Top 30 Most Asked Node.js Interview Questions and Answers (Complete Guide – 2025 & 2026)

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Node.js continues to be one of the most powerful and widely adopted runtime environments in the world of backend development. As companies shift to microservices, cloud-native development, serverless architecture, and scalable applications, the demand for Node.js developers is soaring in 2025 and is projected to grow even more in 2026.

Whether you are preparing for a Node.js Developer, Backend Engineer, Full Stack Developer, or JavaScript Developer role, interviewers increasingly focus on real-world scenario-based questions instead of only theory. This comprehensive guide covers the Top 30 Most Asked Node.js Interview Questions and Answers tailored for 2025–2026.

Let’s begin!

⭐ What Is Node.js and Why Is It Important for 2025–2026?

Node.js is a server-side JavaScript runtime environment built on Chrome’s V8 engine. It allows developers to build scalable network applications using JavaScript outside the browser.

Why Node.js is booming in 2025–2026:

  • Microservices adoption is at an all-time high
  • Companies prefer JavaScript full-stack developers
  • Node.js powers scalable SaaS and enterprise apps
  • Cloud-native architecture relies heavily on Node.js
  • Fast API development and real-time app support (WebSockets)

This makes Node.js one of the top 5 backend technologies used worldwide.

Top 30 Most Asked Node.js Interview Questions and Answers (2025–2026)

These questions are categorized for freshers, experienced developers, and scenario-based problem-solving.

🟩 SECTION 1: NODE.JS INTERVIEW QUESTIONS AND ANSWERS FOR FRESHERS

1. What is Node.js?

Answer:
Node.js is an open-source, cross-platform JavaScript runtime environment that executes JavaScript code outside of a browser. It is built on Google’s V8 Engine and is known for its event-driven, non-blocking I/O model.

Key benefits:

  • Fast performance
  • Lightweight
  • Scalable
  • Ideal for real-time applications

2. What is the V8 Engine in Node.js?

Answer:
The V8 engine is Google’s open-source JavaScript engine used in Chrome. Node.js uses V8 to execute JavaScript directly on the machine instead of the browser.

It converts JavaScript → Machine code → Executes.

3. What are the features of Node.js?

Answer:

  • Asynchronous & non-blocking
  • Single-threaded event loop
  • High scalability
  • Built-in modules
  • NPM ecosystem with thousands of packages
  • Real-time application support

4. What is NPM?

Answer:
NPM (Node Package Manager) is the default package manager for Node.js. It contains over 2 million packages.

Uses:

  • Install packages
  • Manage project dependencies
  • Create custom packages

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

FeatureJavaScriptNode.js
EnvironmentBrowserServer-side
File AccessNoYes
ModulesES ModulesCommonJS & ES Modules
PurposeFront-end scriptsBackend APIs & servers

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

Answer:
The event loop is the heart of Node.js. It handles asynchronous operations in a single thread.

Its job:

  • Processes callbacks
  • Executes asynchronous tasks
  • Sends operations to appropriate system threads

7. What is a Callback Function?

Answer:
A callback is a function passed into another function to be executed when an asynchronous operation completes.

Example:

fs.readFile('file.txt', (err, data) => {
   console.log(data);
});

8. What is a Promise in Node.js?

Answer:
A Promise represents an asynchronous operation that can be:

  • Pending
  • Resolved
  • Rejected

9. What is Async/Await in Node.js?

Answer:
Async/Await is a modern JavaScript syntax built on Promises that makes asynchronous code look synchronous.

Example:

async function test() {
  const data = await getData();
}

10. What is Middleware in Node.js?

Answer:
Middleware functions are functions in Express.js that execute between incoming requests and outgoing responses.

Types:

  • Application-level
  • Router-level
  • Error-handling
  • Built-in

🟩 SECTION 2: NODE.JS INTERVIEW QUESTIONS FOR EXPERIENCED DEVELOPERS

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

Featureprocess.nextTick()setImmediate()
ExecutesBefore next event loop tickAt the end of current cycle
PriorityHigherLower

12. What is the EventEmitter in Node.js?

Answer:
EventEmitter is a class from Node’s events module that enables event-based programming.

Example:

const EventEmitter = require('events');
const emitter = new EventEmitter();

emitter.on('start', () => console.log("Started"));
emitter.emit('start');

13. What are Streams in Node.js?

Answer:
Streams are used to handle continuous data flows.

Types:

  • Readable
  • Writable
  • Duplex
  • Transform

Example: Reading file as stream:

fs.createReadStream('data.txt');

14. What is the difference between Synchronous and Asynchronous functions?

SynchronousAsynchronous
BlockingNon-blocking
Waits for resultUses callbacks/promises
Slow for I/OFast for I/O

15. What is a Buffer in Node.js?

Answer:
Buffer is a temporary storage area for binary data used in streams.
Example:

const buf = Buffer.from("Hello");

16. Explain CommonJS vs ES Modules in Node.js.

CommonJSES Modules
require()import
module.exportsexport
SynchronousAsynchronous
Default in Node <=12Default in Node >=14

17. How does Node.js handle child processes?

Using child_process module:

  • spawn
  • exec
  • fork

Example:

const {spawn} = require('child_process');
spawn('ls', ['-lh']);

18. What is Cluster Module in Node.js?

Answer:
Cluster allows scaling Node.js apps by creating multiple worker processes sharing a single server port.

19. What is the Purpose of package.json?

It stores:

  • Project metadata
  • Dependencies
  • Scripts
  • Version info
  • License

20. What is JWT Authentication in Node.js?

JWT → JSON Web Token
Used for secure user authentication.

Flow:

  1. User logs in
  2. Server generates JWT
  3. Client stores token
  4. Token is verified for protected routes

🟩 SECTION 3: ADVANCED NODE.JS INTERVIEW QUESTIONS (2025–2026)

21. How do you improve performance in a Node.js application?

Techniques include:

  • Use clustering
  • Use load balancers
  • Optimize event loop
  • Reduce middleware
  • Use async/await
  • Use caching (Redis)
  • Use message queues (RabbitMQ, Kafka)
  • Use connection pooling

22. What is Rate Limiting? How do you implement it?

Answer:
Rate limiting restricts the number of requests a client can make in a time window.

Used to prevent:

  • DDOS attacks
  • API abuse

Implementation:

const rateLimit = require('express-rate-limit');
app.use(rateLimit({windowMs: 60000, max: 100}));

23. What is CORS in Node.js?

Answer:
CORS (Cross-Origin Resource Sharing) controls which domains can access server resources.

Implementation:

app.use(cors());

24. Explain Microservices Architecture in Node.js.

Node.js is ideal for microservices because:

  • Lightweight
  • Fast
  • Works well with Docker/Kubernetes
  • Built for async I/O
  • Easy to scale horizontally

25. What is Load Balancing in Node.js?

Load balancing distributes traffic among multiple server instances.

Technologies:

  • NGINX
  • HAProxy
  • Node cluster module
  • Cloud load balancers (AWS ELB)

🟩 SECTION 4: NODE.JS SCENARIO-BASED INTERVIEW QUESTIONS

26. Scenario: Your API is slow. How do you fix it?

Answer:

  • Enable caching (Redis)
  • Optimize database queries
  • Use async functions
  • Use PM2 cluster mode
  • Reduce JSON payload size
  • Use CDN
  • Use profiling tools

27. Scenario: How do you handle file uploads in Node.js?

Use Multer:

const multer = require('multer');
const upload = multer({dest: 'uploads/'});
app.post('/upload', upload.single('file'));

28. Scenario: Your Node.js application crashes. How do you debug it?

Steps:

  • Use console.log()
  • Use Node debugger
  • Use VSCode debug tools
  • Use PM2 logs
  • Use error boundaries
  • Use try/catch and async error handlers

29. Scenario: You need to connect Node.js with MongoDB. How?

Using Mongoose:

mongoose.connect("mongodb://localhost/testdb");

30. Scenario: You need to build a real-time chat app. Which module do you use?

Socket.IO
Example:

io.on('connection', socket => {
  console.log("User connected");
});

🟩 Extra 2025–2026 Node.js Interview Questions (Bonus for Mastery)

Here are additional advanced questions interviewers ask frequently:

  • What is event delegation in Node.js?
  • What is WebSocket vs SSE?
  • Explain Redis caching
  • What are Observables in Node.js?
  • What is a message queue?
  • Explain OAuth2 in Node.js

Want these added? I can include them.

🟩 Best Practices for Node.js in 2025–2026

  • Use TypeScript for large apps
  • Use environment variables (.env)
  • Apply secure headers (Helmet.js)
  • Use database indexing
  • Implement logging (Winston, Bunyan)
  • Apply API versioning
  • Use Docker + Kubernetes for deployment
  • Apply CI/CD pipelines (GitHub Actions, Jenkins)

🟩 Final Thoughts

This complete, in-depth guide provides the Top 30 Most Asked Node.js Interview Questions and Answers for 2025–2026 along with explanations, examples, and real-world scenarios.

Whether you are:

  • A fresher
  • A mid-level developer
  • An advanced backend engineer
  • Preparing for FAANG or product-based companies

This article will help you boost your interview performance and confidence.

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