Which Node JS Interview Questions to prepare for experienced professionals?

For experienced professionals, Node.js interview questions tend to focus on advanced concepts, architectural decisions, performance optimization, and hands-on experience with real-world issues. Here’s a breakdown of essential Node.js interview topics and questions to prepare for senior-level roles:

1. Event Loop and Asynchronous Programming

• Question: Describe the Node.js event loop. How does it handle asynchronous operations?
• Question: What is the difference between setImmediate(), process.nextTick(), and setTimeout()?
• Question: Explain how you would handle asynchronous control flow in Node.js, and discuss the benefits of async/await over Promises and callbacks.
• Skills Tested: Understanding of the event loop, asynchronous programming patterns, and the nuances of Node.js’s concurrency model.

2. Performance Optimization

• Question: How would you optimize the performance of a Node.js application with high CPU usage?
• Question: Describe how you would use clustering in Node.js to improve performance.
• Question: How do you monitor memory leaks in Node.js, and which tools would you use to diagnose and fix them?
• Skills Tested: Experience in optimizing CPU-bound tasks, using clusters for scaling, memory management, and profiling with tools like Node.js inspector, Chrome DevTools, or pm2.

3. Scalability and System Design

• Question: How would you design a scalable microservices architecture using Node.js?
• Question: What are the advantages and disadvantages of using microservices with Node.js versus a monolithic architecture?
• Question: How would you handle inter-service communication in a microservices environment?
• Skills Tested: Ability to design and implement scalable architectures, knowledge of microservices, RESTful API, gRPC, and message queues.

4. Error Handling

• Question: How would you handle errors in Node.js, especially in asynchronous code?
• Question: What strategies would you use for centralized error handling in a large Node.js application?
• Question: How do you handle uncaught exceptions in Node.js, and why is this important?
• Skills Tested: Proficiency in error-handling strategies, using try/catch with async/await, and implementing global error-handling middleware.

5. Security Best Practices

• Question: What are some common security vulnerabilities in Node.js applications, and how do you prevent them?
• Question: Explain how you would secure API endpoints in a Node.js application.
• Question: How do you protect against Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF) attacks in Node.js?
• Skills Tested: Knowledge of security practices like data validation, secure headers (Helmet), CSRF protection, and implementing CORS.

6. Middleware and Express.js

• Question: Explain the concept of middleware in Express.js. How does it work, and how do you create custom middleware?
• Question: How would you implement rate limiting for an API in Express.js?
• Question: Describe your approach to handling CORS in a Node.js API.
• Skills Tested: Middleware implementation, Express.js, handling API security concerns, and preventing abuse through rate limiting and CORS.

7. Handling Large Data and Streams

• Question: What are streams in Node.js, and how do they improve data handling performance?
• Question: Explain how you would handle backpressure in a Node.js application that uses streams.
• Question: How do you use streams to read and write large files efficiently in Node.js?
• Skills Tested: Proficiency with streams, managing backpressure, and handling large data sets in a memory-efficient way.

8. Testing and Debugging

• Question: What is your approach to unit and integration testing in Node.js applications?
• Question: Which testing libraries do you prefer for Node.js, and why?
• Question: How do you handle mocking and stubbing dependencies when testing?
• Skills Tested: Familiarity with testing frameworks (e.g., Mocha, Chai, Jest), writing unit and integration tests, mocking dependencies, and using test doubles.

9. Database Management

• Question: How would you implement database connection pooling in Node.js, and why is it important?
• Question: What are the trade-offs between using an SQL and NoSQL database in a Node.js application?
• Question: How would you handle database transactions in a Node.js application?
• Skills Tested: Knowledge of relational and non-relational databases (e.g., MongoDB, PostgreSQL), database connection pooling, and transaction management.

10. API Design and Websockets

• Question: Describe how you would design a RESTful API using Node.js and Express.
• Question: How do WebSockets work, and when would you use them in a Node.js application?
• Question: How do you handle versioning and documentation for your APIs?
• Skills Tested: RESTful API design, WebSocket for real-time communication, and handling API versioning and documentation.

11. Authentication and Authorization

• Question: Explain the differences between session-based and token-based authentication in Node.js.
• Question: How would you implement JWT-based authentication in a Node.js API?
• Question: What are the advantages and disadvantages of using OAuth for third-party authentication?
• Skills Tested: Experience with authentication and authorization techniques, JWT, OAuth, and secure session management.

12. Package Management and Dependency Handling

• Question: How do you manage dependencies in a Node.js project? What’s your approach to handling dependency vulnerabilities?
• Question: Explain semantic versioning and why it’s important in Node.js development.
• Question: How do you decide between using npm and Yarn for dependency management?
• Skills Tested: Knowledge of package management, semantic versioning, handling dependency security issues, and choosing package managers.

13. Configuration and Environment Management

• Question: How do you manage environment variables and sensitive information in a Node.js application?
• Question: Describe your approach to configuring an application for different environments (development, testing, production).
• Question: How do you handle configuration changes in a production environment without redeploying the application?
• Skills Tested: Proficiency in environment variable management, dotenv, configuration management across environments, and secure handling of sensitive information.

14. Deployment, CI/CD, and DevOps

• Question: Describe your Node.js deployment process and the tools you use for CI/CD.
• Question: How do you handle logging and monitoring in a Node.js application in production?
• Question: What are some best practices for deploying a Node.js application on cloud platforms like AWS or Azure?
• Skills Tested: Knowledge of deployment strategies, CI/CD pipelines (e.g., Jenkins, GitHub Actions), cloud deployment, and production monitoring.

15. Serverless Architecture

• Question: What are the benefits and trade-offs of using serverless architecture with Node.js?
• Question: How would you deploy a Node.js function to AWS Lambda?
• Question: Explain how you would handle cold starts and execution time limits in a serverless function.
• Skills Tested: Experience with serverless architecture, AWS Lambda, cold start optimization, and designing applications for serverless environments.

Preparation Tips

1. Review Advanced JavaScript: Deepen your understanding of closures, async programming, event loop, and scope management.
2. Build a Project: Work on a real-world project to solidify concepts like error handling, authentication, and database interactions.
3. Stay Updated: Node.js evolves rapidly, so stay informed about the latest features and updates.
4. Practice Testing and Debugging: Use tools like Mocha, Chai, Jest, and the Node.js inspector to develop strong testing and debugging skills.
5. Study System Design: For senior roles, system design knowledge is essential. Review design patterns, scalable architectures, and distributed systems.

By focusing on these advanced topics and questions, you’ll be prepared to demonstrate your in-depth Node.js knowledge, problem-solving skills, and experience working with complex Node.js applications.