Top 20 Node.js Interview Questions and Answers

With the boosting popularity of JavaScript, the world has seen a revolutionary change in web development. The process and techniques of web designing have taken a dramatic turn. JavaScript running on the server and in the browser has opened new possibilities and helped us discover ways we weren’t aware of. Here We cover Top 20 Node.js interview questions and answers for developers

1. What is node.js? How node.js works?

Node.js is an open-source, cross-platform runtime environment for developing server-side and networking applications written in JavaScript. It is the archetype of an exceedingly customizable and scalable tech. JS is designed to use single-threaded, event-based architecture and non-blocking-based I/O models. It is made of Google Chrome’s V8 engine written in multiple-platform C library i.e C++ and Libuv that backs asynchronous I/O based events on event loops and thread loops. Although Node.js is made of Libuv, it can still be used in pure JavaScript.

2. Where can we use node.js?

Node.js can be used at a variety of platforms. Some examples are stated below:

  • Backend for Social Media Networking – LinkedIn
  • Single-page Application – GitHub
  • Chat Application –
  • Data Streaming – Netflix
  • IoT Application – PREE

3. What is the advantage of using node.js?

Node.js is used by professionals and some extremely renowned companies like Netflix and Uber. Evidently, it possesses features that make it the best. Below mentioned are some advantages of using Node.js

  • Easy to learn because of its accessibility and object-oriented programming.
  • Simple to use because it only uses one language as the catalyst of the full-stack development.
  • It is Faster to deploy, as programs and websites built with Node.js require less time on development hence reducing the overall time-to-market.
  • Node.js is a scalable alternative to Apache. It can handle various concurrent connections and distribute tasks skillfully amongst resources.

Check Out What It Takes To Build A Successful App Here

4. What are the two types of API functions in Node.js?

Node.js has two types of API functions

  • Asynchronous, Non-blocking functions
  • Synchronous, Blocking functions

5. What is control flow function? Explain the steps how “Control Flow” controls the functions calls?

The order in which the execution of statements is done by the computer is called Control Flow. The control flow function in Node.js is a code that is applied between Asynchronous function calls. Below given are steps which are used to implement Control Flow Function.

  • Execution order must be controlled
  • Collect the required data
  • Concurrency must be limited
  • After this, the program is requested

6. Why is Node.js quickly gaining attention from JAVA programmers?

The reason behind Node.js rapidly gaining popularity is its loop-based server for JavaScript. Node.js provides the developer the facility to write JavaScript on the server.

7. What is the event loop in Node.js work? And how does it work?

The I/O non-blocking operation of Node.js is made possible through event loops despite JavaScript is a single-threaded language. At the beginning of the process, Node.js initialises the event loop, processes the provided input script that syncs API calls, schedule timers, then starts processing the event loops.

8. How will you debug an application in Node.js?

Debugging means relieving your code from any error. Identifying an error can take up many hours for which Node.js has a great tool that can help finding the error.

Open the initial file (typically index.js), activate the Run and Debug pane, and click the Run and Debug Node.js (F5) button. The debugging screen is similar to Chrome DevTools with a Variables, Watch, Call stack, Loaded scripts, and Breakpoints list.

9. What are some of the most popular modules of Node.js?

Every developer must be equipped with the latest information and updates on software libraries as they make the task of programming very easy. The most popular and useful modules of Node.js are-

  • Express
  • Body-parser
  • Cora
  • Passport
  • Multer

10. What is a Callback function in Node.js?

Callback function is employed when a task is complete. Hence it is a precaution against any kind of blocking. In the meantime, the callback function allows other codes to run. With the Callback function, Node.js becomes immensely scalable as it can process a large amount of requests without waiting for any function to return the results.

11. What are the challenges with Node.js?

Even though Node.js is one of the most popular and widely used open sources software, it has its own challenges-

  • The performance of Node.js is restricted by the heavy computation tasks and also till date Node.js cannot process CPU bound tasks.
  • There might be Callback issues because of their asynchronous nature.
  • Despite having stable modules, Node.js still has immaturity within tools. There are several tools in the npm registry that aren’t structured well enough.

We Built An App That Streamlining the Accreditation Process for Physicians

12. What is REPL in Node.js?

REPL stands for Read-Eval-Print-Loop. This is a virtual environment that comes with Node.js. It is a quick and easy way to test simple Node.js codes.

13. What is a test pyramid in Node.js?

A test pyramid is a metaphor that is used to make a bunch of software tests of different granularity. For example, unit testing, component testing, integration testing, system testing, end-to-end testing, UI testing.

14. Explain the concept of middleware in Node.js.

Middleware is a function that has the access to the requested object, requested response and the next function in the application’s request-response cycle. The middleware function can perform multiple tasks such as; execute code, make changes to the request and the response objects, end the request-response cycle and call the next middleware in the stack.

15. Describe Node.js exit codes.

Exit codes in Node.js are particular codes which help in finishing the processes. This may also include global objects. Some examples of exit code in Node.js are-

  • Internal JavaScript Evaluation Failure
  • Fatal Error
  • Internal Exception
  • Handler Run-time failure
  • Unused
  • Uncaught fatal exception

16. Differentiate between Node.js vs Ajax?

The major difference between Nodes.js and Ajax is –

Nodes.js is a server-side platform for developing client-server applications, whereas Ajax is a client-side scripting technique that was basically designed to show the contents of a page without refreshing it.

17. What are the security mechanisms available in Node.js?

Node.js is equipped with various security mechanism, some are mentioned below:

  • Certified Security Modules can assess any third part codes that are catered into the software.
  • Regular updates of versions are made in Node.js so that it does not become vulnerable to hackers.
  • Curated Screening Register is a kind of quality control system through which every new package code or software is passed to maintain safety before downloading.

18. What are some of the flags used in the read/write operations in files?

Node.js uses several flags in the read/write operations in files. Below mentioned are some of the flags:

  • r : open file for reading
  • r+ : open file for reading and writing
  • rs : Open file for reading in synchronous mode
  • w : Open file for writing
  • a : Open file for appending

19. What is the difference between fork() and spawn() methods in Node.js?

Spawn command is designed to run system commands. When Spawn command is used, you send it a system command that is processed on its own but no further code is processed within your node process. Whereas, Fork is a special instance of Spawn. This means that you can create workers for running the exact same Node code base or maybe a different module for a particular task.

20. What do you understand by an Event Emitter in Node.js?

Node.js is created with a feature of conducting custom events by using event modules. These event modules include an EventEmitter class that is used to raise and operate custom events. Some important methods of EventEmitter class are:

  • emitter.addListener(event, listener)
  • emitter.on(event, listener)
  • emitter.once(event, listener)
  • emitter.removeListener(event, listener)
  • emitter.remove all listeners([event])

Frequently Asked Questions

What are the advantages of using Node.js?

Node.js is JavaScript-based. JavaScript is one of the most popular and simplest coding languages in the IT world. It is easy to learn for beginning developers. Even people without the knowledge of JavaScript but with some basic technical background can read and understand the code.

More than that, the pool of JavaScript talents is large, so as a business owner, you have full freedom to choose the team to work with.

How do I hire a NodeJS developer from Mindbowser?

Get expert Node developers on a full-time or hourly basis (dedicated monthly) to create feature-rich, dynamic, and secure web apps in 4 simple step. Our remote NodeJS developers have experience building complex enterprise-grade Node.js web apps for small to large scale companies.

Why should I outsource my NodeJS development to Mindbowser?

Mindbowser is a company of choice for 400+ companies looking to bring transformation with technology. Our vision is to help build 100+ companies with 10M+ USD valuation and we are already successful in it. Currently, we have 11 companies in our portfolio that have gone beyond 10M+ in valuation. This aligns with our mission to always work on contributing needle-moving changes for you. Our customers have been featured on ProductHunt, TechCrunch, Discovery Channel, Cosmopolitan Magazine,, etc, and have had successful exits. Our clients have also received millions of dollars in funding from marquee investors like the Chan Zuckerberg initiative, Simons Foundation, The Carson family charitable trust, and many more.

What kind of performance guarantees are in place?

We have SLAs defined for projects. This includes performance parameters for individuals as well as key goals for the overall project. We keep revisiting this SLA at regular intervals to make sure that we are inline with the plan. Any deviation is immediately fixed.



In this article we covered the top 20 Node.js  interview questions and answers for freshers. If you have any doubts regarding this article, Please comment us.

Hire the Expert Node.js Developers to Build an Exceptional Solutions to Help Your Web Application Succeed.

Content Team

This blog is from Mindbowser‘s content team – a group of individuals coming together to create pieces that you may like. If you have feedback, please drop us a message on

Get in touch for a detailed discussion.

Hear From Our 100+ Customers

Mindbowser helped us build an awesome iOS app to bring balance to people’s lives.


We had very close go live timeline and MindBowser team got us live a month before.

Shaz Khan
CEO, BuyNow WorldWide

They were a very responsive team! Extremely easy to communicate and work with!

Kristen M.
Founder & CEO, TotTech

We’ve had very little-to-no hiccups at all—it’s been a really pleasurable experience.

Chacko Thomas
Co-Founder, TEAM8s

Mindbowser is one of the reasons that our app is successful. These guys have been a great team.

Dave Dubier
Founder & CEO, MangoMirror

Mindbowser was very helpful with explaining the development process and started quickly on the project.

Hieu Le
Executive Director of Product Development, Innovation Lab

The greatest benefit we got from Mindbowser is the expertise. Their team has developed apps in all different industries with all types of social proofs.

Alex Gobel
Co-Founder, Vesica

Mindbowser is professional, efficient and thorough. 

MacKenzie R
Consultant at XPRIZE

Very committed, they create beautiful apps and are very benevolent. They have brilliant Ideas.

Laurie Mastrogiani
Founder, S.T.A.R.S of Wellness

MindBowser was great; they listened to us a lot and helped us hone in on the actual idea of the app.” “They had put together fantastic wireframes for us.

Bennet Gillogly
Co-Founder, Flat Earth

They're very tech-savvy, yet humble.

Uma Nidmarty
CEO, GS Advisorate, Inc.

Ayush was responsive and paired me with the best team member possible, to complete my complex vision and project. Could not be happier.

Katie Taylor
Founder, Child Life On Call

As a founder of a budding start-up, it has been a great experience working with Mindbower Inc under Ayush's leadership for our online digital platform design and development activity.

Radhika Kotwal
Founder of Courtyardly

The team from Mindbowser stayed on task, asked the right questions, and completed the required tasks in a timely fashion! Strong work team!

Michael Wright
Chief Executive Officer, SDOH2Health LLC

They are focused, patient and; they are innovative. Please give them a shot if you are looking for someone to partner with, you can go along with Mindbowser.

David Cain
CEO, thirty2give

We are a small non-profit on a budget and they were able to deliver their work at our prescribed budgets. Their team always met their objectives and I'm very happy with the end result. Thank you, Mindbowser team!!

Bart Mendel
Founder, Mindworks

Mindbowser was easy to work with and hit the ground running, immediately feeling like part of our team.

George Hodulik
CEO, Stealth Startup, Ex-Google