Top 50 Node JS Interview Questions And Answers

In this NodeJS tutorial complete guide, we will learn the top 50 Node JS Interview Questions and Answers that are often asked by recruiters.

Node.js is a popular open-source, cross-platform JavaScript runtime environment that has gained significant traction among developers worldwide. Its ability to handle large amounts of data and scale applications with ease has made it a popular choice for building server-side web applications.

If you are preparing for a Node.js interview, it’s important to have a good understanding of the key concepts and features of this technology.

In this article, we have compiled a list of the top 50 Node.js interview questions and answers to help you prepare for your interview and increase your chances of success.

These questions cover a wide range of topics, including Node.js basics, modules, events, streams, callbacks, and error handling, among others.

By studying these questions and answers, you’ll be better equipped to demonstrate your knowledge and skills in Node.js and ace your next job interview.

[Q1] What is Node.js, and what are its key features?

Node.js is an open-source, cross-platform JavaScript runtime environment that allows developers to run JavaScript on the server side. Its key features include event-driven architecture, non-blocking I/O, and a large and active developer community.

[Q2] What is Node.js and how does it differ from traditional web applications?

Node.js is a server-side JavaScript runtime environment that is built on top of the Chrome V8 JavaScript engine. It is different from traditional web applications in that it uses a non-blocking, event-driven I/O model that makes it ideal for building scalable, high-performance web applications.

[Q2] What is the difference between Node.js and JavaScript?

Node.js is a runtime environment for executing JavaScript code on the server side, while JavaScript is a programming language used for creating web applications.

Node.js and JavaScript are related but distinct technologies. Here are some key differences between them:

1. Execution environment: JavaScript is a programming language that is executed in a browser, while Node.js is a runtime environment that executes JavaScript code on the server side.
2. Access to resources: JavaScript running in a browser is sandboxed, which means it has limited access to the resources of the host computer, such as the file system and operating system. Node.js, on the other hand, is designed to have access to these resources, making it suitable for building server-side applications.
3. Modules: Node.js has its own module system that allows developers to create reusable code and share it across applications. JavaScript does not have a built-in module system, but modern web browsers support the import and export syntax for modular programming.
4. Event-driven architecture: Node.js is based on an event-driven architecture, which means it uses a single thread to handle multiple connections asynchronously. This allows Node.js to handle a large number of connections without blocking, making it well-suited for building scalable network applications. JavaScript running in a browser can also be event-driven, but the execution model is different and often involves responding to user input and browser events.
5. Standard Library: Node.js comes with a built-in standard library that provides various utility functions, such as networking, file system, and cryptography. JavaScript does not have a built-in standard library but can access a variety of APIs provided by web browsers.

[Q3] What is NPM, and why is it used in Node.js?

NPM (Node Package Manager) is the default package manager for Node.js, which is used for installing and managing third-party packages and dependencies in Node.js projects.

[Q4] What is an event-driven architecture in Node.js?

Event-driven architecture is a programming paradigm where the execution of code is driven by events or triggers.

In Node.js, the event-driven architecture allows developers to handle multiple requests simultaneously without blocking the execution of other code.

[Q5] What is a callback function in Node.js?

A callback function is a function that is passed as an argument to another function, which is then called when the parent function completes its task.

In Node.js, callback functions are used extensively for asynchronous programming.

An example of a callback function is given below:

   function add(a, b, callback) {
     callback(a + b);
   }

   add(2, 3, function(result) {
     console.log(result); // Output: 5
   });

[Q6] What is the difference between asynchronous and synchronous programming in Node.js?

Synchronous programming blocks the execution of code until a particular task is completed, while asynchronous programming allows the code to continue executing while a particular task is being completed in the background.

[Q7] What is the difference between the process.nextTick() and setImmediate() methods in Node.js?

The process.nextTick() method is used to schedule a callback function to be executed in the next iteration of the event loop, while setImmediate() is used to execute a callback function after the current operation is completed, but before the next event loop iteration.

[Q] Explain the difference between setImmediate() and setTimeout() in Node.js.

setImmediate() and setTimeout() are both used to execute a function after a certain delay, but there are some differences:

• setImmediate() queues the function for execution in the current iteration of the event loop, while setTimeout() schedules the function to be executed after the specified delay.
• If you call setImmediate() multiple times within a single event loop iteration, the callbacks will be executed sequentially in the order they were queued. On the other hand, if you call setTimeout() multiple times with the same delay, the order in which the callbacks are executed is not guaranteed.

[Q8] What is a package.json file in Node.js?

The package.json file is a metadata file that describes a Node.js package, including its dependencies, version, and other configuration details.

[Q9] What is the purpose of the ‘require’ function in Node.js?

The ‘require’ function is used to load modules or packages in Node.js. It takes a single argument, which is the name of the module or package to be loaded.

const http = require('http');

[Q] How do you read data from a file using Node.js?

You can read data from a file using the fs module in Node.js. Here is an example of how to read data from a file:

   const fs = require('fs');

   fs.readFile('file.txt', 'utf8', function(err, data) {
     if (err) throw err;
     console.log(data);
   });

[Q10] What is an EventEmitter in Node.js?

An EventEmitter is a class in Node.js that allows objects to emit and handle events.

[Q11] What is the purpose of the ‘fs’ module in Node.js?

The ‘fs’ module is a built-in module in Node.js that provides file system-related functionality, including reading and writing files.

In Node.js, the built-in fs (file system) module provides a way to work with the file system on your computer. It provides methods for reading and writing files, creating and deleting directories, and more. Here’s an example of how to use the fs module to read a file:

const fs = require('fs');

const data = 'hello world';

fs.writeFile('file.txt', data, (err) => {
  if (err) {
    console.error(err);
    return;
  }
  console.log('File has been written');
});

[Q12] What is the purpose of the ‘http’ module in Node.js?

The ‘http’ module is a built-in module in Node.js that provides functionality for creating HTTP servers and clients.

[Q13] How do you create a basic HTTP server in Node.js?

You can create a basic HTTP server in Node.js using the http module. Here is an example of how to create a basic HTTP server:

   const http = require('http');

   const server = http.createServer(function(request, response) {
     response.writeHead(200, {'Content-Type': 'text/plain'});
     response.end('Hello, world!');
   });

   server.listen(8080);

[Q13] What is middleware in Node.js?

A middleware is a function that is executed between the server receiving a request and sending a response. It is used to perform tasks such as logging, authentication, and error handling.

[Q14] What is NPM in Node.js?

NPM (Node Package Manager) is a package manager for Node.js that allows developers to easily install, manage, and publish packages and modules.

[Q ] How do you install and use external packages in Node.js?

You can install external packages in Node.js using the npm package manager.

Here is an example of how to install the express package:

   npm install express

[Q15] What is the purpose of the ‘path’ module in Node.js?

The ‘path’ module is a built-in module in Node.js that provides functionality for working with file and directory paths.

In Node.js, the path module is used to work with file and directory paths.

Here is an example of how to use the path module to create and manipulate file paths: javascript

   const path = require('path');

   // Get the current directory
   const currentDirectory = path.resolve();

   // Join two file paths together
   const filePath = path.join(currentDirectory, 'files', 'example.txt');

   // Get the file extension of a path
   const fileExtension = path.extname(filePath);

   // Print out the results
   console.log('Current directory:', currentDirectory);
   console.log('File path:', filePath);
   console.log('File extension:', fileExtension);

[Q16] What is the purpose of the ‘os’ module in Node.js?

The ‘os’ module is a built-in module in Node.js that provides information about the operating system, including CPU usage, memory usage, and network interfaces.

In Node.js, the os module provides a way to interact with the operating system. It allows you to get information about the current operating system, such as the CPU architecture, total memory, and network interfaces.

Here is an example of how to use the os module

   const os = require('os');

   // Get the operating system's CPU architecture
   const cpuArchitecture = os.arch();

   // Get the operating system's platform
   const platform = os.platform();

   // Get the total memory in bytes
   const totalMemory = os.totalmem();

   // Get the network interfaces
   const networkInterfaces = os.networkInterfaces();

   // Print out the results
   console.log('CPU architecture:', cpuArchitecture);
   console.log('Platform:', platform);
   console.log('Total memory:', totalMemory, 'bytes');
   console.log('Network interfaces:', networkInterfaces);

[Q17] What is a stream in Node.js?

A stream is a collection of data that is transmitted serially, piece by piece, in real time. Streams are used to efficiently process large amounts of data in Node.js.

In Node.js, streams are used to handle reading and writing data from various sources and destinations. Streams are a way to process large amounts of data in chunks, instead of loading all the data into memory at once.

Here is an example of how to use streams in Node.js:

   const fs = require('fs');

   // Create a readable stream
   const readableStream = fs.createReadStream('input.txt', { encoding: 'utf8' });

   // Create a writable stream
   const writableStream = fs.createWriteStream('output.txt', { encoding: 'utf8' });

   // Pipe the data from the readable stream to the writable stream
   readableStream.pipe(writableStream);

   // Handle errors
   readableStream.on('error', (err) => console.log('Error:', err));
   writableStream.on('error', (err) => console.log('Error:', err));

   // Handle the end of the writable stream
   writableStream.on('finish', () => console.log('Data has been written to output.txt'));

[Q18] What is the purpose of the ‘child_process’ module in Node.js?

The ‘child_process’ module is a built-in module in Node.js that provides functionality for creating and managing child processes.

In Node.js, child_process is a built-in module that provides a way to create and interact with child processes (i.e., processes that are spawned from a parent process). This module allows Node.js to execute other programs or scripts in parallel, which can help improve the overall performance and efficiency of a Node.js application.

There are four different ways to create child processes in Node.js using the child_process module:

1. spawn: This method creates a new child process by spawning a command in a new process and providing a streaming interface for I/O.
2. exec: This method creates a new child process by executing a command in a shell and buffers the output.
3. execFile: This method creates a new child process by executing a file with a set of arguments and buffers the output.
4. fork: This method is a variation of spawn that creates a new Node.js process and establishes a communication channel between the parent and child processes.

The child_process the module provides various methods to communicate with the child process, such as stdin, stdout, and stderr. These methods allow the parent process to send input to the child process and receive output from the child process.

[Q19] What is the purpose of the ‘crypto’ module in Node.js?

The ‘crypto’ module is a built-in module in Node.js that provides cryptographic functionality, including hash functions and encryption/decryption.

const crypto = require('crypto');

const data = 'hello world';

// Create a SHA256 hash digest
const hash = crypto.createHash('sha256');
hash.update(data);
const digest = hash.digest('hex');

console.log(digest); // Outputs: 'b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9'

[Q20] What is the purpose of the ‘cluster’ module in Node.js?

The ‘cluster’ module is a built-in module in Node.js that allows Node.js applications to utilize multiple processor cores for increased performance and scalability.

const cluster = require('cluster');
const numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  console.log(`Master ${process.pid} is running`);

  //

[Q] What is the purpose of the exports object in Node.js?

The exports object in Node.js is used to expose functions and objects to other modules. You can assign properties to the exports object to make them available for use in other files.

// math.js
exports.add = function(a, b) {
  return a + b;
}

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

[Q] Write a function to calculate the factorial of a number in Node.js.

function factorial(num) {
  if (num === 0) {
    return 1;
  } else {
    return num * factorial(num - 1);
  }
}

[Q] Write a function to sort an array of numbers using the bubble sort algorithm in Node.js.

function bubbleSort(arr) {
  let n = arr.length;

  for (let i = 0; i < n - 1; i++) {
    for (let j = 0; j < n - i - 1; j++) {
      if (arr[j] > arr[j + 1]) {
        let temp = arr[j];
        arr[j] = arr[j + 1];
        arr[j + 1] = temp;
      }
    }
  }

  return arr;
}

How do you handle errors in Node.js?

In Node.js, you can handle errors using try-catch blocks or by using the error event.

try {
  // some code that may throw an error
} catch (error) {
  // handle the error here
}

// or

someFunction().on('error', (error) => {
  // handle the error here
});

Write a function that returns the sum of two numbers in Node.js.

Below is the function which will return the sum of two numbers in Node Js

function add(a, b) {
  return a + b;
}

How do you read a file in Node.js?

To read a file in Node.Js, You can use the fs module to read a file in Node.js. The fs.readFile() method is an asynchronous method that takes a filename, encoding, and callback function as arguments.

const fs = require('fs');

fs.readFile('file.txt', 'utf8', function(err, data) {
  if (err) throw err;
  console.log(data);
});

[Q] Explain the difference between require() and import in Node.js.

require() is a function used in Node.js to load modules, while import is a feature in ES6 used to load modules.

require() is a synchronous operation, while import is asynchronous.

// Using require()
const math = require('./math');
console.log(math.add(2, 3));

// Using import
import { add } from './math';
console.log(add(2, 3));

[Q] How do you create a server in Node.js?

You can create a server in Node.js using the http module.

const http = require('http');

const server = http.createServer((req, res) => {
  res.write('Hello World!');
  res.end();
});

server.listen(8080, () => {
  console.log('Server listening on port 8080');
});

[Q] What is middleware in Node.js? Explain with code example

Middleware is a function that sits between the request and response in a Node.js application. It can modify the request or response, or perform some other action.

function myMiddleware(req, res, next) {
  // do something here
  next();
}

app.use(myMiddleware);

How do you handle cookies in Node.js?

You can use the cookie-parser middleware to handle cookies in Node.js. This middleware parses the Cookie header and populates req.cookies with an object keyed by the cookie names.

const cookieParser = require('cookie-parser');

app.use(cookieParser());

app.get('/', (req, res) => {
  const cookieValue = req.cookies.myCookie || 'default';
  res.cookie('myCookie', 'value');
  res.send(`Cookie value: ${cookieValue}`);
});

[Q] How do you connect to a MongoDB database in Node.js?

To connect with MongoDB database we will need to use MongoDB package and methods.

const MongoClient = require('mongodb').MongoClient;

MongoClient.connect('mongodb://localhost:27017/mydb', function(err, client) {
  if (err) throw err;
  const db = client.db('mydb');
  // do something with the database
  client.close();
});

How do you use clustering in Node.js?

Clustering in Node.js is used to distribute the load across multiple CPU cores. You can use the cluster module to create a cluster of worker processes.

const cluster = require('cluster');
const numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }
} else {
  // do something in the worker process
}

How do you use streams in Node.js?

Streams in Node.js are used to process large amounts of data in chunks. They can be used to read data from a file or a network socket, and to write data to a file or a network socket.

Here’s an example of how to use streams in Node.js:

const fs = require('fs');

const readableStream = fs.createReadStream('input.txt');
const writableStream = fs.createWriteStream('output.txt');

readableStream.pipe(writableStream);