would you handle dynamic content loading within the viewport?

10. Explain Concurrent Features in React 18+: startTransition, useDeferredValue, and Suspense for Data Fetching.

    • Follow-up: How do these features impact UX metrics like INP (Interaction to Next Paint)?

11. Design a compound component pattern for a data table with sortable, filterable columns and selectable rows.

    • Follow-up: How would you make it accessible for screen readers?

12. Implement a custom useReducer with middleware support similar to Redux.

    • Follow-up: How would you handle side effects in this system?

13. Explain the "lifting state up" pattern and when you might choose React Context instead.

    • Follow-up: How does this decision impact component re-renders?

14. Create a drag-and-drop system using the HTML5 Drag API with React.

    • Follow-up: How would you make this work on touch devices?

15. Implement a real-time collaborative text editor using Operational Transformation or CRDTs with React.

    • Follow-up: How would you handle offline synchronization?

II. STATE MANAGEMENT & DATA FLOW (10 Questions)

16. Compare Redux Toolkit, Zustand, Jotai, and Recoil for a large enterprise application. What criteria would you use to choose?

    • Follow-up: How do these affect bundle size and initial load time?

17. Design a normalized state structure for an e-commerce application with products, categories, users, and orders.

    • Follow-up: How would you handle real-time inventory updates?

18. Implement optimistic updates for a shopping cart with rollback on error.

    • Follow-up: How would you persist the optimistic state during page reloads?

19. Design a state synchronization system between multiple browser tabs using BroadcastChannel or localStorage events.

    • Follow-up: How would you handle merge conflicts?

20. Explain the trade-offs between client-side state, server state, and URL state.

    • Follow-up: When would you use React Router's state vs Redux?

21. Implement a finite state machine for a multi-step checkout process using XState.

    • Follow-up: How would you visualize and debug state transitions?

22. Design a caching strategy for GraphQL queries with normalized caching.

    • Follow-up: How would you handle cache invalidation for nested mutations?

23. Create a real-time dashboard with WebSocket connections managing multiple data streams.

    • Follow-up: How would you handle connection drops and reconnection strategies?

24. Implement a middleware for Redux that handles API requests with retry logic and exponential backoff.

    • Follow-up: How would you add request deduplication?

25. Design a form management system that handles complex validation, cross-field dependencies, and async validation.

    • Follow-up: How would you implement draft auto-save functionality?

III. PERFORMANCE OPTIMIZATION (10 Questions)

26. Analyze a React application's performance using Chrome DevTools and React Profiler. What metrics would you prioritize?

    • Follow-up: How would you identify "wasted renders"?

27. Implement code splitting for a large application using dynamic imports, React.lazy, and Suspense.

    • Follow-up: How would you preload critical chunks?

28. Design a performance monitoring system that tracks Core Web Vitals in production.

    • Follow-up: How would you attribute performance issues to specific components?

29. Optimize a large list rendering 10,000 items with virtualization, memoization, and web workers for sorting/filtering.

    • Follow-up: How would you handle memory management for infinite scrolling?

30. Explain the impact of Context API on performance and strategies to mitigate unnecessary re-renders.

    • Follow-up: When would you split contexts vs use selectors?

31. Implement a custom useMemo with a size-limited LRU cache.

    • Follow-up: How would you determine the optimal cache size?

32. Design a bundle analysis pipeline that identifies optimization opportunities.

    • Follow-up: How would you enforce bundle size limits in CI/CD?

33. Optimize a React application for mobile devices with limited CPU and memory.

    • Follow-up: How would you implement adaptive rendering based on device capabilities?

34. Explain tree shaking in modern bundlers and how to ensure it works effectively with React.

    • Follow-up: How do barrel exports affect tree shaking?

35. Implement a performance budget system with regression detection.

    • Follow-up: How would you prioritize performance fixes?

IV. TESTING & QUALITY (5 Questions)

36. Design a testing strategy covering unit, integration, and E2E tests for a React application. What would be your test pyramid distribution?

    • Follow-up: How would you mock complex dependencies like WebSockets?

37. Implement a custom render function for Testing Library that includes providers (Redux, Router, Theme).

    • Follow-up: How would you test custom hooks in isolation?

38. Create a visual regression testing pipeline for a component library.

    • Follow-up: How would you handle dynamic content in snapshots?

39. Design an accessibility testing strategy that integrates into CI/CD.

    • Follow-up: How would you ensure ongoing compliance, not just initial testing?

40. Implement contract testing for a micro-frontend architecture.

    • Follow-up: How would you handle breaking changes?

V. ARCHITECTURE & SCALABILITY (10 Questions)

41. Design a micro-frontend architecture for a large enterprise application. Compare Module Federation vs single-spa vs iframes.

    • Follow-up: How would you handle shared dependencies and versioning?

42. Create a design system architecture with theming, dark mode, and CSS-in-JS vs CSS Modules vs utility-first CSS.

    • Follow-up: How would you ensure consistency across teams?

43. Design a server-side rendering setup with streaming, hydration optimization, and partial hydration.

    • Follow-up: How would you handle third-party scripts that break SSR?

44. Implement a plugin architecture allowing teams to extend a core application.

    • Follow-up: How would you ensure plugin isolation and security?

45. Design a build system supporting multiple deployment targets (web, mobile web, PWA, desktop with Electron).

    • Follow-up: How would you share code while maintaining platform-specific optimizations?

46. Create an A/B testing framework that supports multivariate testing and gradual rollouts.

    • Follow-up: How would you ensure type safety for experiment configurations?

47. Design a feature flag system with runtime configuration and gradual rollouts.

    • Follow-up: How would you clean up old feature flags?

48. Implement a monorepo structure with efficient CI/CD pipelines.

    • Follow-up: How would you handle shared dependency updates?

49. Design an offline-first PWA with background sync and IndexedDB for data persistence.

    • Follow-up: How would you handle schema migrations?

50. Create a migration plan from class components to functional components with hooks.

    • Follow-up: How would you ensure zero downtime during migration?

VI. LEADERSHIP & SYSTEM DESIGN (5 Questions)

51. How would you structure a frontend team of 10 engineers working on a large React application? What processes would you implement?

• Follow-up: How would you mentor mid-level engineers to senior level?

52. Design an RFC (Request for Comments) process for technical decisions in a React codebase.

• Follow-up: How would you handle disagreements about technical direction?

53. Create a technical debt assessment framework and prioritization matrix for a legacy React application.

• Follow-up: How would you secure resources for addressing technical debt?

54. Design a frontend incident response process for production issues.

• Follow-up: How would you implement feature toggles for rapid rollback?

55. How would you evaluate and adopt new React features or third-party libraries in an enterprise environment?

• Follow-up: What criteria would you use for build vs buy decisions?

Interview Evaluation Framework

When conducting interviews with these questions, assess candidates on:

1. Depth of Technical Knowledge - Understanding of React internals

2. Practical Problem Solving - Ability to translate theory to code

3. System Design Thinking - Considering scalability, maintenance, and team workflows

4. Performance Awareness - Optimization mindset and metrics-driven approach

5. Leadership & Communication - Ability to explain complex concepts and make trade-offs explicit