Node.js Interview Questions and Answers

Last updated on Apr 07, 2023
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Node js Interview Questions

In this world full of development firms we all know how useful Server Side Scripting is. Node.JS is also server-side scripting with the help of which you can build anything, starting from a single program to a complex web application. And that’s why Certified Node.JS developers are in too high demand. Node.JS opens many opportunities for you and to grab you those opportunities we have compiled a popular list of Node.JS Interview Questions and Answers. These questions will also help you to clear all your basic concepts of Node.JS.

It is a web application framework that is built on Google Chrome Javascript’s Engine that compiles JavaScript into machine code and reduces development costs by 58%. This backend framework has been worldwide accepted and can be used in real-time web applications, network applications, single-page applications, etc. In the year 2018, this framework hits 1 billion downloads and you will be surprised to know that Node js powers over 30 million sites out of which 6.3 million sites are from the U.S alone. Developers who are looking for a change and want to give their career a boost, we assure you this list of interview questions surely uplift your confidence.

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Most Frequently Asked Node.js Interview Questions

Here in this article, we will be listing frequently asked Node js Interview Questions and Answers with the belief that they will be helpful for you to gain higher marks. Also, to let you know that this article has been written under the guidance of industry professionals and covered all the current competencies.

Q11. How do you update NPM to a new version in Node.js?

$ sudo npm install npm -g
/usr/bin/npm -> /usr/lib/node_modules/npm/bin/npm-cli.js
[email protected] /usr/lib/node_modules/npm

Q12. What is a buffer and stream in Node.js?


It is a global class that can be accessed in an application without importing the buffer module. It can be constructed in a variety of ways like var buf = new Buffer(5);

Use of a buffer in Node JS

Buffer is used to dealing with TCP streams, reading, and writing data to the filesystem in the Node.js server, which are purely binary teams of data.

It is designed in a way that is easy to manage, faster and has an API designed for binary data, which makes it the perfect choice for handling streams of data.


these are the objects that allow the developers to read the data from the source or can write the data to the destination in an endless manner. They usually have problems with the large data. With a stream, there is no need to wait for the whole resource to load.

There are different types of Stream:

  • Readable
  • Writable
  • Duplex
  • Transfer
Q13. What is Piping in Node JS?

A pipe is a function that reads the data from a readable stream once it is available and writes it in the destination writable stream. It performs all the reasonable things including the errors, files in case any one side falls apart. In due case, piping redirections any readable stream to a writable stream.

Q14. How we can open a file in Node JS?

open() function is used to opens a file by passing a file name.

Syntax :, flags[mode], callback)


  • path : It is a string having file name with complete path
  • flags : It indicates the behavior of the file to be opened
  • mode : It sets the file mode like permission
  • callback : gets two arguments (err, fd)

var fs = require("fs");

// Asynchronous - Open a File
console.log("open file");'file.txt', 'r+', function(err, fd) {
   if (err) {
      return console.error(err);
   console.log("File opened");     

Q15. What are the difference between setTimeout() and clearTimeout()?

setTimeout() : It can be used to schedule code execution after a designated amount of milliseconds.

function myFunc(arg) {
  console.log(`arg was => ${arg}`);
setTimeout(myFunc, 1500, 'funky');

clearTimeout()  :  It can be used to cancel timeout which are set by setTimeout().

console.log('before immediate');
setImmediate((arg) => {
   console.log(`executing immediate: ${arg}`);
}, 'so immediate');
console.log('after immediate');

Q16. What is the timing features of Node.js? Explain some Timers modules?

The timing feature of node.js contains all the necessary functions that are required to execute code after any specific period. As it is built on the V8 JavaScript engine of Google Chrome, hence its library permits the fast execution of code. Timers also provide a number of ways for managing schedules. They don't need to be imported as all the methods are easily available for the browser.

Some modules are –
  • setTimeout
  • setInterval
  • setImmediate
  • clearImmediate(immediate)
  • clearTimeout(timeout)
Q17. Define an error-first callback?

Error-first callbacks are generally used to pass errors as well as data. It is important to pass the error as the first parameter, and then you must check if something went wrong. There are additional arguments that are used to pass data.

Q18. What is a Reactor Pattern in Node.js?

Reactor Pattern is used for non-blocking Input/Output operations in the Node.js. This pattern provides a handler that is associated with I/O operations. When I/O requests are generated, they get submitted to a demultiplexer, which handles concurrency in non-blocking I/O mode and collects requests in the form of an event and queues the events.

Note: This Node js interview questions have been created by Node.js Experts. It shall help you to answer some of the most frequently asked questions during a job interview.

Q19. List some events that fired by streams in Node JS?
  • newListener
  • removeListener
  • EventEmitter: 'removeListener'
  • EventEmitter. listenerCount (emitter, eventName)
  • EventEmitter.defaultMaxListeners
  • emitter.addListener(eventName,listener)
  • emitter.emit(eventName[,...args])
Q20. What is test pyramid? Explain with an example?

A test pyramid is a metaphor that helps the grouping of software tests in a bunch of different granularity. Unit testing pyramid number of tests gets easily fitted.

For instance, unit testing, component testing, integration testing, system testing, end-to-end testing, UI testing, and others. The primary example of it is creating a unit test which will be the fastest and reliable.

node interview questions

Top 20 Node.js Interview Questions

  • Is Nodejs asynchronous?
  • What are the advantages and disadvantages of node JS?
  • What is Closure in Node.js?
  • What are authentication and authorization in node JS?
  • What is Event Loop?
  • Explain Synchronous vs Asynchronous Javascript?
  • Why node is faster than other programming languages?
  • Why we used async & await in Node.js?
  • What are the promises and how do they work?
  • Why is Node.js single-threaded?
  • What is buffer and stream in Node.js?
  • What is callback hell and how can it be avoided?
  • What is Express?
  • What is Middleware?
  • What do you mean by REST API?
  • Why is Node.js so popular for REST API?
  • How do you authenticate API in node JS?
  • What are blocking and non-blocking in Node.js?
  • Why is a node called a non-blocking model?
  • What is Closure?
Quick Facts About Node.js
What is the latest version of Node.js? 15.14 / 15th January 2021.
When was Node.js first released? 27th May 2009
Who is the Author of Node JS? Ryan Dahl
What language is used in Node JS? C, C++, JavaScript
Node.js License MIT License
Operating system Windows, SmartOS, Linux, macOS, Microsoft, FreeBSD, OpenBSD

Being a developer we know that Node.JS is a very vast topic that includes questions of all levels like Fresher, Intermediate, and Advanced level. Reading all questions just before one day of your interview wouldn’t make any sense and that results in more nervousness. This area requires a lot of constant practice and practical experience.

After practicing different questions, try to solve sample papers and some Node MCQ from different websites which will tell you your current progress and area that still requires improvement.

Reviewed and verified by Umesh Singh
Umesh Singh

My name is Umesh Singh having 11+ experience in Node.JS, React JS, Angular JS, Next JS, PHP, Laravel, WordPress, MySQL, Oracle, JavaScript, HTML and CSS etc. I have worked on around 30+ projects. I lo...