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.

Q51. Are promises better than callbacks?

With the help of Promises, Handling error across numerous asynchronous calls has become more effortless in comparison to what it was at the time of using callbacks. Also, having the privilege to not provide any callbacks makes the coding look even cleaner. On the contrary, callbacks present the mechanism of control flow. And they only inform the users about how the application flows, and not really the information of what it does.

Q52. How do you secure an API in Node.js?

The paper “The Protection of Information in Computer Systems” by Jerome Saltzer and Michael Schroeder, cited some 8 principles with the help of which information within the computer systems can be stored efficiently. These are mentioned below :

  • Least Privilege
  • Fail-Safe Defaults
  • Mechanism Economy
  • Complete Meditation
  • Open Design
  • Privilege Separation
  • Least used Mechanism
  • Psychological Acceptability
Q53. Why we use Bodyparser in node JS?

It extracts the complete body portion owned by the stream of the incoming requests and exposes this extraction on the “req.body like something that is easier to interact with. This renders the user the middleware that uses the nodeJS or the zlib for unzipping the incoming data of request if it is zipped plus stream-utils or the raw-body in order to anticipate the full and raw contents belonging to the body of the request before "parsing it".

Q54. Which is more secure SOAP or REST?

The point of differences mentioned below will help you to understand which one is more secure and when:

  • If standardization and security are the main goals, then SOAP should be considered as the stronger one to practice as the Web Services. Also, SOAP offers WS-Security which is like an extra perk to the enterprise.
  • The REST API is compatible with a number of types of data outputs including JSON, XML, CSV while SOAP is able to handle XML only. With the help of REST using JSON helps to cut down a lot on the expenses.
  • REST is further advanced, therefore when the next endpoint requests one query completed beforehand, the development of API can make use of the data that too from the earlier request. Whereas, SOAP implementations need to process all the queries each and every single time.

Although it sounds as if SOAP is more advantageous than REST, yet one good REST implementation can be really beneficial for an enterprise rather than using the poorly-designed SOAP API. And SOAP possesses in-built error handing to communicate errors through the specification of WS-ReliableMessaging. Whereas, REST needs to send the transfer again every time it encounters one error.

Q55. How do you write a callback function in node JS?

A callback function is an asynchronous equivalent for a function. It's called at the completion of each and every task. In Node.js, callbacks are generally used, and all the APIs of Node are written in a way to support callback functions.

When a function starts reading a file, it returns the control to the execution environment immediately so that the next request can be executed, and this is a perfect example of a callback function.


Here’s how to write a callback function in Node.js:

var myCallback = function(data) {
  console.log('got data: '+data);

var usingItNow = function(callback) {
  callback('get it?');

Q56. What is spawn in Node JS?

The spawn is a method in NodeJS that spawns an external application through a new process and finally returns a streaming interface for I/O. It is excellent for handling applications that produce a large amount of data or for working with streams of data as it reads in.


Here’s an example how child process have the ability to use the spawn method:

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

ls.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);

ls.stderr.on('data', (data) => {
  console.error(`stderr: ${data}`);

ls.on('close', (code) => {
  console.log(`child process exited with code ${code}`);

Q57. What are the pros and cons of using promises instead of callbacks?
Here are the pros of using promises over callbacks:
  • Better defined and organized control flow of asynchronous logic.
  • Highly reduced coupling.
  • We have integrated error handling.
  • Enhanced readability.
Cons of using Promises over callbacks:
  • It kills the purpose of asynchronous non-blocking I/O.
  • Only one object can be returned.
  • We cannot return multiple arguments.
Q58. What is Node.js and why it is used?

Node.js, as open-source server environment, runs on various platforms such as Windows, Unix, Linux, etc. The anchor of the MEAN stack, Node.js is also one of the most popular server platforms in the world.

Why it is used?
  • It is asynchronously programming, runs single-threaded, non-blocking which is very memory efficient.
  • It can operate file various operations like create, open, write, read, delete, and close files on the server and can collect form data.
Q59. What are the advantages of Node JS?
  • Scalable and extensible
  • Easy to learn
  • Used as a Single Programming Language
  • Offers benefits of Fullstack JS
  • Offers High Performance
Q60. Why we used NPM in Node js?

The NPM provides two main functionalities:

  • It is the online repository for all of the Node.js packages.
  • It is the command line utility for installing, version management and dependency management of the Node.js packages.

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...