Top 30 React Interview Questions Every Developer Must Know

Practice the top 30 React interview questions with this SEO-focused quiz covering JSX, props, state, hooks, effects, context, memoization, list keys, form handling, performance, and modern React architecture. Perfect for frontend developers preparing for React jobs, coding interviews, and production-ready application development. Topics Covered: 1. What is the primary purpose of React? 2. Which syntax extension is commonly used with React components? 3. What does a React component return? 4. How are data values passed from parent to child component? 5. What hook is used to add local component state? 6. When does `useEffect` run by default? 7. What does an empty dependency array mean in `useEffect`? 8. Why should each item in a rendered list have a key? 9. Which statement about React state updates is correct? 10. What is the main benefit of functional state updates? 11. What is lifting state up in React? 12. What is the purpose of `useMemo`? 13. What does `React.memo` help with? 14. Which hook provides a mutable value that does not trigger re-render? 15. What is a controlled component in React forms? 16. Why should hooks be called at the top level of components? 17. What is the purpose of cleanup in `useEffect`? 18. When is `useReducer` preferred over `useState`? 19. What does Context API primarily solve? 20. What is code splitting in React? 21. Why is `Suspense` used with lazy-loaded components? 22. What is the correct way to update arrays in React state? 23. What is the role of dependency arrays in hooks? 24. What is hydration in React applications? 25. What is the purpose of an Error Boundary? 26. Why can using index as key in dynamic lists be problematic? 27. What does `useCallback` help optimize? 28. How should side effects like API calls be handled in React? 29. What is a custom hook in React? 30. What is the key difference between `props` and `state`?