React Interview Cheat Sheet

1. What problem does React solve compared to directly manipulating the DOM?

Entry Full Answer →

2. What is JSX and why do we use it in React?

Entry Full Answer →

3. Why must React components start with a capital letter?

Entry Full Answer →

4. What is the purpose of the createRoot API introduced in React 18?

Entry Full Answer →

5. What is the difference between a Component and an Element in React?

Entry Full Answer →

6. What is the use of React Fragment?

Entry Full Answer →

7. Why do we use keys in lists?

Entry Full Answer →

8. What happens if we use the array index as a key?

Entry Full Answer →

9. What is the difference between props and state?

Entry Full Answer →

10. Can a component modify its own props?

Entry Full Answer →

11. What does useState() return?

Entry Full Answer →

12. Why doesn’t updating state directly trigger a re-render?

Entry Full Answer →

13. What is the purpose of useEffect?

Entry Full Answer →

14. What happens if you forget dependencies in useEffect?

Entry Full Answer →

15. What is controlled vs uncontrolled component in forms?

Entry Full Answer →

16. What is React Strict Mode and why is it useful?

Entry Full Answer →

17. What is Concurrent Rendering in React 18?

Entry Full Answer →

18. What is useId introduced in React 18?

Entry Full Answer →

19. What is the difference between useEffect and useLayoutEffect?

Entry Full Answer →

20. What are React Server Components?

Entry Full Answer →

21. How does React reconcile two virtual DOM trees during re-rendering?

Junior Full Answer →

22. Why is the render process pure but the commit phase is not in React?

Junior Full Answer →

23. What problem do React Server Components solve?

Junior Full Answer →

24. Why is data fetching in useEffect considered an anti-pattern in React 18+?

Junior Full Answer →

25. What is the difference between batching in React 17 and React 18?

Junior Full Answer →

26. Why does React warn when state is updated during rendering?

Junior Full Answer →

27. What is the purpose of the useTransition hook?

Junior Full Answer →

28. How does React decide which components to re-render?

Junior Full Answer →

29. Why must React state remain immutable?

Junior Full Answer →

30. What happens when state setters run inside loops outside event handlers?

Junior Full Answer →

31. What is the Render Prop pattern?

Junior Full Answer →

32. What problem does React Context solve?

Junior Full Answer →

33. How does React Context differ from Redux?

Junior Full Answer →

34. What does useReducer help solve?

Junior Full Answer →

35. Why should objects or arrays not be placed directly in dependency arrays?

Junior Full Answer →

36. What is memoization in React and when is React.memo useful?

Junior Full Answer →

37. What is the difference between useMemo and useCallback?

Junior Full Answer →

38. Why is lifting state up used in React?

Junior Full Answer →

39. What are controlled inputs and why can they hurt performance?

Junior Full Answer →

40. What is Suspense and why was it introduced?

Junior Full Answer →

41. How does Suspense differ in data fetching vs code splitting?

Junior Full Answer →

42. What is hydration in React?

Junior Full Answer →

43. What is partial hydration?

Junior Full Answer →

44. How does React handle synthetic events?

Junior Full Answer →

45. What is useDeferredValue used for?

Junior Full Answer →

46. How does React 19 improve hydration?

Junior Full Answer →

47. What is useOptimistic in React 19?

Junior Full Answer →

48. What is the difference between the use hook and await in React 19?

Junior Full Answer →

49. Why shouldn’t data fetching occur in constructors or render methods?

Junior Full Answer →

50. What is an error boundary?

Junior Full Answer →