Fullstack Interview Questions and Answers

1. What are micro-frontends and how do they work?

Answer: Micro-frontends allow a large application’s UI to be split into smaller, independent frontend applications, similar to microservices in backend development. This enables modular development and easier scaling.

2. How do you optimize a React application for performance?

Answer:

• Code Splitting using React.lazy() and Suspense

• Memoization with useMemo and useCallback

• Virtualized Lists using react-window

• Avoiding unnecessary re-renders with React.memo

3. What is serverless architecture and when should you use it?

Answer: Serverless architecture allows developers to run backend logic using cloud functions (e.g., AWS Lambda, Firebase Functions) without managing servers. Ideal for event-driven applications like chatbots, authentication services, and APIs.

4. How do you implement SSR (Server-Side Rendering) in Next.js?

Answer: Use getServerSideProps() to fetch data on the server before rendering the page.

javascript

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export async function getServerSideProps() { const data = await fetchAPI(); return { props: { data } }; }

5. What are design patterns commonly used in Full Stack Development?

Answer:

• Singleton (ensures a single instance of a class)

• Factory (creates objects dynamically)

• Observer (subscribers receive updates when data changes)

• MVC (Model-View-Controller)

6. What is a GraphQL resolver?

Answer: A resolver is a function in GraphQL that handles fetching data for a particular query.

javascript

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const resolvers = { Query: { user: (_, { id }) => getUserById(id), }, };

7. How does load balancing improve web application performance?

Answer: Load balancing distributes incoming traffic across multiple servers, reducing downtime and improving scalability. Tools: Nginx, AWS ELB, HAProxy.

8. What is the Event Loop in Node.js and how does it work?

Answer: The Event Loop allows Node.js to handle non-blocking I/O operations by executing callbacks asynchronously.

9. What are web workers in JavaScript?

Answer: Web workers run JavaScript code in the background, preventing the main thread from blocking.

javascript

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const worker = new Worker('worker.js'); worker.postMessage('Start');

10. What is the difference between HTTP/2 and HTTP/3?

Answer:

• HTTP/2: Uses multiplexing, reducing latency.

• HTTP/3: Uses QUIC protocol for faster, more reliable connections.

11. How do you manage state in large-scale React applications?

Answer: Use Redux, Recoil, or Zustand for global state management.

12. What is a Reverse Proxy and how is it used in Full Stack Development?

Answer: A reverse proxy sits between clients and backend servers to improve security, caching, and load balancing.

13. How do you secure an API in a full stack application?

Answer:

• Use OAuth 2.0 for authentication.

• Implement rate limiting to prevent DDoS attacks.

• Use CORS headers properly.

• Secure requests with JWT tokens.

14. How does IndexedDB differ from LocalStorage?

Answer: IndexedDB is a NoSQL database in the browser, supporting large amounts of structured data, whereas LocalStorage only stores key-value pairs.

15. How do you ensure database transactions are atomic in a full stack application?

Answer: Use ACID principles and transactions in SQL databases.

sql

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BEGIN TRANSACTION; UPDATE accounts SET balance = balance - 100 WHERE id = 1; UPDATE accounts SET balance = balance + 100 WHERE id = 2; COMMIT;

16. What is the CAP theorem and how does it apply to databases?

Answer: The CAP theorem states that a distributed system can only achieve two out of three:

• Consistency (C)

• Availability (A)

• Partition Tolerance (P)

SQL databases focus on Consistency & Availability, while NoSQL databases prioritize Availability & Partition Tolerance.

17. How do you optimize a MongoDB database?

Answer:

• Use Indexes to speed up queries.

• Use Aggregation Pipelines for efficient data processing.

• Use Sharding for handling large datasets.

18. What is Continuous Deployment vs. Continuous Delivery?

Answer:

• Continuous Deployment: Code is automatically deployed to production after passing tests.

• Continuous Delivery: Code is ready for deployment but requires manual approval.

19. How do you handle WebSocket disconnections gracefully?

Answer:

• Implement reconnection logic with exponential backoff.

• Use heartbeats (ping/pong messages) to detect broken connections.

javascript

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const ws = new WebSocket('ws://example.com'); ws.onclose = () => setTimeout(reconnect, 5000);

20. What are Kubernetes and Docker, and how do they relate?

Answer:

• Docker packages applications into containers.

• Kubernetes orchestrates and manages multiple containers across clusters.

21. How do you implement caching in a full stack application?

Answer: Use Redis or Memcached to store frequently accessed data and reduce database load.

javascript

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redisClient.set('user_1', JSON.stringify(userData), 'EX', 3600);

22. What is CQRS (Command Query Responsibility Segregation)?

Answer: CQRS separates read and write operations, improving performance in complex applications.

23. How do you use WebRTC in a full stack application?

Answer: WebRTC enables real-time communication (video/audio streaming) between browsers.

javascript

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const peerConnection = new RTCPeerConnection(); peerConnection.createOffer().then(offer => sendOffer(offer));

24. What is a Service Worker and how does it enable offline functionality?

Answer: Service Workers act as a proxy between the browser and network, enabling offline caching and push notifications in Progressive Web Apps (PWAs).

25. How do you implement Blue-Green Deployment in a Full Stack application?

Answer: Blue-Green Deployment maintains two production environments:

• Blue (Current Live Version)

• Green (New Version for Testing)

Once the Green version is stable, traffic is switched over from Blue to Green seamlessly.