Fundamentals

01

What is Node.js and why do developers use it?

easy

02

What is non-blocking I/O and why is it important?

easy

03

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

easy

04

What is the global object in Node.js?

easy

05

What is the process object in Node.js?

medium

18

What are the built-in (core) modules in Node.js?

medium

35

What is the Buffer class and when do you use it?

medium

36

What is the path module and why do you always need it?

medium

49

What is the child_process module and when do you use it?

hard

63

What is pagination and how do you implement it properly?

hard

66

What are environment variables and how do you manage them?

medium

71

What is TypeScript with Node.js and why should you use it?

medium

73

What is distributed tracing and how do you add it to Node.js?

hard

74

What is the health check endpoint and why is it essential?

hard

77

What is file upload handling and what are the security considerations?

hard

83

What is the difference between 'require' caching and singleton pattern?

hard

86

What is deep cloning vs shallow cloning in Node.js?

medium

88

What is the difference between null and undefined in Node.js?

easy

89

How do you check if a variable is an array in Node.js?

easy

90

What is the use of 'strict mode' in Node.js?

easy

91

What is the difference between map() and forEach()?

easy

92

What is the purpose of package-lock.json?

easy

93

What is the difference between devDependencies and dependencies?

easy

94

What is semantic versioning (SemVer)?

easy

95

What does the ^ (caret) and ~ (tilde) mean in package.json?

easy

96

What is the difference between app.listen() and http.createServer()?

medium

97

How do you handle unhandled promise rejections globally?

medium

98

What is the purpose of the 'os' module?

easy

99

What is the 'crypto' module used for?

medium

100

How can you read a large file without blocking the event loop?

medium

Architecture

06

What is single-threaded in Node.js and is it a problem?

easy

07

What is V8 and what role does it play in Node.js?

easy

08

What is libuv and what does it do?

easy

09

What is the Event Loop in Node.js?

medium

10

What are the phases of the Event Loop?

hard

14

What is the Thread Pool in Node.js?

hard

50

What is AsyncLocalStorage and why is it useful?

hard

55

What is input validation and how do you do it properly?

medium

56

What is the Repository Pattern and why use it?

hard

57

What is dependency injection and how does it help in Node.js?

hard

60

What is the Observer pattern with EventEmitter — practical patterns?

hard

67

What is the proper folder structure for a Node.js project?

hard

75

What are API versioning strategies in Node.js?

hard

79

What are microservices and how does Node.js fit in?

hard

81

What is request context and how do you pass it through your app?

hard

82

What is the SOLID principle applied to Node.js?

hard

84

What is the difference between REST and GraphQL APIs in Node.js?

hard

Asynchrony

11

What is the exact execution order: sync → nextTick → Promise → setTimeout → setImmediate?

hard

12

What is process.nextTick() and when should you use it?

medium

13

What is the difference between process.nextTick() and setImmediate()?

medium

26

What are callbacks and what is callback hell?

easy

27

What is util.promisify() and when do you use it?

medium

28

What is the difference between sequential and parallel async operations?

hard

29

How do you handle errors properly with async/await in Node.js?

hard

30

What is the race condition problem in async code and how do you fix it?

hard

62

What is the difference between synchronous and asynchronous error handling patterns?

hard

Modules

15

What is the CommonJS module system (require/module.exports)?

easy

16

What is the difference between module.exports and exports?

medium

17

What are ES Modules (import/export) in Node.js?

medium

Streams

19

What are streams in Node.js?

medium

20

What is pipe() in streams and how does it work?

medium

21

What is backpressure in streams and why does it matter?

hard

22

How do you create a custom Transform stream?

hard

Events

23

What is EventEmitter in Node.js?

medium

24

What is the 'error' event and why is it special?

medium

25

What is the maximum number of listeners and memory leak warning?

hard

Express

31

How does Express.js middleware work?

easy

32

What is the exact order Express executes middleware and routes?

medium

33

How do you handle errors globally in an Express app?

hard

34

What is the difference between app.use() and app.get()/post()/put()/delete()?

medium

Performance

37

What is the Cluster module and how does it use multiple CPU cores?

hard

38

What are Worker Threads and how are they different from Cluster?

hard

39

What causes memory leaks in Node.js and how do you prevent them?

hard

40

What is graceful shutdown and why is it critical?

hard

47

What is caching and how do you implement it with Redis?

hard

53

What is rate limiting and how do you implement it?

medium

58

What is the Circuit Breaker pattern in Node.js?

hard

59

What is PM2 and why use it in production?

medium

61

What is logging in production Node.js and what should you use?

medium

70

What are common Node.js performance anti-patterns to avoid?

hard

80

What is compression and how does it improve API performance?

hard

85

What is debounce and throttle in the context of Node.js?

hard

Auth

41

How does JWT authentication work in Node.js?

medium

42

How do you hash passwords correctly in Node.js?

medium

43

What are the most important security practices for Node.js?

hard

44

What is CORS and how do you configure it in Node.js?

medium

72

What is npm audit and how do you handle security vulnerabilities?

hard

76

What is session management vs JWT and which should you use?

hard

Database

45

What is connection pooling and why is it critical?

medium

46

What is the N+1 query problem and how do you fix it?

medium

48

What are database transactions and when do you need them?

hard

78

What is database indexing and why does it matter for Node.js apps?

hard

Scalability

51

What are job queues and why are they essential?

hard

54

How do you schedule recurring tasks (cron jobs) in Node.js?

medium

68

What is the difference between horizontal and vertical scaling in Node.js?

hard

Real-time

52

What is WebSocket and how do you implement real-time features?

medium

69

What is Server-Sent Events (SSE) and how is it different from WebSockets?

hard

Testing

64

How do you test Node.js/Express APIs?

hard

65

What is mocking in tests and how do you mock database calls?

hard

87

What is TDD (Test Driven Development) and should I use it?

medium