Node JS Interview Questions

Node JS Interview Questions | Freshers & Experienced

  • Ketan Chauhan
  • 04th Dec, 2021

About Node Js

Node.js is a kind of open-source platform which is used for executing JavaScript by using the various codes prepared using the Java programming language outsides any of the browsers used. It provides a kind of cross-section between the various source codes and helps in the run time built up of the platform.

Finally, Practice here best Nodejs Interview Questions & Answers for the best preparation for the Node.js Interview. These Node.js Interview Questions are very popular and asked various times in Node.js Interview & Placement drives.

Key Features of Node Js

Below are few major features of Node Js

Asynchronous and Event-Driven

Very Fast

Highly Scalable

Massive Speed Gains



Synchronous Code Executions

Practice Best Node JS Interview Questions & Answers

Q1. What is Node.js?

Node.js is an open-source, server-side Javascript runtime platform that is built on Google Chrome's V8 Javascript Engine. Node.js is developed by Ryan Dahl and written in C, C++, JavaScript programming language.


Q2. What is let, const and var in Node JS?

let, const and var in Node JS

Var – a variable declared with var can be used in the entire program. It is declared as the variable is available to access within that function. Also, the variable can be updated anytime.

Let – Let is considered to be a block with curly brackets. A variable with let and curly brackets (block), means that the variable can be used only within the specified block.

Const – Variables that do not need to get updated in the complete lifecycle of the program are declared with const.

Q3. What do you understand by middleware?

Middleware is a layer of software that is allowed to lie between operating systems and applications. It acts as a pipe to transfer data between the application and operating systems.

In Node.js middleware are functions that sit between the request object ( req ), the response object ( res ). It acts as a filter that has access to both the request and response object.

Below are a few examples of middleware

  • Database middleware
  • Application server middleware
  • Message-oriented middleware
  • Web middleware

Q4. How to connect NodeJS with mongodb?

Q5. How does Promise and Queue work in Node.js?

Promises are specifically designed pattern used to reduce the practice of unintuitive call backs. Promises are generally used with ‘then’ function in the code.

Promises are designed to execute two functions.

  • When the promises are resolved and
  • When the promises are rejected.

A queue is specifically used to control the execution flow. Also, the queue is used to get a solution for a specific problem.

Q6. Describe Node.js event loop and event driver architecture?

Node.js is an application especially called as single-threaded. They are used to provision concurrency by the concept of event and callbacks.

When a task is getting completed, node thread by using the event loop triggers the next function to get executed.

When the event loop triggers, there is an event listener ready to execute the next function. These structural loops are called as event driver architecture.

Q7. How are Promises better than callbacks ?

When there is a completion of any single-threaded we need to tell callbacks what to do next.

Promises are designed in such a way that it comes back with an object (alert) and then we will tell promises about what to do next when there is asynchronous task completion.

Promises are also known as asynchronous callbacks. They are better callbacks because they make error handling across multiple asynchronous calls more effortless than callbacks.

Q8. What is JIT and how is it related to Node?

Q9. What is callback hell?

Callback Hell is also known as the pyramid of doom. It is an anti-pattern seen in the code of programmers who are not wise in the ways of asynchronous programming.

Q10. Why do you use forever with Node.js?

The purpose of Forever is to keep a child's process running continuously and automatically restart it when it exits unexpectedly. It starts a script as a daemon.

Q11. Why Node.js is based on single threaded architecture?

Node.js is based on single-threaded architecture because it has one call stack and one memory heap. As expected, it executes code in order and must finish executing a piece of code before moving onto the next

Q12. What is the difference between Node.js and Ajax?

The difference between Node. js and Ajax can be stated as, Ajax or Asynchronous JavaScript and XML is a client-side technology, often used for updating the contents of the page without refreshing it. Whereas Node. js is Server-Side JavaScript, used for developing server software.

Q13. What is REPL in Node.js?

REPL stands for Read-Eval-Print-Loop.In Node.js REPL is a virtual environment that allows developers to read, write and execute JavaScript code. To launch Node REPL simply open command prompt on windows and type node.


Q14. What is a Buffer in Node.js?

The Buffer class in the Node JS is used to store raw data in a raw memory allocation outside the V8 heap. It is used to handle the octet streams while dealing with the TCP streams. A Buffer class is like an array but stores the stream data in 7667ytghfixed-size, raw memory allocation. The buffer class is within a global scope so users don’t need to use the require('buffer').Buffer.

Q15. What are Global object in Node.js?

As the name suggests, global objects are available in all the modules as they are global in nature. Developers can use it directly in their application instead of including it to use it. Some of these global objects are not actually in the global scope but in the module scope.

Some important global objects are:-  __dirname, __filename, console, process, buffer, setImmediate(), setInterval(), setTimeout(), clearImmediate(), clearInterval, clearTimeout.

These global objects can be modules, functions, strings, and objects.

Q16. What is the use of Zlib in Node.js?

The Zlib module in the Node JS is used to compress and decompress the files. This module is implemented using Gzip and Deflate/Inflate. It provides the way for zipping and unzips files. This module comes with a lot of built-in properties and methods for working with compression and decompression. Before using the module,

you should include it in your file by using the following line.

var Zlib = require('zlib')

Q17. What is NPM? How to uninstall a dependency using npm?

NPM (Node Package Manager) is a JavaScript Package manager. It consists of a command-line, online database, public, and private packages. You can download the required package for your application by using the npm. It is free to use registry and the largest software registry in the world. Released in 2010, npm is written in JavaScript. The npm has over 477,000 packages present in the main npm registry.

To uninstall a dependency using the npm, you can simply use the following statement in the npm command line.

npm uninstall <package-name>

Q18. What is Piping in Node?

The main objective of piping is to read data from a readable stream of data, and it functions to write the same data into a write stream.

In the node applications, the stream of data between the two arguments is piped together. This is done by using the pipe method.

Q19. Which module is used for buffer based operations in NodeJs?

The Buffer module is used by the Node JS for implementing buffer based operations. Buffers are a chunk of memory created outside of v8 heap and are implemented using a JavaScript typed array. It is a globally available module to enable the interaction with octet streams in TCP streams.

Q20. Explain Chaining in NodeJs?

In NodeJS, chaining helps to chain asynchronous fusions.

Chaining process consists of

  • Parallel mode – The chaining runs the asynchronous functions in parallel to the other functions.
  • Serial mode – The chaining does not run the asynchronous function if any other functions are engaged.

Q21. What is difference between return and callback?

Difference between return and callback

When we use call back function, if there is an asynchronous function, it does not return with a value. Instead, we have to identify and make the further process.

When we use a promise function, it returns with an alert (value) to us if there is any asynchronous function. So immediately we could able to react to it.

Final Words :

Express.js is a free and open-source software and web application framework for Node JS which was designed for the development of web applications and API’s. It is also the standard server framework for Node JS. It was developed by TJ Holowaychuk on 16th November 2010. Along with the MongoDB database and Angular JS frontend framework, express JS is the backend part of the MEAN stack. With the help of this, you will be able to manage everything from routes to handling requests and views. It even provides a robust set of features for various web and mobile applications.

About Author :

  • Author of Node JS Interview Questions

    Ketan Chauhan

    Ketan is a Software developer from Bengaluru, Karnataka, India.He works on latest Javascript technologoies like Angular, Node JS, React JS. He has also good knowledge of PHP and its frameworks like CodeIgniter, CakePHP,Laravel, Zend.He is always ready for learning new technologies. He loves playing Table tennis, watching and answersing developers queries.

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