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.

Q31. What is the fork in node JS?

Fork() is used to spawn a new Node.js process. It invokes a specific module with an IPC communication channel, thus enabling the sending of messages between a parent and child.


const { fork } = require('child_process');

const forked = fork('child.js');

forked.on('message', (msg) => {
     console.log('Message from child', msg);

forked.send({ hello: 'world' });

Q32. What is the difference between the node js child process and clusters?
Child Process Clusters
It is a module of Node.js containing sets of properties and functions helping developers throughout the forking process. These can be easily spun using Node's child_process module and can communicate with each other using a messaging system.
It occurs when you have two or more node instances running with one master process routing. It spawns a new script or executable on the system.
Q33. What is callback hell, and how can it be avoided?

Callback hell is a situation in Javascript when you face callbacks within callbacks or nested callbacks.

It looks somewhat like this:

firstFunction(args, function() {
   secondFunction(args, function() {
      thirdFunction(args, function() {

There are two significant ways to avoid Callback Hell in NodeJS:

1. Using Promises

const makeBurger = () => {
    return getChicken()
    .then(chicken => cookChicken(chicken))
makeBurger().then(burger => serve(burger));

See, it is just more easy to read and manage in comparison to the nested callbacks.

2. Use Async/Await

Using Asynchronous functions, we can convert makeBurger into one synchronous code. Also, maybe you can get helpers to getBun and getChicken at the same time, meaning, you can use await with Promise.all. Here's the code:

const makeBurger = async () => {
    const cookedChicken = await cookChicken(chicken);
    return cookedChicken;

Q34. What is the difference between readFile vs. createReadStream in Node.js?
Pure Pipes Impure Pipes
This will thoroughly read the file into the memory before making it available to the user. It will read chunks of a file as per specifications provided by the user.
Since the whole data is sent after it has been loaded, it will take time for the client to reach and hence, is slower. Since it reads files in chunks, the client will read the data faster than in readFile.
It is easier to clean the non-used memory by Node.js in this. It is much more difficult for Node.js to clean up memory in this case.
It will not scale the requests at a given time, preferably all at once. It will pipe the content directly to the client using HTTP response objects, making it time-saving.

Note: Our aim while creating nodejs interview questions, is to help you grow as a Node Developer. The questions mentioned here have been asked by leading organizations during technical rounds of the interview process.

Q35. How to pass an array in insert query using node js?

The array of records can easily be bulk inserted into the node.js. Before insertion, you have to convert it into an array of arrays.


var mysql = require('node-mysql');
var conn = mysql.createConnection({
     // your database connection

var sql = "INSERT INTO Test (name, email) VALUES ?";
var values = [
    ['best interview question', '[email protected]'],
    ['Admin', '[email protected]'],

conn.query(sql, [values], function(err) {
     if (err) throw err;

Q36. How to use Async Await with promises in node js?
  • Step1. Install Async first with "npm install async" command
  • Step2. Call the async in your file with you will use async.
    var async = require("async");
  • Step3. Make an async function and call await function inside async function.
    let phoneChecker = async function (req, res) {
         const result = await phoneExistOrNot();
    exports.phoneChecker = phoneChecker;

    await will work only under async function.

    For example: here is " phoneChecker " is async function, and phoneExistOrNot is await service.
  • Step4. Now you can write your logic in await function.
    let phoneExistOrNot = async function (req, res){
        return new Promise(function(resolve, reject) {
            db.query('select name, phone from users where phone = 123456789 ', function (error, result) {
                 if(error) {
                 } else {
Q37. Explain the difference between const and let in node js?
Answer let const
1. It can be reassigned, but can’t be redeclared in the same scope. It can be assigned an initial value, but can’t be redeclared in the same scope, and can’t be reassigned.
2. It is beneficial to have for the vast majority of the code. It can significantly enhance your code readability and decrease the chance of a programming error. It is a good practice for both maintainability, readability and avoids using magic literals
Q38. What is UUID, and how you can generate it in Node.js?

A UUID is a Universal Unique Identifier is a method for generating ids that have been standardized by the Open Software Foundation (OSF).

You can generate UUIDs in Node.js through the node-UUID. It is a speedy and straightforward way of generating Version 1 & 4 UUIDs.

Here's how to generate UUIDs
  • Install the node-uuid through the npm manager using npm install uuid.
  • Use it in your script like this:

const uuidv1 = require('uuid/v1')
const uuidv4 = require('uuid/v4')
var uuid1 = uuidv1()
var uuid5 = uuidv4()

Here is how your output would look. Although, due to the nature of UUIDs, your generated IDs may be completely different.


uuid1 v1 => 6bf958f0-95ed-17e8-sds37-23f5ae311cf6
uuid5 v4 => 356fasda-dad8d-42b7-98b8-a89ab58a645e


Q39. How to connect MySQL database using node js?

If you don't install MySQL then you can install MySQL by npm install mysql.

Create Connection

You can write connection code in a single file and call in all pages where you need to interact with database.

var mysql = require('mysql');
var con = mysql.createConnection({
host: "localhost",
user: "your database username",
password: "database password"

con.connect(function(err) {
if (err) throw err;
console.log("Database Connected!");


Q40. What is Tracing in Node.js?

Tracing is a mechanism in Node.js to provide a centralized tracing information method, which is generated by V8, Node.js core, and the userspace code. It can be enabled with the --trace-event-categories command-line flag or by using the trace_events module.

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...