MERN Stack Developer interview Questions

My MERN Stack Interview — Frontend (React.js) Experience

Hey everyone! 👋

Recently, I appeared for a MERN Stack Developer interview, and I’d love to share all the React.js + Frontend questions that were asked.

⚛️ React.js & Frontend Questions

1. What is React, and what are Hooks?
2. Difference between useCallback, useMemo, and React.memo.
3. Explain useContext, useRef, and their real use cases.
4. Controlled vs Uncontrolled Components — difference & example.
5. Why do we use useState instead of updating variables directly?
6. Explain useReducer with an example.?
7. What is the purpose of React.lazy and Suspense?
8. How do you handle errors in React (try-catch, Error Boundary)?
9. How do you pass data between components?
10. What’s the purpose of a key in React?
11. How do you implement pagination in React?
12. What are Higher-Order Components (HOCs)?
13. Difference between Debouncing and Throttling.
14. When and where do you use clearInterval?
15. Difference between position: fixed and position: sticky.
16. How do you manage routes for Admin and User separately?
17. How do you keep form data after page refresh (localStorage / Redux)?
18. What’s the difference between CSR, SSR, SSG, and ISR (Next.js)?
19. Explain file-based routing in Next.js.
20. How do you handle API errors and loading states in React apps?
21. How do you optimize a large React app’s performance?
22. When do you use Context API vs Redux?
23. Explain React 19 features like Actions, useOptimistic, and useTransition.
24. What is a Custom Hook and when should you create one?
25. How do you start working when you receive a Figma design?
26. How do you manage image optimization in Next.js?
27. What’s the role of TypeScript in React development?
28. How do you prevent memory leaks in React components?