Top 50 Node.js Interview Questions and Answers

Node.js is a widely used runtime environment for building scalable backend applications. Whether you are preparing for a job interview or want to strengthen your understanding, mastering key concepts of Node.js is essential. Below are 50 frequently asked interview questions with concise answers.

1. What is Node.js?

Node.js is a JavaScript runtime that allows execution of JavaScript code outside the browser, commonly used for backend development.

2. What is the difference between Node.js and JavaScript?

JavaScript is a programming language, while Node.js is a runtime environment that enables JavaScript to run on the server side.

3. Is Node.js single-threaded?

Yes, Node.js follows a single-threaded, event-driven architecture with non-blocking I/O operations for handling multiple requests efficiently.

4. What kind of API functions does Node.js support?

Node.js supports both synchronous (blocking) and asynchronous (non-blocking) API functions.

5. What is a module in Node.js?

A module in Node.js is a reusable block of code that provides specific functionality and can be imported into other files.

6. What is npm and its advantages?

npm (Node Package Manager) is the default package manager for Node.js, offering benefits such as dependency management and version control.

7. What is middleware?

Middleware functions execute between request and response cycles, handling tasks like logging, authentication, and data processing.

8. How does Node.js handle concurrency despite being single-threaded?

Node.js uses asynchronous, non-blocking operations and event loops to handle multiple tasks concurrently.

9. What is control flow in Node.js?

Control flow refers to the sequence in which statements and functions execute, helping manage asynchronous operations.

10. What is the event loop in Node.js?

The event loop is a mechanism that processes asynchronous tasks by continuously checking for and executing callback functions.

11. What are the main disadvantages of Node.js?

Single-threaded nature, making CPU-intensive tasks challenging
Preference for NoSQL databases
Rapid API changes leading to instability

12. What is REPL in Node.js?

REPL (Read-Eval-Print Loop) is an interactive environment for executing and debugging Node.js code.

13. How to import a module in Node.js?

Use the require() function to import external modules.

14. What is the difference between Node.js and AJAX?

Node.js is a server-side runtime, while AJAX is a client-side technique for asynchronous web updates.

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

package.json is a configuration file that stores project metadata, dependencies, and scripts.

16. What is the most popular Node.js framework?

Express.js is the most popular framework due to its simplicity and scalability.

17. What are promises in Node.js?

Promises are objects that handle asynchronous operations, providing a cleaner alternative to callbacks.

18. What is event-driven programming in Node.js?

Event-driven programming synchronizes events using event loops and callback functions.

19. What is a buffer in Node.js?

A buffer is a temporary storage area for binary data.

20. What are streams in Node.js?

Streams handle continuous data flows and optimize reading and writing operations.

21. Explain the crypto module in Node.js.

The crypto module provides cryptographic functionalities like encryption and hashing.

22. What is callback hell?

Callback hell refers to deeply nested callbacks, making code hard to read and maintain.

23. Explain the use of the timers module in Node.js.

The timers module schedules code execution using setTimeout() and setImmediate().

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

process.nextTick(): Executes callbacks at the start of the next event loop cycle.
setImmediate(): Executes callbacks at the end of the current event loop cycle.

25. What is the difference between setTimeout() and setImmediate()?

setTimeout(): Executes a callback after a specified delay.
setImmediate(): Executes a callback immediately after I/O events.

26. What is the difference between spawn() and fork()?

spawn(): Runs a new process.
fork(): Creates a new instance of the existing process for parallel execution.

27. Explain the use of the passport module in Node.js.

Passport.js is used for authentication, supporting multiple sign-in methods.

28. What is fork in Node.js?

Forking creates child processes for parallel execution.

29. What are the three methods to avoid callback hell?

Use async/await
Use Promises
Use Generators

30. What is body-parser in Node.js?

Body-parser is middleware that parses incoming request bodies.

31. What is CORS in Node.js?

CORS (Cross-Origin Resource Sharing) allows requests from different domains.

32. Explain the TLS module in Node.js.

The TLS module provides an implementation of the TLS and SSL protocols for secure connections.

33. What is a cluster in Node.js?

Clusters enable Node.js to utilize multiple CPU cores by creating child processes.

34. How to manage sessions in Node.js?

Use the express-session module to store session data on the server.

35. Explain the types of streams in Node.js.

Readable Streams
Writable Streams
Duplex Streams (both readable and writable)
Transform Streams (modify data during transmission)

36. How can we implement authentication and authorization in Node.js?

Use Passport.js for authentication and JWT (JSON Web Tokens) for authorization.

37. Explain the packages used for file uploading in Node.js.

Multer is the most popular middleware for handling file uploads.

38. How to handle database connections in Node.js?

Use database drivers like MySQL and libraries like Mongoose for MongoDB.

39. How to read command-line arguments in Node.js?

Use process.argv to access command-line arguments.

40. What are child processes in Node.js?

Child processes allow concurrent execution by creating subprocesses that run independently.

This article can be used as a comprehensive guide for Node.js interviews. Do you want any modifications or formatting improvements? 😊

Here are 10 more important Node.js interview questions to enhance the article:

41. What is the difference between process.env and process.argv?

process.env: Stores environment variables used by the Node.js application.
process.argv: Stores command-line arguments passed to the script.

42. What is the difference between synchronous and asynchronous programming in Node.js?

Synchronous: Code executes sequentially, blocking the execution until the current task completes.
Asynchronous: Code executes without blocking, allowing multiple tasks to run concurrently.

43. How does error handling work in Node.js?

Node.js uses:

try...catch for synchronous errors.
Callbacks with error-first pattern (e.g., function(err, data)).
Promises and async/await with try...catch for asynchronous errors.

44. What is the difference between process and thread in Node.js?

Process: An independent execution unit with its own memory and resources.
Thread: A lightweight execution unit within a process, sharing memory and resources.

45. What is the difference between ES6 import and CommonJS require()?

require(): CommonJS module system, used in Node.js.
import: ES6 module system, requires "type": "module" in package.json.

46. What is the purpose of the dns module in Node.js?

The dns module provides DNS resolution functions, allowing domain name lookups, hostname resolution, and IP address retrieval.

47. What is the difference between app.use() and app.get() in Express.js?

app.use(): Registers middleware globally for all routes.
app.get(): Defines a route handler that responds to GET requests.

48. How does Node.js handle memory management?

Node.js manages memory using:

Garbage collection (handled by V8 engine).
Heap and stack memory allocation for objects and function execution.
Buffer management for binary data.

49. How can you secure a Node.js application?

Use HTTPS for secure communication.
Implement input validation and sanitization to prevent SQL Injection and XSS.
Use Helmet.js for setting secure HTTP headers.
Encrypt sensitive data with bcrypt.js.
Implement JWT authentication for secure user sessions.

50. What is the role of worker threads in Node.js?

Worker threads enable Node.js to execute CPU-intensive tasks in separate threads, preventing the event loop from being blocked.

Top 50 NODE JS Interview Question and Answer in 2025 | NODE JS Interview Question

Top 50 NODE JS Interview Question and Answer in 2025 | NODE JS Interview Question: