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.

Q1. Why is Node.js single-threaded?

It was created especially as an examination in async processing. The hypothesis was that performing async processing on to a single thread could give more execution and adaptability under average web loads than the common thread-based usage.

Q2. How is observable different from promise?
Observables Promises
These are used for streams of events over time. It is able to handle only one event.
It supports operators such as map, filter, reduces, etc., and is cancel-able and retry-able. It is not easy to handle and returns a single value.
It provides chaining and subscriptions for handling complex applications. It uses only the .then() clause.
Here the subscribe method is used for a centralized and predictable error handling. It pushes the errors to the child's promises.

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

Q3. What is an Event Loop?

The event loop is the thing that allows Node.js to operate the non-blocking input/output operations. Despite the originality, JavaScript is a single-threaded that is used for offloading the operations to the kernel of the system, when possible.

Event Loop
It allows Node JS to perform non-blocking I/O operations despite the fact. In Node.js codes runs on a single thread.

Phases of the Event loop

  • Timers
  • Pending Callbacks
  • Idle, Prepare
  • Poll
  • Check
  • Close Callbacks
Phases of Event Loop

console.log("This is first title");
    console.log("This is second title");
}, 1000);
console.log("This is third title");


This is first title

This is third title

This is second title


Q4. Why are promises better than callbacks?

Here are some of the reasons why promises are better than callbacks:

  • They are built over callbacks and very efficient abstractions.
  • They allow cleaner and better functional code.
  • They end up with fewer error-prone boilerplate.
  • They provide a catching mechanism that is not available in Callbacks.
  • You have a superior level of control and trust while delegating tasks through promises rather than callbacks.
Q5. What are the different HTTP methods in Node.js?

There are three HTTP methods in NodeJS. They are:

  • http.createServer(): This is used to create a new instance of the http.server class.
  • http.request(): This is used for making an HTTP request to the server by creating an instance of the http.ClientRequest class.
  • http.get(): It is very much similar to the http.request() method, but it automatically sets the HTTP method to GET and calls the req.end().
Q6. How will you debug an application in Node.js?

The easiest way to debug an application on Node.js is through Node-Inspector. You can use it from any browser supporting WebSockets. It helps multiple ways of debugging like a profiler, livecoding, breakpoints, etc. Here's how to use node-inspector:

  • Install it using npm install -g node-inspector
  • Now, run node-debug app.js
Q7. How to get a user's IP address in node js?

You can use req.connection.remoteAddress to a user's IP address in node js.

Q8. What is chaining in Node.js?

This is a mechanism by which the output of one stream is connected to the output of another stream y creating a long chain of multiple stream operations.

Q9. What do you understand by middleware? How can you use middleware in Node JS?

Middleware functions are those functions having access to the request object (req), the response object (res), and also the next function in an application's request-response cycle. The following function is basically a function in the Express router, when invoked, executes the middleware which is succeeding in the current middleware.

Middlewares can perform the following tasks:
  • Execute any type of code
  • Making changes to the request and response objects
  • We are ending the request-response cycle.
  • Cleaning the next middleware in the stack
Q10. How we can secure HTTP cookies against XSS attacks?

we have to set flags on the set-cookie HTTP header:

  • HttpOnly
  • secure

After this it will lokk like this : Set-Cookie: sid=; HttpOnly

Point to be noted: Make sure that you go through this twice as this is the favorite node js interview questions for fresher and experienced as well.

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...