Node.js Interview Questions

1. What is Node.js and How Does it Work?

2. How Does the Event Loop Work in Node.js?

3. What is npm in Node.js?

4. CommonJS vs ES Modules in Node.js

5. What is Express.js?

6. What is Middleware in Express.js?

7. What is the EventEmitter in Node.js?

8. What are Streams in Node.js?

9. What are Buffers in Node.js?

10. Blocking vs Non-Blocking Code in Node.js

11. What are Error-First Callbacks in Node.js?

12. What is the process Object in Node.js?

13. How Do Environment Variables Work in Node.js?

14. What is the Cluster Module in Node.js?

15. What are Worker Threads in Node.js?

16. What are Child Processes in Node.js?

17. What is libuv in Node.js?

18. What is the difference between package.json and package-lock.json?

19. How Does the fs Module Work in Node.js?

20. How Do You Create an HTTP Server in Node.js?

21. How Do You Handle CORS in Node.js?

22. How Does JWT Authentication Work in Node.js?

23. What is util.promisify in Node.js?

24. process.nextTick vs setImmediate in Node.js

25. What are Global Objects in Node.js?

26. How Do You Handle Uncaught Exceptions in Node.js?

27. How Do You Build a REST API with Express.js?

28. What are Caching Strategies in Node.js?

29. What are Security Best Practices in Node.js?

30. How Do You Detect Memory Leaks in Node.js?

31. What is the Event Loop in Node.js?

32. What is a Callback in Node.js?

33. What are Streams in Node.js?

34. What is the Cluster Module in Node.js?

35. What is package.json in Node.js?

36. What is Nodemon in Node.js?

37. What is REST in Express.js?

38. What is JWT Authentication in Node.js?

39. What is the require Function in Node.js?

40. What is EventEmitter in Node.js?

41. What is a Buffer in Node.js and why does it exist?

42. What is process.env in Node.js and how do you use it for configuration?

43. What is the error-first callback pattern in Node.js?

44. What is the difference between Node.js and browser JavaScript?

45. Walk through the phases of the Node.js event loop and explain where each kind of callback actually runs.

46. How do you detect and diagnose event-loop blocking in a production Node.js service?

47. When would you choose worker_threads over child_process or cluster in Node.js?

48. What is back-pressure in Node.js streams, and why should you use pipeline instead of pipe?

49. What are the safety pitfalls of Buffer allocation and slicing in Node.js?

50. How does AsyncLocalStorage propagate request context in Node.js, and what are its limits?

51. How do you implement graceful shutdown and connection draining in a Node.js HTTP service?

52. How would you diagnose a slow memory leak in a long-running Node.js process?

53. What practical problems do ESM loading and native addons cause in a Node.js codebase?

54. How should a production service handle uncaughtException versus unhandledRejection in Node.js?

55. How do HTTP keep-alive and agent pooling affect outbound request performance in Node.js?

56. What is diagnostics_channel in Node.js and when would you use it instead of monkey-patching?

57. How do you keep a Node.js project's dependency supply chain safe?

58. How do you cancel in-flight asynchronous work in Node.js with AbortController?

59. How would you process a very large JSON payload in Node.js without exhausting memory?

60. Why does a Node.js container get OOM-killed even though the heap looks fine, and how do you size it?

61. What runs on the libuv thread pool, and when would you change UV_THREADPOOL_SIZE?