Node.js Interview Questions and Answers (Basic to Advanced)

Introduction

Node.js is a powerful JavaScript runtime built on Chrome's V8 engine, enabling developers to build scalable and efficient applications. Whether you're a beginner or an experienced developer, preparing for Node.js interviews is essential. This blog covers Basic, Intermediate, and Advanced Node.js interview questions along with their answers.

Basic Node.js Interview Questions

1. What is Node.js?

Answer: Node.js is a JavaScript runtime environment that allows developers to execute JavaScript code outside the browser. It is built on the V8 engine and uses an event-driven, non-blocking I/O model, making it ideal for building scalable applications.

2. How does Node.js handle asynchronous operations?

Answer: Node.js uses an event-driven, non-blocking I/O model. It handles asynchronous operations using:

• Callbacks
• Promises
• Async/Await
• Event Loop

3. What is NPM in Node.js?

Answer: NPM (Node Package Manager) is the default package manager for Node.js. It is used to install, manage, and share JavaScript libraries and dependencies.

Command to install a package:

npm install express

4. Explain the difference between CommonJS and ES Modules.

Answer:

Intermediate Node.js Interview Questions

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

Answer: The Event Loop in Node.js is responsible for handling asynchronous operations. It follows the following phases:

• Timers Phase (setTimeout, setInterval)
• Pending Callbacks
• Idle, Prepare
• I/O Polling
• Check Phase (setImmediate callbacks)
• Close Callbacks

6. How does Middleware work in Express.js?

Answer: Middleware functions in Express.js are used for:

• Logging requests
• Authentication
• Error handling
• Response modifications

Example:

const express = require('express');
const app = express();

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

7. What is a Stream in Node.js?

Answer: Streams are used to handle large amounts of data efficiently. They operate in four modes:

1. Readable Streams (fs.createReadStream)
2. Writable Streams (fs.createWriteStream)
3. Duplex Streams (both readable and writable)
4. Transform Streams (modifies data during reading/writing)

Example:

const fs = require('fs');
const readStream = fs.createReadStream('file.txt', 'utf8');
readStream.on('data', chunk => console.log(chunk));

Advanced Node.js Interview Questions

8. How does Cluster Module improve performance?

Answer: The Cluster module allows Node.js to fork multiple worker processes using os.cpus().length, distributing the load efficiently.

Example:

const cluster = require('cluster');
const os = require('os');

if (cluster.isMaster) {
    for (let i = 0; i < os.cpus().length; i++) {
        cluster.fork();
    }
} else {
    require('./server');
}

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

Answer:

• process.nextTick(): Executes before the next event loop iteration.
• setImmediate(): Executes in the next event loop cycle.

Example:

console.log('Start');
process.nextTick(() => console.log('NextTick'));
setImmediate(() => console.log('SetImmediate'));
console.log('End');

10. How to handle memory leaks in Node.js?

Answer: Memory leaks can occur due to improper handling of objects, closures, or event listeners. Solutions:

• Use Heap Snapshots and Memory Profiling tools.
• Remove unnecessary event listeners (removeListener).
• Use WeakMap for caching.

Conclusion

Mastering Node.js requires a strong understanding of its core concepts. These questions and answers will help you ace your Node.js interviews at different levels. Keep practicing, and happy coding!