Node.js Interview Questions

Lesson content

Topics ✅ What is Node.js? ✅ V8 Engine ✅ Reactor Pattern ✅ npm ✅ module.exports / ES Modules ✅ Forever ✅ Synchronous JavaScript ✅ Assert ✅ Stub ✅ Event Loop ✅ Closures ✅ Promises ✅ Hoisting ✅ Scope ✅ this ✅ Arrow Functions ✅ Async/Await ✅ Prototype ✅ Currying ✅ Event Delegation ✅ REST API ✅ GraphQL ✅ gRPC ✅ Protobuf ✅ Server-Sent Events (SSE) ✅ WebSockets Important Node.js Interview Topics Still Missing For a 5+ years / Senior Node.js Developer / Lead Developer interview, I recommend adding these topics. 1. Node.js Architecture Single Thread Worker Threads Cluster Module Child Process libuv Thread Pool 2. Event Loop (Advanced) Call Stack Callback Queue Microtask Queue process.nextTick() setImmediate() Timers Phase Poll Phase Check Phase 3. Streams Readable Writable Duplex Transform Pipe Backpressure 4. Buffers Buffer Binary Data Encoding UTF-8 5. Memory Management Heap Stack Garbage Collection Memory Leak Heap Snapshot 6. Performance Event Loop Blocking CPU Intensive Tasks Caching Redis Compression Gzip Load Balancer 7. Security JWT OAuth CORS Helmet CSRF XSS SQL Injection Rate Limiting 8. Express Advanced Middleware Error Middleware Custom Middleware Validation Multer Morgan Compression 9. Authentication JWT Refresh Token Access Token Cookie Session Passport.js 10. Database Connection Pooling Transactions Indexing Pagination Aggregation ORM vs Query Builder 11. Design Patterns Singleton Factory Repository Dependency Injection Strategy Observer 12. API Design REST Best Practices Versioning Pagination Filtering Sorting HATEOAS Idempotency 13. Testing Jest Supertest Mock Spy Stub Unit Testing Integration Testing E2E Testing 14. Deployment PM2 Forever Docker Nginx CI/CD GitHub Actions Kubernetes 15. Logging Winston Pino Morgan Log Rotation 16. Scaling Horizontal Scaling Vertical Scaling Sticky Sessions Redis Adapter Message Queue 17. Message Queues RabbitMQ Kafka BullMQ Redis Queue SQS 18. AWS EC2 S3 SES SQS Lambda CloudWatch 19. TypeScript Interface Type Generic Decorators Utility Types 20. Coding Questions Promise implementation EventEmitter implementation LRU Cache Debounce Throttle Deep Clone Flatten Array Retry API Rate Limiter Frequently Asked Senior Node.js Interview Questions Explain the Event Loop in detail. How does libuv work? Why is Node.js single-threaded? What is the difference between process.nextTick() and setImmediate() ? Explain Streams and Backpressure. What causes memory leaks in Node.js? How do you optimize a slow Node.js API? Cluster vs Worker Threads. How do you scale Node.js to millions of users? Explain the Reactor Pattern. How do you secure REST APIs? How do JWT Refresh Tokens work? How do you implement caching? How do you design a production-ready Node.js application? How do you debug memory leaks? Explain CommonJS vs ES Modules. How do you implement file uploads? Explain connection pooling. How do you monitor Node.js in production? What happens internally when node app.js is executed? Recommendation Since you're preparing for Senior/Lead Node.js interviews , expand these notes into a structured guide of around 120–150 interview questions with: Beginner, Intermediate, and Advanced sections. Detailed answers. Code examples. Common follow-up questions. Real production scenarios. Performance and optimization tips. This would cover nearly everything expected in interviews for experienced Node.js developers.