Top 41 Node.Js Interview Questions & Answers You Need To Know in 2020

Attending a Node.js interview and wondering what are all the questions and discussions you will go through? Before attending a Node.js interview, it’s better to have an idea about the types of Node.js interview questions will be asked so that you can mentally prepare answers for them.

Node.js is a simple yet very popular server-side scripting tool that uses JavaScript. You can create something as simple as a command-line program to even complicated enterprise-level web applications using Node.js. A lot of companies you shall notice demands for a Certified Node.js Developer, so to handle the entire server-side. You can find the need of Node.js at various levels in your career point. 

Node.js Interview Questions & Answers 2020

Let’s segregate the article into three sections:

  1. Basic Level Node.js Interview Questions & Answers
  2. Intermediate Level Node.js Interview Questions & Answers
  3. Expert Level Node.js Interview Questions & Answers

1. Basic Level Node.js Interview Questions & Answers

Q.1) What is the difference between Node.js and JavaScript?

Node.js is an interpreter and environment for JavaScript, which is mainly used for accessing or executing any non-blocking operation for any operating system. The running engine here is Google Chrome. 

Whereas, JavaScript is a programming language which is used for any client-side activity for a web application. The running engine here is Firefox, Safari, Google Chrome, etc.

Q.2) What is Node.js?

Node.js is a lightweight yet powerful framework that is developed on Chrome’s JavaScript engine. It compiles JavaScript straight into the native machine code. It is used in building server-side web applications and extends JavaScript API to give usual server-side functionalities. People use this framework for large-scale application construction like single-page applications, video streaming sites, and other web-based applications. 

Q.3) List some advantages of using Node.js

  • It is fast because it is created on the Chrome JavaScript engine, which makes its library faster in executing code.
  • It is Asynchronous because it never waits for an API to give back data.
  • It is scalable because of its event mechanism, which enables the server to respond in a non-blocking way.
  • It is an open-source, offering an incredible open-source community, which has created some fantastic modules which added more power to Node.js apps.
  • Node.js never buffers data because the output is in chunks.

Q.4) List the differences between Angular and Node.js?

Angular is an open-source used for web application & Node.js is basically a cross-platform run-time environment for apps.

Angular is written in TypeScript & Node.js is written in languages like C, C++, and JavaScript.

Angular is mainly used for creating single-page client-side web apps & Node.js is mainly used for creating scalable and fast server-side networking apps.

Angular is a web application framework & Node.js has several different frameworks like Partial.js, Sails.js, and Express.js, etc.

Angular is best used for creating highly active and interactive web apps & Node.js is best used for developing smaller projects

Angular helps in splitting an app into MVC components & Node.js helps in creating database queries 

Angular is well used for creating real-time applications & Node.js well used for situations where faster and more scalable is needed

Q.5) Why is Node.js single-threaded?

It works on the single-threaded model instead of typical thread-based implementation in order to aid async processing. Using async processing, an application can execute better and is more scalable under web loads.

 Q.6) How do Node.js works?

Node.js is a virtual machine that runs on a v8 environment using JavaScript as its scripting language. It works on a single-threaded model and a non-blocking I/O, which gives a high rate as it can handle a larger number of simultaneous requests.  Because it uses an HTTP module, it can run on any standalone web server.

Q.7) Where can we use Node.js?

Node.js can be used to create: 

  • Network Applications
  • Real-Time Web Applications
  • General Purpose Applications
  • Distributed Systems

Q.8) Node.js has how many types of API functions?

You can find two types of API functions in Node.js, namely Synchronous, blocking functions, and Asynchronous, non-blocking functions. 

Q.9) What is the distinction between the Asynchronous and non-blocking function?

Asynchronous (not synchronous) functions are those using which we can make Asynchronous HTTP requests that do not wait for a server to respond. These functions continue to return to the request for which it has already received the server response.

Non-blocking functions are used in relation to I/O operations. They quickly respond with whatever data is available and keeps running as per the requests. In the event where there is no answer returned, the API returns swiftly with an error. 

Q.10) Explain Event-driven programming

It is a programming approach that mainly uses events for triggering several functions. Events could be a keypress, mouse click, etc. When an event is triggered, the call back function is performed that is preregistered with the element. This method mainly uses the publish-subscribe pattern. It is due to this method Node.js is faster than other technologies. 

Q.11) In the context of Node.js, explain REPL

REPL in Node.js means Read, Eval, Print, and Loop. It depicts a computer setting such as a Unix/Linux shell or window console or where any command can be registered, and then the system can reply with an output. Node.js comes packed with a REPL environment by default. REPL can execute the following tasks:

  • Read: It reads the user’s input, converts it into JavaScript data-structure, and then stores it in the memory.
  • Eval: it receives and assesses the data structure.
  • Print: It prints the ultimate result.
  • Loop: It loops the given command until CTRL+C is pressed twice.

Q.12) List down the jobs which should be done asynchronously using the event loop?

  • I/O operations
  • Heavy computation
  • Anything requiring blocking

Q13) Why does Google use the V8 engine for Node.js?

V8 runtime engine converts JavaScript code into native machine code, resulting in fast-running applications. This Chrome engine significantly speeds up the execution and response processes.

Q14) What are the benefits of using Node.js?

As we discussed earlier, Node.js is built on the V8 engine, which makes its library execute code swiftly. A server-based on Node.js does not wait for an API to return data, meaning that it is asynchronous. Moreover, Node.js is highly scalable as its event mechanism responds in a non-blocking manner.

There is also no buffering in Node.js applications. Over the years, a sizable open source community has emerged, contributing excellent modules and providing additional capabilities to Node.js applications.

2. Intermediate Level Node.js Interview Questions & Answers

Q.15) What is a test pyramid?

The diagram that explains the ratio of how many unit tests, integration tests, and the end-to-end test is needed to be written for the successful building of the project is called a test pyramid.

Q16) What is the role of the Express.js package?

Express.js is a framework that assists the management of data flow between server and routes in server-side applications. This flexible framework is built on top of Node.js, specifically on the middleware module called connect. In turn, the connect module uses the HTTP module to communicate with Node.js. Therefore, integrating with Express.js becomes easy if you are working with any of the middleware modules based on connect. 

Q17 ) What is the role of the assert module in Node.js?

Assert allows you to write tests. In Node.js, it is an internal module that provides a set of assertion tests for examining invariants. You can use the require(‘assert’) code for other applications.

Q.18) What is an error-first callback in Node.js?

Error-first callback in Node.js are used to pass errors and data. The first parameter that passes these functions has to be an error object. The other parameters represent are the attached data. If there are no errors, or issues, you can move ahead with the subsequent arguments.

var myPost = new Post({title: ‘Myexample’});,myInstance){



//handle error and return


//go ahead with `myInstance`


Q19) What is the purpose of the package.json file?

The package.json file in Node.js contains the metadata of the project. It is the heart of the application, where you define the properties of a package. The file’s metadata can be further categorized into the following:

  • Properties like project name, license, author, current module version, project description, etc.
  • You can also include necessary information about your project by writing it directly into the package.json file.

Q.20) What is the use of module.exports?

To blend all the alike codes into a single unit of code, which can be executed by moving all related functions into a particular file, we need to use module.exports in Node.js. For example, you have a file named greet.js that comprises the two functions as shown below:

module.exports = {

greetInHindi: function(){

return “NAMASTE”;


greetInEnglish: function(){

return “Hello”;


The module.exports offers two functions which can be imported in a separate file using below code:

var myGreets = require (“./greet.js”);

myGreets.greetInHindi() //NAMASTE

myGreets.greetInEnglish() //Hello

Q.21) What is a Reactor Pattern in Node.js?

Reactor Pattern in Node.js is a theory of non-blocking I/O operations. This pattern gives a handler that is connected with each I/O operation, and as soon as an I/O request is created, it is then submitted to a demultiplexer. This demultiplexer is a notification interface that is able to handle concurrency in non-blocking I/O mode.

It also assists in handling each and every request in the form of an event and then place each event in a line. It is thus resulting in the generation of the Event Queue. Concurrently, we have our event loop, which repeats the events present in the Event Queue.

Q.22) What are LTS releases of Node.js?

LTS means Long Term Support version of Node.js that gets all the important bug fixes with security updates and performance enhancements. All these versions are valid for a minimum of 18 months and primarily focuses on security and stability issues. The changes done to the LTS versions are limited only to fixing bugs, npm, security upgrades, documentation and performance speedups. 

Q.23) What do you understand by callback hell?

Callback Hell is also called the Pyramid of Doom. It is a pattern that happens due to extreme nested callbacks that are not readable. It usually comprises multiple nested callback functions making the code hard to read or debug. It is mainly due to improper implementation of the asynchronous logic.










Q24) List the input arguments of async.queue.

In Node.js, async.queue takes two arguments as inputs. These include task function and concurrency value.

Q.25) What is libuv?

It is a Node.js multi-platform support library, which is mainly used for asynchronous I/O. It was initially developed for Node.js, but now it is also used with our system like pyuv, Luvit, Julia, etc. Libuv is basically an abstraction around libev/ IOCP based on the platform, offering users a libev based API. A few of the crucial features of libuv are:

  • File system events
  • Full-featured event loop backed
  • Asynchronous TCP & UDP sockets
  • Asynchronous file and file system operations
  • Child processes

Q.26) Streams in Node.js

Streams enable you to read and process large datasets in Node.js. These objects are data collections resembling strings and arrays. They allow you to continuously read data from a source or write to a destination. In Node.js, there exist four fundamental types of streams – Readable, Writable, Duplex, and Transform. 

Q.27) How do you read and execute files in Node.js?

In Node.js, there are two ways to read and execute files – readFile and createReadStream. The main difference between the two is that readFile is fully buffered and createReadStream is partially buffered. readFile() returns a response only when the entire file is pushed into the buffer, slowing down the processing time.

In contrast, createReadStream treats the process as an event series, splitting the file into chunks and sending back responses one by one. So, it provides an effective way of processing large data files. 

Q.28) Which security implementations are available within Node.js?

Authentication and error handling are the two major security implementations in Node.js.

Q.29) How are child threads handled in Node.js?

You would think that since Node.js is single-threaded, you cannot make use of child threads. Although the process doesn’t generally expose child threads, you can still execute certain asynchronous I/O tasks in the background by using spawn(). With this, the application’s main event loop is not hindered. You can also include the ChildProcess module to use this threading concept explicitly.

3. Expert Level Node.js Interview Questions & Answers

Q.30) What is the use of NODE_ENV?

If your project is at the production level, Node.js promotes the convention of making use of the NODE_ENV variable to flag it. This helps in making a better decision while the project is created. Further, when you set your NODE_ENV to production, your application does work faster around three times.

Q.31) In Node.js, what is the difference between createReadStream and readFile

Node.js offers two ways to read and operate files that are using readFile and CreateStream. readFile() is a completely buffered process that responds only when the entire file is pushed in the buffer and read. It is a memory-intensive process, which gets very slow for larger files.

Whereas in the case of createReadStream is partially buffered, which takes the complete process as an event series. The file is divided into big chunks, which are then processed and sent back as a response one at a time. Once completed, they are then removed from the buffer, making it more efficient for processing larger files. 

Q.32)Explain the usage of buffer class in Node.js

Buffer class in Node.js stores the raw data like an array of integers. It corresponds to a memory allocation outside the V8 realm, meaning that it is a global class. The class can be accessed without importing a buffer module in Node.js. The need for buffer class arises because JavaScript is not compatible with binary data.

Q.33) Differentiate between spawn() and fork()

You use the spawn() in Node.js to launch a new process. With the provided set of commands, this process activates just one copy of the node module on the processor. Since no new V8 instance is created, spawn() becomes particularly helpful when your child process returns a vast amount of data.

Conversely, the fork() method executes a new instance of the V8 engine. This means that multiple workers are running on a single Node-based code for various tasks.

Q.34) Front-end and back-end development

Front-end development is based on asynchronous requests and AJAX, while back-end development stands on a server architecture. The former uses markup and web languages like HTML, JavaScript, CSS, etc. for SEO purposes. Whereas the latter harnesses programming languages Python, Ruby, and others for backup. Front-end development is more accessible as compared to back-end development.

Q.35) List the steps of using the control flow function.

The code executed between the async function calls in Node.js is the control flow function. The working of the function can be explained with the following steps:

  • First, control the order of execution 
  • Then, collect the required data 
  • Next, limit the concurrency
  • Finally, invoke the next step of the program

Q.36) Name the timing features of Node.js.

Node.js provides a Timers module, which comprises various functions for running the code after a given period of time. The various functions provided by this module:

setTimeout/clearTimeout – It is used to program code execution after some milliseconds

setInterval/clearInterval – It is used to perform a block of code several numbers of times

setImmediate/clearImmediate – It is used to run code at the end of the current event loop cycle

process.nextTick – It is used to program a callback function that needs to be triggered in the next iteration of the Event Loop

Q.37) Tell us about the theory of Punycode in Node.js?

Punycode is an encoding syntax. It is used to translate the Unicode (UTF-8) string of characters into a basic ASCII string of characters. This is needed as hostnames only recognize ASCII characters. It comes in default for all the versions after 0.6.2. However, if you wish to use it for older versions, you can do it by using the syntax: 

  punycode = require(‘punycode’);

Q.38) Differentiate between Node.js and Ajax?

Node.js is a server-side JavaScript, contrary to Ajax, which is a client-side technology. Ajax is mainly to update or edit the webpage without even the need to refresh the page. Whereas, Node.js is needed to develop the server software that is typically performed by the servers rather than the web browsers.

Q.39) Does Node.js offer any Debugger?

Node.js do offer a simple TCP based protocol as well as an inbuilt debugging client. If you wish to debug your JavaScript file, you can use the argument node debug [script.js | -e “script” | <host>: <port> ], followed by the js file name that you want to debug.

Q.40) What are global objects?

You can use global objects in Node.js without needing to include them explicitly. These can be modules functions, strings, etc. available in the module scope of the application. Sometimes, you may find them in the global scope.

Q.41) Explain the exit codes of Node.js.

The exit codes are a set of distinct codes that are used to finish a particular process. It could include the global object too. Below are some examples of exit codes used in Node.js:

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


Coming to the end of our collection of some of the most asked Node.js interview questions and answers, we hope you find them valuable and are able to impress your interviewers by answering them right. 

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