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Table of contents
Most Asked MEAN Stack Developer Interview Questions & Answers   
1. Define Mean Stack.
2. What is the definition of Scope in JavaScript?
3. Define Node JS?
4. What is REPL in Node.Js?
5. Is Node.js entirely dependent on a single thread?
6. What is the function of MongoDB?
7. What is the aim of ExpressJS?
8. What is the aim of AngularJS?
9. Explain the operation of the Centralized Workflow.
10. Explain the concept of containerization.
11. Explain the Node.Js operating mechanism?
12. Define the callback feature from the aspect of Node.Js.
13. Describe Express.js routing?
14. What exactly is Dependency Injection?
15. Compare SQL databases and MongoDB.
16. Define BSON in MongoDB.
17. What is DATA modeling?
18. Differentiate between Node.js, AJAX, and jQuery.
19. What are the functions of Indexes in MongoDB?
20. What is a CSS Grid System?
21. What is CORS, and how do you enable it?
22. Define Cross-Site Scripting (XSS)?
23. In Javascript, describe WeakSet.
24. Explain the Node.js Event Emitter.
25. What is the difference between ES5 and ES6?
26. In Javascript, explain WeakMap.
27. What is the Node.js approach to Child Threads?
28.  What is Routing Guard in Angular?
29. Differentiate between “ == “ and “ === “ operators.
30.  What is NaN in JavaScript?
Last Updated: Jun 12, 2024

Mean Stack Interview Questions and Answers(2023)

Author Ashish Sharma
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Anubhav Sinha
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12 Jun, 2024 @ 01:30 PM

Mean Stack is a set of JavaScript development tools for designing and building web apps. MEAN is a full-stack development toolkit designed to create web apps that are quick and reliable. 

Mean Stack Interview Questions

If you are preparing for a mean stack interview in the future and are looking for a quick guide before your interview, then you have come to the right place. In this article, we will discuss the top 30 mean stack Interview questions, which consist of all types of mean stack Interview questions.

Read more, Html interview questions And Operating System Interview Questions

Most Asked MEAN Stack Developer Interview Questions & Answers   

1. Define Mean Stack.

Ans: The MEAN stack is a set of JavaScript-based technologies to create online applications. The full form of MEAN is MongoDB, ExpressJS, AngularJS, and Node.js.    

2. What is the definition of Scope in JavaScript?

Ans: Each function in JavaScript has its scope. The scope is a set of variables and rules for accessing those variables by name. Only code within the function has access to the function's scoped variables.

A variable name must be unique when it is in the same scope. A scope can be nested within another scope. When one scope is nested within another, the code can access the variables from any scope.

3. Define Node JS?

Ans: Node.js is a server-side programming language used to build flexible projects. It has several advantages over other server-side languages, the most notable is non-blocking I/O. It is a JavaScript-based platform or runtime based on the V8 JavaScript engine in Chrome. It's a single-threaded software that uses concurrency models based on the event loop. Instead of blocking the execution, it registers a callback, allowing the programs to continue running. As a result, Node.js can manage all of these concurrent tasks without executing multiple threads, which can scale quite well.

4. What is REPL in Node.Js?

Ans: REPL stands for Reading Eval Print Loop. It also evaluates datasets and displays the results. It is essential to understand that REPL replicates the environment of a Linux shell. REPL is related to the successful completion of the tasks listed below.

  • Print: Print links with printing the results derived from the command.
  • Read The read command links with reading the inputs provided by the user. It stores the structure inside the function.
  • Loop: Loop would continue to twist the command until the user uses Ctrl+C.

5. Is Node.js entirely dependent on a single thread?

Ans: Yes, Node.js can run entirely on a single thread. However, you should be aware that it is only a theory underlying the architecture of Node.Js. Apart from being involved in operating a single thread mechanism, it also uses callbacks and events to meet a wide range of requirements. It is also important to notice that Node.Js has an optimized design. Because of its simplified architecture, it can employ both C++ and JavaScript, resulting in maximum efficiency. The JavaScript executes on the server's side. The C++ library ensures the processing of non-sequential I/O through background workers.

6. What is the function of MongoDB?

Ans: MongoDB is a document-oriented database manager designed for massive data storage. It saves data in binary JSON format and implements the documentation and collection concepts. MongoDB is a cross-platform NoSQL database with high scalability, performance, and flexibility that enables seamless indexing and querying.

7. What is the aim of ExpressJS?

Ans: ExpressJS is a web application framework for hosting and supporting Node.js projects. It is an open-source framework distributed under the MIT license. ExpressJS handles the workflow between the database and the front end and ensures data transfers securely and smoothly. It has robust error handling and web design capabilities to help with web development.

8. What is the aim of AngularJS?

Ans: AngularJS is the JavaScript framework. we can add it to the HTML page with a <script> tag.

AngularJS extends the HTML attributes with Directives and binds the data with HTML Expressions.

Google maintains AngularJS, a front-end, open-source web application development framework for constructing single-page applications. It enables Web Developers to use HTML as their template language and the HTML syntax to represent a web app's components properly.

Must Read Web Developer Interview Questions

9. Explain the operation of the Centralized Workflow.

Ans: The centralized workflow employs a central repository as the single entry point for all project modifications. All changes are in the main branch, which is the default development branch. To begin, developers replicate the primary repository. They edit files and make changes to their local project copies. These new changes save locally. Developers push their local main branch to the central repository to make changes to the official project. Before publishing their feature, developers must get the modified central commits and rebase their changes on top of them. Compared to other processes, the Centralized Workflow has no well-defined branching patterns or pull requests.

10. Explain the concept of containerization.

Ans: Containerisation is a virtualization method that emerged as an alternative to standard hypervisor-based virtualization. In containerization, the operating system is shared by all containers rather than duplicated for each virtual machine. For example, docker provides a container virtualization platform that is an excellent alternative to hypervisor-based setups.

11. Explain the Node.Js operating mechanism?

Ans: It is important to note that when a Node.Js application is activated, it facilitates the creation of a single thread. When Node.Js receives a request, it completes the processing before proceeding to the next request. It is also important to remember that Node.Js operates via the event loop. It also makes use of callback mechanisms and manages numerous user requests. An event loop refers to a function that initiates all event handlers. It is also important to remember that Node.Js processes a request and normally attaches a callback function. When the response is ready, the event calls the callback function, which sends the response to the user's query.

You can also visit: Python Interview Questions

12. Define the callback feature from the aspect of Node.Js.

Ans: Node.Js makes significant use of callbacks, which allow it to activate them when a task completes. In this regard, it is important to highlight that most Node.Js API constructs in a way that callbacks are supported. When the file read operation finishes, it will invoke the callback function and pass the file's contents. As a result, there is no wait or blocking due to the presence of File I/O. That's why Node.js can be very scalable, as it involves processing more requests without waiting for the results.

13. Describe Express.js routing?

Ans: Frameworks utilize routing to determine how a URL/endpoint responds to/is handled by the server. Express is a good tool for managing application routing. The following is some basic Express routing code.

var express = require(‘express’)

var app = express()

// respond with "mean stack interview questions" when a GET request is made to the homepage

app.get(‘/’, function (req, res) {
  res.send('Mean stack interview questions')


14. What exactly is Dependency Injection?

Ans: Dependency injection is simple to design loosely connected components, which often implies that components consume interface-defined functionality without knowing which implementation classes are utilized.

15. Compare SQL databases and MongoDB.

Ans: SQL databases organize data into tables, rows, columns, and records. Data is stored in a pre-defined data model, which is not very flexible for today's rapidly increasing real-world applications. MongoDB employs a flexible, easily adjusted, and extended structure.

16. Define BSON in MongoDB.

Ans: BSON is a binary serialization format that MongoDB uses to store documents and make remote procedure calls. BSON expands the JSON format to provide more data types, ordered fields, and fast encoding and decoding across languages.

17. What is DATA modeling?

Ans: Data modeling assists in visually representing data while simultaneously imposing corporate standards, regulatory compliances, and government policies on the data. It ensures consistency in naming standards, default values, semantics, data security, and data quality.

18. Differentiate between Node.js, AJAX, and jQuery.

Ans: Node.js, AJAX, and jQuery are all advanced JavaScript implementations. 

Node.js is a server-side platform for creating client-server applications. In contrast, AJAX, Asynchronous Javascript, and XML) are client-side scripting techniques used to render a page's contents without refreshing it. AJAX is used primarily to display dynamic pages. jQuery is a JavaScript package that works with AJAX, DOM traversal, and looping. It includes a variety of useful utilities to work with JavaScript programming.

19. What are the functions of Indexes in MongoDB?

Ans: Indexes are used in MongoDB to support and facilitate the efficient execution of queries. MongoDB needs to run a collection scan without indexes, which means it must scan every item in a collection and select the appropriate documents that match the query statement. MongoDB can use the index to minimize the number of records to inspect if each query has an appropriate index.

20. What is a CSS Grid System?

Ans: A grid system in CSS is a structure used for storing content vertically and horizontally in a uniform and understandable manner. Rows and columns are the two main components of grid systems. Simple, Pure, Flexbox, Bootstrap, and Foundation are some of the most popular grid systems.

21. What is CORS, and how do you enable it?

Ans: CORS (cross-origin resource sharing) is a protocol that manages cross-origin requests. CORS enables servers to determine who (i.e., which sources) can access the server's assets, among other things.

The Access-Control-Allow-Origin HTTP header specifies which foreign origins are permitted to access the content of your domain's pages via scripts using methods such as XMLHttpRequest.

22. Define Cross-Site Scripting (XSS)?

Ans: By using the Cross-Site Scripting (XSS) approach, users mistakenly launch malicious scripts (also known as payloads) by clicking on untrusted links, and these programs pass cookies information to hackers.

23. In Javascript, describe WeakSet.

Ans: A Set in javascript is a collection of unique and ordered elements. WeakSet is the collection of unique and ordered elements with the following differences:

Weakset holds objects, no other types.

A weakly referred item is contained within the weakset,  Which means that if the item within the weakset lacks , it will be junk collected.

WeakSet offers only three methods: add(), remove(), and has().

const data = new Set([1,2,3,4]);
console.log(data);// Outputs Set {1,2,3,4}

const data2 = new WeakSet([3, 4, 5]); //Throws an error

	let obj1 = {message:"Hello Ninjas"};

const data3= new WeakSet([obj1]);
console.log(data3.has(obj1)); // true


24. Explain the Node.js Event Emitter.

Ans: An event module provides in Node. Js allows you to create and manage unique events. It is important to note that the event module includes the game emitter class, which can be used to collect and raise personalized events. It would be best if you also remembered that when an event emitter detects an error, it emits an error case. If a new user is added, it sends a sample with the new user's name. When the current user is disabled, it sends a demonstration using the distinct user's name.

25. What is the difference between ES5 and ES6?

Ans: ES5 (ECMAScript 5): It is ECMAScript's 5th edition, which was standardized in 2009. This standard has been implemented in almost all recent browsers.

ECMAScript 6 (ES6) and ES2015 (ES2015): The ECMAScript 6th edition was standardized in 2015. Most recent browsers support this standard to a certain level.

To know more about jQuery interview questions click here.

26. In Javascript, explain WeakMap.

Ans: The map is used in javascript to store key-value pairs. The key-value pairs might be either primitive or non-primitive. WeakMap is similar to Map, but with the following important differences:

  • In weakmap, the keys and values should always be objects.
  • If no references exist,  it will be garbage collected.
const data1= new Map();
data1.set('Value', 10);

const data2 = new WeakMap();
data2.set('Value', 22.3); // Throws an error

let obj = {name:"Ninjas"};
const data3 = new WeakMap();
data3.set(obj, {age:13});


27. What is the Node.js approach to Child Threads?

Ans: Node.js is a single-thread process. It does not display the developer thread management methods or child threads. Js shows child threads for specific operations, such as asynchronous I/O, but these are executed on the backend and do not run any JavaScript code. If threading functionality is necessary for a Node.js application, tools such as the ChildProcess module will get available to enable it.

28.  What is Routing Guard in Angular?

Ans: Angular’s route guards are interfaces that can tell the router whether it should allow navigation to a requested route or not. Routing Guard makes this decision by looking for a true or false return value from a class that implements the given guard interface.

There are five different types of guards called in a particular sequence. The router’s behavior is modified differently depending on which guard is used. The guards are:

  • CanActivate
  • CanActivateChild
  • CanDeactivate
  • CanLoad
  • Resolve


Consider the below example:

import { Injectable } from '@angular/core';
import { Router, CanActivate } from '@angular/router';
import { AuthService } from './auth.service';

export class coding ninjas implements CanActivateclass {
  constructor(public auth: AuthService, public router: Router) {}
  canActivateclass(): boolean {
    if (!this.auth.isAuthenticated()) {
      return false;
    return true;


29. Differentiate between “ == “ and “ === “ operators.

Ans: They are both comparison operators. The difference between the two is that "==" compares values whereas " === " compares both values and types.

var x = 3;
var y = "3";

(x == y)  // Returns true as the value in x and y are the same
(x === y) // Returns false as the type of x is "number" and the type of y is "string".


30.  What is NaN in JavaScript?

Ans: NaN represents the “Not-a-Number” value. It indicates a value which is not a legal number.
type of NaN returns a Number.
To verify if the number is NaN, we will use the isNaN() function,

Note- isNaN() function changes the given value to a Number type, and then equates it to NaN.

isNaN("Hello ninjas")  // Returns true
isNaN(1234)   // Returns false
isNaN('1')  // Returns false, as '1' will convert to a Number type which results in 0 ( a number) 
isNaN(true) // Returns false, as true will convert to Number type results in 1 ( a number)
isNaN(true) // Returns true
isNaN(undefined) // Returns true


In this article, we have discussed mean stack interview questions in detail. We started with a basic introduction to mean stack, then we discussed some introductory mean stack interview questions, intermediate mean stack interview questions, and advanced mean stack interview questions.

After reading about the mean stack interview questions, are you not feeling excited to read/explore more articles on interview questions? Don't worry; Coding Ninjas has you covered. Other linked list related problems Managerial Round Interview QuestionsFlutter Interview QuestionsWeb API Interview QuestionsMachine Learning Interview QuestionsSQL Interview Questions, and Selenium Interview Questions.

You can also consider our Mern Stack Course to give your career an edge over others.

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