25 Most Asked: Node.js Interview Questions


As famously quoted by Ryan Dahl, the creator of Node.js

“You can never understand everything. But you should push yourself to understand the System.”
And to understand a system, practice and patience are the prerequisites. 

Even after finishing the course material and projects, sometimes it becomes difficult to articulate your answers during the course of an interview. It helps to know important questions and prepare them in advance. 

In this blog, we are going to cover Node.js questions which will help you sail through your interviews. 

It has gained immense popularity as a server-side platform. It allows developers to use JavaScript to write command line tools and for server-side scripting, which produces dynamic web page content before the page is sent to the user’s web browser. It represents the java script everywhere paradigm, scripting for both the client side and server side. 

If you are looking for a career in tech and specifically software and web development you might want to be thorough with your JavaScript and Node.js concepts. 

The biggest names in the business, be it Netflix, PayPal, or Linkedin, all have used this technology to develop their super fast, superior quality applications.

These questions will help you prepare for your interview better.

1. What is Node.js?

It is an open-source server-side runtime environment built on Chrome’s V8 JavaScript engine. While being a cross-platform runtime environment and library it is used for running web applications outside the client’s browser.

The main characteristics of are:

  • Is based on the JavaScript programming language
  • Uses a single-threaded event loop
  • Event-driven, non-blocking I/O strategy to enable excellent speed and application scalability
  • An application’s front-end and back-end may be written in the same language
  • MongoDB and Express.js, are often used in applications

2. What are the benefits of using Node.js?

  • It helps optimize both throughput and scalability in web applications
  • The code is written in JavaScript resulting in less time spent in “context shift” between languages for both client and server-side 
  • The NPM (Node Package Manager) provides access to thousands of reusable package
  • It also has best-in-class dependency resolution
  • Can also be used to automate most of the build toolchain
  • It is portable and is well-supported by many web hosting providers
  • With an active third-party ecosystem and developer community, finding relevant resources and help is easier

3. Explain the working of Node.js?

It is a Platform doesn’t follow the Multi-Threaded Request/Response Stateless Model. It follows the Single-Threaded with Event Loop Model. NPM mainly inspired by JavaScript Event-based model with JavaScript callback mechanism. Because of this Node.js can handle more concurrent client requests with ease. The event loop is the heart of the NPM.

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

The two types of API functions in Node.js :

  • Asynchronous, non-blocking functions
  • Synchronous, blocking functions

5. What do you mean by asynchronous API?

All APIs of the Node.js library is asynchronous and non-blocking. It essentially means a Node.js based server never waits for an API to return data. The server moves to the next API after calling it and a notification mechanism of Events of Node.js helps the server to get a response from the previous API call.

6. Explain Node.js web application architecture?

A web application distinguishes into 4 layers:

  • Client Layer: The Client layer contains web browsers, mobile browsers, or applications that can make an HTTP request to the web server.
  • Server Layer: The Server layer contains the Web server which can intercept the request made by clients and pass them the response.
  • Business Layer: The business layer contains an application server that is utilized by the web server to do required processing. This layer interacts with the data layer via a database or some external programs.
  • Data Layer: The Data layer contains databases or any source of data

7. Why is Node.js single-threaded?

For async processing, Node.js was created explicitly as an experiment. It is believed that more performance and scalability can be achieved by doing async processing on a single thread under typical web loads than the typical thread-based implementation.

8. What is an event loop in Node.js?

To process and handle external events and convert them into callback invocations an event loop is used. So, at I/O calls, it can switch from one request to another

9. Mention the steps by which you can async in Node.js?

By following steps you can async it:

  • First class functions
  • Function composition
  • Callback Counters
  • Event loops

10 How is Node.js most frequently used

It is widely used in the following applications:

  1. Real-time chats
  2. Internet of Things
  3. Complex SPAs (Single-Page Applications)
  4. Real-time collaboration tools
  5. Streaming applications
  6. Microservices architecture

11. What do you understand by the term I/O?

The term I/O stands for input and output. It is used to access anything outside of your application. The I/O describes any program, operation, or device that transfers data to or from a medium or another medium. This medium can be a physical device, network, or files within a system.

I/O is loaded into the machine memory to run the program once the application starts.

12. Is it free to use Node.js?

Yes, it is registered under the MIT license and is free to use. 

13. What are the pros and cons of Node.js?


  • If your application does not have any CPU intensive computation, you can build it in Javascript top to bottom, even down to the database level if you use JSON storage object DB like MongoDB.
  • Crawlers receive a full-rendered HTML response, which is far more SEO friendly rather than a single page application or a websockets app run on top of it.


  • Any intensive CPU computation will block it’s responsiveness, so a threaded platform is a better approach.
  • Using relational databases with Node.js is considered less favorable.

14. What is the difference between Node.js vs Ajax?

The difference between Node.js and Ajax is that Ajax (short for Asynchronous Javascript and XML) is a client side technology, often used for updating the contents of the page without refreshing it. Node.js is Server Side Javascript, used for developing server software. Node.js does not execute in the browser but by the server.

15. What does “non-blocking” mean in Node.js?

In Node.js “non-blocking” means that its IO is non-blocking. It uses “libuv” to handle its IO in a platform-agnostic way. On windows, it uses completion ports for unix it uses epoll or kqueue etc. So, it makes a non-blocking request and upon a request, it queues it within the event loop which calls the JavaScript ‘callback’ on the main JavaScript thread.

16. What is the purpose of Buffer class in Node?

Buffer class is a global class and can be accessed in application without importing the buffer module. A Buffer is a kind of an array of integers and corresponds to a raw memory allocation outside the V8 heap. A Buffer cannot be resized.

17. Mention the framework most commonly used in Node.js?

The most common framework used is “Express”.

18. What is ‘Callback’ in Node.js?

Callback function is used to deal with multiple requests made to the server. Like if you have a large file which is going to take a long time for a server to read and if you don’t want a server to get engaged in reading that large file while dealing with other requests, a call back function is used. Call back function allows the server to deal with pending requests first and call a function when it is finished.

19. How are Node.js and Java Script different from each other?

Java ScriptNode.js
Java Script is a programming language used for writing scripts on the website.It is an interpreter and run time environment for JavaScript
JavaScript is used for any client-side activity for a web application.It is used for accessing or performing any non-blocking operation of any operating system.
The running engine for JavaScript is Spider monkey (Firefox), JavaScript Core (Safari), V8 (Google Chrome), etc.The running engine for Node.js is V8 (Google Chrome).
JavaScript can only be run in browsers.The Node.js code can be run outside the browser.
JavaScript is basically used on the client-side and is used in frontend development.It is mostly used on the server-side and is used in server-side development.
JavaScript is capable enough to add HTML and play with the DOM.It is not compatible enough to add HTML tags.
Some examples of the JavaScript frameworks are RamdaJS, TypedJS, etc.Some examples of the modules are Lodash, express, etc. We have to import these modules from npm.
JavaScript is the upgraded version of ECMA script that uses Chrome’s V8 engine and is written in C++.It is written in C, C++, and Javascript.

20. How can you manage the packages in your Node.js project?

We can manage the packages in our project by using several package installers and their configuration file accordingly. Most of them use npm or yarn. The npm and yarn both provide almost all libraries of JavaScript with extended features of controlling environment-specific configurations. We can use package.json and package-lock.json to maintain versions of libs being installed in a project. So, there is no issue in porting that app to a different environment.

21. What is NPM?

NPM stands for Node Package Manager, responsible for managing all the packages and modules

It provides two main functionalities:

  • Provides online repositories for node.js packages/modules, which are searchable on search.nodejs.org
  • Provides command-line utility to install Node.js packages and also manages versions and dependencies  

22. Why is Node.js preferred over other backend technologies like Java and PHP?

Some of the reasons why it is preferred include:

  • It is very fast
  • Node Package Manager has over 50,000 bundles available at the developer’s disposal
  • Perfect for data-intensive, real-time web applications, as Node.js never waits for an API to return data
  • Better synchronization of code between server and client due to same code base
  • Easy for web developers to start using Node.js in their projects as it is a JavaScript library

23.  What do you understand about callback hell in Node.js?

Callback hell is a phenomenon that creates a lot of problems for a JavaScript developer when he tries to execute multiple asynchronous operations one after the other. A function is called an asynchronous function when some external activity must complete before processing a result. It is called asynchronous because there is an unpredictable amount of time before a result becomes available. These functions require a callback function to handle errors and process the result.


  1. getData(function(a){  
  2.     getMoreData(a, function(b){  
  3.         getMoreData(b, function(c){   
  4.             getMoreData(c, function(d){   
  5.                 getMoreData(d, function(e){   
  6.                     …  
  7.                 });  
  8.             });  
  9.         });  
  10.     });  
  11. });  

24. Mention the steps by which you can async in Node.js?

By following steps you can async:

  • First class functions
  • Function composition
  • Callback Counters
  • Event loops

25.  What are some commonly used timing features of Node.js

Following is a list of some commonly used timing features:

  • setTimeout/clearTimeout: This timing feature of Node.js is used to implement delays in the code execution.
  • setInterval/clearInterval: The setInterval or clearInterval timing feature is used to run a code block multiple times in the application.
  • setImmediate/clearImmediate: This timing feature is used to set the execution of the code at the end of the event loop cycle.
  • nextTick: This timing feature sets the execution of code at the beginning of the next event loop cycle.

You may find these questions repeated across websites and blogs and they are cited and explained frequently because of their importance. With this exhaustive list, we wish you the best in your interview preparation.

Join our Advanced Backend Development boot camp and crack a high-paying tech job in just 4 months

We help you break the glass ceiling which blocks entry to tech. We are a team of IIT / ISB alumni who are passionate about solving the key problem of starting a career in tech. A lot of smart and handworking graduates find it difficult to crack high paying tech jobs either because of their background and their college not being able to help them get interviews. Hence, we started this placement bootcamp that hand holds people from skilling till employment.

Leave a Reply

Your email address will not be published. Required fields are marked *