Top 30 Node.js Interview Questions and Answers in 2025 (Beginner-Friendly Guide)

You’ve landed an interview for your dream developer job. You’re pumped, confident… until the interviewer says:

“So, tell me about Node.js and how it's different from traditional backend frameworks.”

Your heart skips a beat.
What even is Node.js? 😨

If that scenario sounds even remotely familiar, you’re in the right place.

Whether you're prepping for your first developer job or brushing up on your backend skills, this guide will walk you through the top 30 Node.js interview questions and answers for 2025 – all explained in plain English, with examples and tips along the way. 🎯

🌟 Why Learn Node.js?

Node.js is one of the most in-demand backend technologies in 2025. Here's why:

• ✅ It’s JavaScript on the server – so frontend developers can become full-stack devs more easily.
• ⚡ It's fast thanks to its non-blocking I/O model.
• 🧩 It has a huge ecosystem of libraries (npm).
• 💼 It's used by companies like Netflix, Uber, PayPal, and LinkedIn.

Whether you’re a fresh grad or changing careers, knowing Node.js gives you a serious advantage.

🔹 Section 1: Basics & Fundamentals

1. What is Node.js?

Answer:
Node.js is a JavaScript runtime built on Chrome’s V8 engine. It lets you run JavaScript outside the browser, typically to build server-side applications.

🔍 Think of it as the “engine” under the hood that lets JavaScript work on the backend.

2. Why is Node.js single-threaded?

Answer:
Node.js uses a single-threaded event loop to handle multiple clients without creating a new thread for each. This makes it lightweight and fast, especially for I/O operations.

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

Answer:
The event loop is what allows Node.js to perform non-blocking I/O operations. It keeps checking for tasks, executes them when ready, and handles callbacks efficiently.

🧠 Think of it as a waiter taking multiple orders without waiting at each table.

4. What are callbacks?

Answer:
A callback is a function passed into another function as an argument, to be executed later.

fs.readFile('file.txt', function(err, data) {
  if (err) throw err;
  console.log(data.toString());
});

5. What is npm?

Answer:
npm stands for Node Package Manager. It’s the default package manager for Node.js, used to install and manage libraries.

📦 Example: npm install express

🔹 Section 2: Working with Modules

6. What are Node.js modules?

Answer:
Modules are reusable blocks of code. Node.js has built-in modules like fs (file system), and you can create your own.

7. Difference between CommonJS and ES6 modules?

8. How do you export and import a module in Node.js?

// file: math.js
module.exports.add = (a, b) => a + b;

// file: app.js
const math = require('./math');
console.log(math.add(2, 3)); // 5

9. What is the difference between require() and import?

Answer:

• require() is synchronous and CommonJS.
• import is asynchronous and ES6-based.

Node.js supports both now, but import requires .mjs or "type": "module" in package.json.

10. What is package.json?

Answer:
It's the heart of any Node.js project – defining metadata, dependencies, scripts, and versioning.

🔹 Section 3: Asynchronous Programming

11. What is the difference between synchronous and asynchronous code?

Answer:

• Synchronous: Waits for each task to complete before moving on.
• Asynchronous: Doesn’t wait. Uses callbacks, promises, or async/await.

12. What is a Promise in Node.js?

const promise = new Promise((resolve, reject) => {
  resolve("Success!");
});

Answer:
A promise represents the eventual result of an async operation – either resolved or rejected.

13. What is async/await?

Answer:
A cleaner way to write async code using promises.

async function getData() {
  const data = await fetchData();
  console.log(data);
}

14. What are Streams in Node.js?

Answer:
Streams allow reading or writing data piece-by-piece (chunks) instead of loading it all at once. Great for big files.

15. What are the different types of streams?

• Readable
• Writable
• Duplex (both)
• Transform (modifies data)

🔹 Section 4: Server & Networking

16. How do you create a simple HTTP server in Node.js?

const http = require('http');
http.createServer((req, res) => {
  res.end('Hello World!');
}).listen(3000);

17. What is Express.js?

Answer:
Express is a minimal and flexible web framework built on Node.js. It simplifies routing, middleware, and server logic.

🚀 It's the most popular Node.js framework today.

18. How do you handle routing in Express?

app.get('/', (req, res) => {
  res.send('Home Page');
});

19. What is middleware in Express?

Answer:
Functions that have access to request, response, and next in the request-response cycle.

app.use((req, res, next) => {
  console.log('Middleware executed');
  next();
});

20. How do you handle errors in Express?

app.use((err, req, res, next) => {
  res.status(500).send('Something broke!');
});

🔹 Section 5: Advanced & Practical

21. What is clustering in Node.js?

Answer:
Clustering allows you to spawn multiple Node.js processes to take advantage of multi-core systems.

22. What are environment variables in Node.js?

console.log(process.env.NODE_ENV);

Used to manage configs like dev/prod mode, API keys, etc.

23. What is process.nextTick()?

Answer:
It defers a function to execute after the current operation completes but before the event loop continues.

24. What are child processes in Node.js?

Used to spawn subprocesses to handle CPU-intensive tasks.

const { exec } = require('child_process');
exec('ls', (err, stdout) => console.log(stdout));

25. Difference between spawn and fork?

• spawn: launches a new process.
• fork: used specifically to spawn new Node.js processes and communicate with them.

26. What is the difference between process.exit() and process.kill()?

• process.exit(): Gracefully exits.
• process.kill(): Sends a signal to terminate the process.

27. How do you debug a Node.js app?

Use the built-in --inspect flag with Chrome DevTools or VSCode debugger.

28. What is CORS and how do you enable it?

Answer:
CORS = Cross-Origin Resource Sharing. Use middleware like cors to enable:

const cors = require('cors');
app.use(cors());

29. What is JWT in Node.js?

Answer:
JWT (JSON Web Token) is used to securely transmit information, usually for authentication.

30. How do you connect Node.js to a database (like MongoDB)?

const mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/mydb');

✅ Bonus: 3 Quick Interview Q&As

Q1: What is the use of __dirname in Node.js?

It gives the absolute path of the directory containing the current file.

Q2: What is the difference between res.send() and res.json() in Express?

• res.send(): Sends a response (string, buffer, object).
• res.json(): Sends JSON with proper headers.

Q3: Is Node.js good for CPU-intensive apps?

Not ideal! Node.js is better suited for I/O-heavy tasks. Use worker threads or child processes for CPU-bound tasks.

🎯 Final Thoughts

You just walked through 30 of the most common Node.js interview questions for 2025 – with plain-English answers and real examples.

Here’s your action plan:

• ⭐ Bookmark this guide
• 🔁 Revisit and practice the code snippets
• 💬 Join a community or comment below to ask questions

💬 Question for You:

What was the most confusing Node.js concept for you when starting out – and how did you overcome it?
Drop your thoughts in the comments! 👇

Happy coding and good luck with your interview! 🚀💼