50 React.js Interview Questions (2025 Latest)

1. React Basics

1. What is React.js, and why is it used?
2. What are the key features of React?
3. What is JSX in React?
4. How does React handle the Virtual DOM?
5. What is the difference between functional and class components?
6. What are React fragments, and why are they used?
7. What is the role of key in lists in React?
8. How does React update the UI efficiently?
9. What is reconciliation in React?
10. How is React different from frameworks like Angular and Vue?

2. React Hooks

11. What are React Hooks, and why are they introduced?
12. How does the useState hook work?
13. What is the useEffect hook used for?
14. How can you clean up side effects in useEffect?
15. What is the difference between useEffect and componentDidMount?
16. How does the useContext hook work?
17. What is the useRef hook, and when should you use it?
18. How does useMemo optimize performance?
19. What is useCallback, and how is it different from useMemo?
20. How can you create a custom React Hook?

3. State Management & Context API

21. What is state in React, and how is it managed?
22. What is the difference between local state and global state?
23. How does the Context API work in React?
24. What are the limitations of Context API compared to Redux?
25. How does React Redux work for state management?
26. What is the difference between Redux and React’s Context API?
27. What are the key concepts of Redux (actions, reducers, store)?
28. What is Redux Toolkit, and why is it recommended?
29. How does React Query help in state management?
30. What are some alternatives to Redux for global state management?

4. React Performance Optimization

31. What are some ways to optimize performance in React applications?
32. How does lazy loading work in React?
33. What is React.memo(), and how does it improve performance?
34. How does the React Profiler tool help in performance debugging?
35. What is the significance of React Fiber?
36. What are concurrent features in React 18?
37. How does React.lazy() work with Suspense?
38. What is Server-Side Rendering (SSR) in React?
39. What is hydration in React, and when is it useful?
40. How does React handle re-renders, and how can you prevent unnecessary re-renders?

5. Advanced Topics & Best Practices

41. What is Next.js, and how is it different from React?
42. What are higher-order components (HOCs) in React?
43. What is Prop Drilling, and how can it be avoided?
44. What is the difference between controlled and uncontrolled components?
45. How does React handle event handling and synthetic events?
46. What is the difference between useEffect and useLayoutEffect?
47. How does React handle form validation?
48. What are React Portals, and when should you use them?
49. How does Error Boundary work in React?
50. What new features were introduced in React 18+?