MEAN Stack Interview Questions and Answers

Mean Stack Interview Questions And Answers from Codingcompiler. Are you planning a great career in Mean Stack and have an interview ahead? Then you could have look at this full list of Mean Stack interview questions & Answers which helps you to clear your interview process.

The Average salary for Mean Stack Developer ranges from $56,043 to $112,897 (approximately).

However, to lead a  career as a successful Mean Stack Developer you should also prepare for AngularJS Interview Questions, which is the next important skill set required. Here is the list of frequently asked Mean Stack Interview Questions that helps you to crack your job interview.

MEAN Stack Interview Questions

1. What is Mean Stack?
2. What is Node.js?
3. What are the key features of Node.js?
4. What are the IDEs which can be used for Node.JS development? 
5. What is Express?
6. What does Express.js do in the MEAN stack?
7. What Is The Difference Between Angular.js And Node.js?
8. What Is Mongoose?
9. What is Routing Guard in Angular?
10. How to install express?

MEAN Stack Interview Questions & Answers

1. What is Mean Stack?
Mean Stack is the Collection of 4 JavaScript-based technologies like AngularJS, Express, Node, and MongoDB. Mean Stack is a full-stack JavaScript that is used to develop web applications.

2. What is Node.js?
Node.js is a JavaScript-based runtime platform that executes the JavaScript code on any platform outside of a browser. Node.js is based on Google Chrome’s JavaScript v8 engine.

It is also called a single-threaded program that utilizes the simultaneous models that depend on the event loop circle. Rather than obstructing the execution, it enrolls a callback which enables the applications to run. In this way, according to it, Node.js can deal with all these simultaneous tasks without making the multiple thread execution which can be scaled entirely well.

3. What are the key fetures of Node.js?

  • Open Source: Node.js is an open-source stage. It implies that the copyright holder has given different privileges of editing, studying and distributing the software/product to anybody for any reason.
  • Simple and Fast: As Node.js is based on Google Chrome’s V8 JavaScript motor, its libraries are very advanced and hence they are ready to run the code at a quicker speed.   
  • High Scalability: Node.js is highly scalable and utilized by an event mechanism. Node.js is profoundly versatile and helps the server in a non-blocking reaction.
  • No Buffering: Node.js is having a very good special feature and i.e; it does not buffer any data. They simply yield the data in lumps.
  • No Buffering: Node.js is having a very good special feature and i.e; it does not buffer any data. They simply yield the data in lumps.
  • Single-Threaded: Node.js is using event looping and able to follow the single-threaded model. It also helps a single user to handle more than one requests. Node.js utilizes one thread model for the event procedure. The reactions of these events may or may not reach the server at once. Moreover, this will not block various tasks which help to make Node.js extremely scalable.
  • Asynchronous:Node.js is having asynchronous libraries. It is very useful and Node.js servers need not wait for the API to send a response and proceed onward to the following API.

4. What are the IDEs which can be used for Node.JS development?      

The IDE’s that most commonly used for Node.JS development are follows:

  1. Cloud9
  2. Atom
  3. Komodo IDE
  4. JetBrains IntelliJ IDEA
  5. Eclipse
  6. JetBrainsWebStorm

5. What is Express?

Express is that the backend part of one thing called the MEAN stack. Express is one of the most important web server used for conveying the web applications to program. ExpressJS allows you to contend with I/O, Server and Routes stuff effortlessly.

The MEAN may be a free and ASCII text file JavaScript software system stack for building dynamic websites and internet applications that has the subsequent components like:
1) MongoDB – the quality NoSQL information.
2) Express.js – The default net applications framework.

Basic MEAN Stack Interview Questions & Answers

6. What does Express.js do in the MEAN stack? 

Express.js enables you to create web applications easily by giving a less difficult interface for making your request endpoints, taking care of treats, and so on than vanilla Node. You could drop it out of the condition, yet then you’d need to do much more work in preparing your web-application. Node itself can do everything but express is implemrted with the Node. However express just envelops it with a more pleasant bundle.

7. What Is The Difference Between Angular.js And Node.js?

Written entirely in
Java Script

Written in C, C++, Java
Single Page client
side web application
Fast and scalable server
side application
Suited for highly
interactive web
Best suited for small size
UsageUsed for real time
applications like
instant messaging
Highly useful when
scalable and faster application
is required
InstallationRequire Angular JS
file like any
JavaScript file
Need to install Node.js
on system
Frame Works
It is a web
framework in
Has many different

8. What Is Mongoose?

Mongoose is an Object Document Mapper (ODM). This means that Mongoose allows you to define objects with a strongly-typed schema that is mapped to a MongoDB document.

9. What is Routing Guard in Angular?

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

10. How to install express?

To install Express temporarily and not add it to the dependencies list.Run below command to install express

npm install express –save

11. Explain Mongoose?

Mongoose is a MongoDB Object Data Modeling (ODM) library for NodeJS and MongoDB. It gives a straight-forward, schema/pattern based answer for model your application information. It includes query building, validation, built-in typecasting, business logic hooks and lot more, out of the box.

12. What is the working of Mean Stack Architecture?

  • Angularjs being a customer side language in JavaScript so it is the first to process the request made by a customer. 
  • The request at that point enters the Nodejs which is the stage 2 being it the server side language in JavaScript 
  • Then the request enters the phase 3 i.e. Expressjs which makes a request to the database.
  • After these three phases, the data is retrieved and the response is returned to the Expressjs and this work is done by MongoDB.
  • Then in the final step, the data is to be returned back to the AngularJS to display the result and this is done by NodeJS which in return takes the data back from the ExpressJS.

13. How else can the JavaScript code below be written using Node.Js to produce the same output?


setTimeout(function() {


}, 0);






In Node.js version 0.10 or higher, setImmediate(fn) will be used in place of setTimeout(fn,0) since it is faster. As such, the code can be written as follows:






14. Why Is Consistent Style Important And What Tools Can Be Used To Assure It?

Consistent style helps team members modify projects easily without having to get used to a new style every time. Tools that can help include Standard and ESLint.Au

15. How to Update Node (Windows/macOS) Using Installers on

The Node.js downloads page includes binary packages for Windows and macOS — but why make your life more difficult? The pre-made installers — .msi for Windows and .pkg for macOS — make the installation process unbelievably efficient and understandable. Download and run the file, and let the installation wizard take care of the rest. With each downloaded update, the newer versions of Node and npm will replace the older version.

16. What are the timing features of Node.js?

The Timers module in Node.js contains functions that execute code after a set period of time.

setTimeout/clearTimeout – can be used to schedule code execution after a designated amount of milliseconds

setInterval/clearInterval – can be used to execute a block of code multiple times

setImmediate/clearImmediate – will execute code at the end of the current event loop cycle

process.nextTick – used to schedule a callback function to be invoked in the next iteration of the Event Loop

function cb(){

  console.log(‘Processed in next iteration’);



console.log(‘Processed in the first iteration’);


Processed in the first iteration

Processed in next iteration

17. Explain REPL In Node.Js?

REPL stands for “Read Eval Print Loop”. It is a simple program that accepts the commands, evaluates them, and finally prints the results. REPL provides an environment similar to that of Unix/Linux shell or a window console, in which we can enter the command and the system, in turn, responds with the output. REPL performs the following tasks.


It Reads the input from the user, parses it into JavaScript data structure and then stores it in the memory.


It Executes the data structure.


It Prints the result obtained after evaluating the command.


It Loops the above command until the user presses Ctrl+C two times.

18. How To Get a Post Data In Node.Js?

The below code snippet is used to make a Post Request in Node.js.

var request = require(‘request’);


{ form: { key: ‘value’ } },

function (error, response, body) {

if (!error && response.statusCode == 200) {





19.What Is The Difference Between Node.js, Ajax, And Jquery?

The one common trait between Node.js, AJAX, and jQuery is that all of them are the advanced implementation of JavaScript. However, they serve completely different purposes.

Node.Js – It is a server-side platform for developing client-server applications. For example, if we’re to build an online employee management system, then we won’t do it using client-side JS. But the Node.js can certainly do it as it runs on a server similar to Apache, Django not in a browser.

AJAX (Aka Asynchronous Javascript And XML) – It is a client-side scripting technique, primarily designed for rendering the contents of a page without refreshing it. There are a no. of large companies utilizing AJAX such as Facebook and Stack Overflow to display dynamic content.

JQuery –It is a famous JavaScript module which complements AJAX, DOM traversal, looping and so on. This library provides many useful functions to help in JavaScript development. However, it’s not mandatory to use it but as it also manages cross-browser compatibility, so can help you produce highly maintainable web applications.

The Best MEAN Stack Interview Questions

20. Explain Routing In Express.js?

Routing refers to how an application’s endpoints (URIs) respond to client requests. You define routing using methods of the Express app object that correspond to HTTP methods; for example, app.get() to handle GET requests and to handle POST requests.

Below is basic code to handle routing in Express:

var express = require(‘express’)

var app = express()

respond with “hello world” when a GET request is made to the homepage

app.get(‘/’, function (req, res) {

  res.send(‘hello world’)


21. What is DATA Modeling?

Data modeling, in the context of Mongoose and MongoDB, is defining what data can be in a document, and what data must be in a document. When storing user information you might want to be able to save first name, last name, email address, and phone number. But you only need a first name and email address, and the email address must be unique. This information is defined in a schema, which is used as the basis for the data model.

22. What Is Callback Hell?

Initially, you may praise Callback after learning about it. Callback hell is heavily nested callbacks which make the code unreadable and difficult to maintain.

Let’s see the following code example.

downloadPhoto(‘’, displayPhoto)

function displayPhoto (error, photo) {

if (error) console.error(‘Download error!’, error)

else console.log(‘Download finished’, photo)


console.log(‘Download started’)

In this scenario, Node.js first declares the “displayPhoto” function. After that, it calls the “downloadPhoto” function and pass the “displayPhoto” function as its callback. Finally, the code prints ‘Download started’ on the console. The “displayPhoto” will be executed only after “downloadPhoto” completes the execution of all its tasks.

23. What Does Event-driven Programming Mean?

In PC programming, occasion driven writing computer programs is a programming worldview in which the stream of the program is controlled by occasions like messages from different projects or strings. It is an application engineering method separated into two segments.

24. Explain session and cookie in your code?

Cookies and Sessions are used to store information. Cookies are only stored on the client-side machine, while sessions get stored on the client as well as a server. A session creates a file in a temporary directory on the server where registered session variables and their values are stored.

25. What do you understand by services with reference to angular js?

Services in angular js are used to organize and share code across your application. These are the suitable objects which are wired together with the help of dependency injection. The angular js services are lazily instantiated. The service is only instantiated by angular js only when the application component depends on it. In angular js, new services can be made or can even be used in other built-in services. Over 30 built-in services are present in angular js.

26. Why we use mean stack?

It is easy to develop web applications using Node.js because it provides a good variety of JavaScript modules from its humongous library. Mean stack allows the developers to write code in only one language which is JavaScript for both client and server side which makes it a simple and fast language.

27. What type of NoSQL datebase is MongoDb?

MongoDB is a document database.Graph databases are used to store information about networks, such as social connections. Examples include Neo4J and HyperGraphDB. NoSQL databases are rising in popularity as companies apply them to a growing number of use cases.

28. What is a service, and when will you use it?

Angular services are singleton objects which get instantiated only once during the lifetime of an application. They contain methods that maintain data throughout the life of an application, i.e. data does not get refreshed and is available all the time. The main objective of a service is to organize and share business logic, models, or data and functions with different components of an Angular application.

The separation of concerns is the main reason why Angular services came into existence. An Angular service is a stateless object and provides some very useful functions.

29. What’s new in Angular 6 and why shall we upgrade to it?

Angular Elements – Angular Elements is a project that lets you wrap your Angular components as Web Components and embed them in a non-Angular application.

New Rendering Engine: Ivy – increases in speed and decreases in application size.

Tree-shakeable providers – a new, recommended, way to register a provider, directly inside the @Injectable() decorator, using the new providedIn attribute

RxJS 6 – Angular 6 now uses RxJS 6 internally, and requires you to update your application also. RxJS released a library called rxjs-compat, that allows you to bump RxJS to version 6.0 even if you, or one of the libraries you’re using, is still using one of the “old” syntaxes.

ElementRef<T> – in Angular 5.0 or older, is that the said ElementRef had its nativeElement property typed as any. In Angular 6.0, you can now type ElementRef more strictly.

Animations – The polyfill web-animations-js is not necessary anymore for animations in Angular 6.0, except if you are using the AnimationBuilder.

i18n – possibility to have “runtime i18n”, without having to build the application once per locale.

Advanced MEAN Stack Interview Questions and Answers

30. What is AOT?

In computer science, ahead-of-time compilation is the act of compiling a higher-level programming language such as C or C++, or an intermediate representation such as Java bytecode or .NET Framework Common Intermediate Language code, into a native machine code so that the resulting binary file can execute natively. AOT produces machine optimized code, just like a standard native compiler. The difference is that AOT transforms the bytecode of an extant virtual machine (VM) into machine code.

Apps compiled with AOT launch faster for several reasons.

  • Application components execute immediately, without client-side compilation.
  • Templates are embedded as code within their components so there is no client-side request for template files.
  • You don’t download the Angular compiler, which is pretty big on its own.
  • The compiler discards unused Angular directives that a tree-shaking tool can then exclude.

31. Explain the basic rules of CSS Specificity

A linear search looks down a list, one item at a time, without jumping. In complexity terms this is an O(n) search – the time taken to search the list gets bigger at the same rate as the list does.

A binary search is when you start with the middle of a sorted list, and see whether that’s greater than or less than the value you’re looking for, which determines whether the value is in the first or second half of the list. Jump to the half way through the sublist, and compare again etc. In complexity terms this is an O(log n) search – the number of search operations grows more slowly than the list does, because you’re halving the “search space” with each operation.

Comparing the two:

  • Binary search requires the input data to be sorted; linear search doesn’t
  • Binary search requires an ordering comparison; linear search only requires equality comparisons
  • Binary search has complexity O(log n); linear search has complexity O(n)
  • Binary search requires random access to the data; linear search only requires sequential access (this can be very important – it means a linear search can stream data of arbitrary size)

32) What does event-driven programming mean?

In PC programming, occasion driven writing computer programs is a programming worldview in which the stream of the program is controlled by occasions like messages from different projects or strings. It is an application engineering method separated into two segments 1) Event Selection 2) Event Handling

33)What’s a test pyramid? By what method may you complete it while talking about HTTP APIs?

A test pyramid depicts that when works test cases there should be essentially more low-level unit tests than strange state end-to-end tests.

While talking about HTTP APIs, it may come down to this:

  1. A lot of low-level unit tests for your models
  2. Less joining tests, where your test how your models team up with each other
  3. Essentially less affirmation tests, where you test the certifiable HTTP endpoints

33) Features of MEANStack

  • It is designed in order to manage large amounts of data with high scalability and flexibility.
  • MEAN builds extensible applications which are amended for cloud deployment.
  • Streamline deployment is performed with a built-in server.
  • Development of entire application using a single language.

34) MEAN Stack Architecture

MEAN Stack architecture is explained in 5 steps

Step 1: While Client makes a request first,and is handled by AngularJS.

Step 2: Then the request will be passed onto the NodeJS Server called as a parse request.

Step 3: In step3 the ExpressJS will call MongoDB to set the data, the MongoDB retrieves the requested data and returns to ExpressJS.

Step 4: NodeJS will return the requested data to the client.

Step 5: In the final step AngularJS will display the result fetched from MongoDB.

35. What are the Packages required after the installation of Node.js and MongoDB?

Why they are required?

Once Node.js and MongoDB are installed we need some packages via the NPM Package Manager. NPM is a package manager like Nuget, Macports, Ruby Gems etc. It’s possible to search fir and download many 3rd party libraries to use via NPM. NPM will already be installed as part of Node.js.

The required packages are:

  • bower – A package manager for the web. We use NPM for server side node.js modules and Bower manages front-end packages like angular, jquery etc. See the npm bower package for more info.
  • grunt-cli – This is required so that we can run Grunt tasks from the CLI. See the npm grunt-cli package for more info. Grunt is a JavaScript task runner that can be used to automate tasks such as deployment steps, unit testing, linting etc.
  • yo – This is required so that we can run Yeoman generators from the CLI. See the npm yo pacakage page for more info. Yeoman is a plugin that can be run with the ‘yo’ command to scaffold complete projects or useful parts.
  • generator-meanjs – This is the Yeoman generator for Meanjs. We will make use of this to scaffold components of our app, saving us a lot of typing. See the npm generator-meanjs package page for more info.

36) What are the commands that used to run in the terminal to get these packages 

  1. Bower
  2. Grunt-cil
  3. Yo
  4. Generator-mean.js …. ?
  1. npm install -g bower
  2. npm install -g grunt-cli
  3. npm install -g yo
  4. npm install -g [email protected] 

37) What is Inversion of Control?

Inversion of control is a broad term but for a software developer it’s most commonly described as a pattern used for decoupling components and layers in the system.

For example, say your application has a text editor component and you want to provide spell checking. Your standard code would look something like this:

public class TextEditor {

    private SpellChecker checker;

    public TextEditor() {

        this.checker = new SpellChecker();



What we’ve done here creates a dependency between the TextEditor and the SpellChecker. In an IoC scenario we would instead do something like this:

public class TextEditor {

    private IocSpellChecker checker;

    public TextEditor(IocSpellChecker checker) {

        this.checker = checker;



You have inverted control by handing the responsibility of instantiating the spell checker from the TextEditor class to the caller.

SpellChecker sc = new SpellChecker; // dependency

TextEditor textEditor = new TextEditor(sc);

38) What is the difference between Authentication vs Authorization?   check_box_outline_blank

Authentication is the process of ascertaining that somebody really is who he claims to be.

Authorization refers to rules that determine who is allowed to do what. E.g. Adam may be authorized to create and delete databases, while Usama is only authorised to read.

Or in short:

Authentication = login + password (who you are)

Authorization = permissions (what you are allowed to do)


Authentication = Verification

Authorization = Permissions

39)What are Indexes in MongoDB?   check_box_outline_blank

Indexes support the efficient execution of queries in MongoDB. Without indexes, MongoDB must perform a collection scan, i.e. scan every document in a collection, to select those documents that match the query statement. If an appropriate index exists for a query, MongoDB can use the index to limit the number of documents it must inspect.

40)What is SQL injection?   check_box_outline_blank

Injection attacks stem from a lack of strict separation between program instructions (i.e., code) and user-provided (or external) input. This allows an attacker to inject malicious code into a data snippet.

SQL injection is one of the most common types of injection attack. To carry it out, an attacker provides malicious SQL statements through the application.

How to prevent:

  • Prepared statements with parameterized queries
  • Stored procedures
  • Input validation – blacklist validation and whitelist validation
  • Principle of least privilege – Application accounts shouldn’t assign DBA or admin type access onto the database server. This ensures that if an application is compromised, an attacker won’t have the rights to the database through the compromised application.


Mean stack Technology is improving step by step day by day and is likewise simple to use. The main leading mobile application organizations use Mean Stack for creating top versatile applications as Mean Stack is recorded as the best innovation for creating mobile applications.

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