MEAN Stack Interview Questions

17 December, 2020


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Mean Stack Interview Question and Answers

If you are looking for Mean Stack interview Questions and answers for freshers and experienced, then you are at the right place? Our experts listed out Top 30 frequent Mean stack Interview Questions.

There is a massive demand for Mean Stack Developers with an average salary package of $56K, which is around 2.5 times more than the country's median wage. So you have wonderful opportunities to gear up in your career in JavaScript. Mindmajix Advanced MEAN Stack Interview Questions helps you to crack and acquire your dream job as a Mean Stack Developer. 

Mean Stack Interview Questions for Freshers

1Q) What’s the MEAN Stack?

Ans: The term MEAN stack refers to a collection of JavaScript-based technologies used to develop web applications. MEAN is an acronym for MongoDB, ExpressJS, AngularJS, and Node.js. From client to server to database, MEAN is full-stack JavaScript.

2Q) What is Express?

Ans: Express is one of the most prevalent and generally utilized web systems in the Node.js advancement zone. Express is a negligible web server based on Node.js that gives all the basic usefulness required for conveying web applications to the program and cell phones. ExpressJS enables you to deal with Routes, Server, and I/O stuff effortlessly.

3Q) What is DATA Modeling?

Ans: 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 the 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.

4Q) What are the features of Node.js?

Ans: Node.js is a single-threaded but highly scalable system that utilizes JavaScript as its scripting language. It uses asynchronous, event-driven I/O instead of separate processes or threads. It is able to achieve high output via a single-threaded event loop and non-blocking I/O.

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5Q) Why is consistent style important and what tools can be used to assure it?

Ans: 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.

6Q) What is the difference between AngularJS and Node.js?

Ans: Angular.JS is a web application development framework while Node.js is a runtime system.

7Q) What Are The Key Features Of Node.Js?


Asynchronous event-driven IO helps concurrent request handling – All APIs of Node.js are offbeat. This component implies that if a Node gets a demand for some Input/Output activity, it will execute that task out of sight and proceed with the preparation of different solicitations. Accordingly, it won't sit tight for the reaction from the past solicitations.

Quick in Code execution – Node.js utilizes the V8 JavaScript Runtime motor, the one which is utilized by Google Chrome. Hub has a wrapper over the JavaScript motor which makes the runtime motor substantially quicker and thus preparing of solicitations inside Node.js additionally turns out to be speedier.

Single-Threaded yet Highly Scalable – Node.js utilizes a solitary string model for occasion circling. The reaction from these occasions could conceivably achieve the server quickly. In any case, this does not piece different activities. This way making Node.js exceptionally adaptable. Customary servers make restricted strings to deal with demands while Node.js makes a solitary string that gives administration to significantly bigger quantities of such demands.

Node.js library uses JavaScript – This is another essential part of Node.js from the engineer's perspective. The larger part of engineers is now knowledgeable in JavaScript. Consequently, advancement in Node.js winds up plainly less demanding for a designer who knows JavaScript.

There is an active and energetic group for the Node.js system – The dynamic group dependably keeps the structure refreshed with the most recent patterns in web advancement.

No Buffering – Node.js applications never support any information. They essentially yield the information in pieces.

8Q) Explain REPL In Node.Js?

Ans: The 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 a 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.

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

EVAL- It Executes the data structure.

PRINT- It Prints the result obtained after evaluating the command.

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

9Q) What Is The Difference Between Nodejs, AJAX, And JQuery?

Ans: 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 that 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.

10Q) What's the difference between operational and programmer errors?


  • Operation errors are not bugs, but problems with the system, like request timeout or hardware failure.
  • On the other hand programmer errors are actual bugs.

11Q) What's a test pyramid? How might you actualize it when discussing HTTP APIs?

Ans: A test pyramid portrays that when works test cases there ought to be significantly more low-level unit tests than abnormal state end-to-end tests.

When discussing HTTP APIs, it might come down to this:

  • Plenty of low-level unit tests for your models
  • Less joining tests, where your test how your models collaborate with each other
  • Significantly fewer acknowledgment tests, where you test the genuine HTTP endpoints

12Q) What does event-driven programming mean?

Ans: 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

13Q) Is Node.Js Entirely Based On A Single-Thread?

Ans: Yes, it’s true that Node.js processes all requests on a single thread. But it’s just a part of the theory behind Node.js design. In fact, more than the single thread mechanism, it makes use of events and callbacks to handle a large no. of requests asynchronously.

Moreover, Node.js has an optimized design that utilizes both JavaScript and C++ to guarantee maximum performance. JavaScript executes at the server-side by Google Chrome v8 engine. And the C++ lib UV library takes care of the non-sequential I/O via background workers.

To explain it practically, let’s assume there are 100s of requests lined up in the Node.js queue. As per the design, the main thread of the Node.js event loop will receive all of them and forward them to background workers for execution. Once the workers finish processing requests, the registered callbacks get notified on the event loop thread to pass the result back to the user.

14Q) Explain about MongoDB?

Ans: MongoDB is a document-oriented database that is intended for storing large volumes of information. It saves information in binary JSON form and executes the idea of documentation and collection. MongoDB is a cross-platform, NoSQL database with flexibility, high-performance, and high scalability that allows seamless indexing and querying.

15Q) Explain about ExpressJS?

Ans: ExpressJS is a web application framework intended to host and support Node.js applications. It is an open-source framework accessible under MIT license. ExpressJS runs the work-flow between the database and front-end and helps to exchange smooth and secure data. It boasts of web design functionalities and error handlings to optimize the web development procedure.

16Q) Explain about NodeJs?

Ans: Node.JS is an open-source, single-threat, and cross-platform JavaScript framework utilized to create networking and server-side applications. NodeJs acts as a spine of the MEAN stack. Aside from JavaScript, Node.js uses C++ and C programming languages. Node.js provides an integrated web server that helps to deploy MongoDB databases and its cloud application.

17Q) Explain about AngularJs?

Ans: AngularJS is an open-source front-end web application framework that is maintained by Google. It permits Web Developers to utilize HTML as their layout language and extend HTML syntax to render a web application's elements accurately.

18Q) List out a few IDEs that are commonly used for NodeJs Development?

Ans: Following are the most popular IDEs that are commonly used for NodeJs Development:

  • Cloud9
  • Eclipse
  • Atom
  • Komodo IDE
  • JetBrains IntelliJ IDEA
  • JetBrainsWebStorm

Mean Stack Interview Questions for Experienced

19Q) Justify when to use NodeJs?

Ans: It's ideal to utilize Node.js for creating event-based or streaming period applications that need less C.P.U. Usage of NodesJs: 

Chat Applications.  
Game Servers

1. Good for a Cooperative atmosphere:
 a) NodesJs provides an appropriate environment for numerous people to work along. For example, they post their files; modify documents/files them, check-out, and arrive at those files/documents.
 b) Node.js supports such things by creating a loop for every amended record/file. The "event loop" characteristic of Node.js allows it to deal with numerous events simultaneously while not getting blocked.

2. Servers dedicated for an advertisement:
NodeJS has servers consecrated for handling a large number of requests, which can be utilized for downloading the ads from the focal host, and the ideal responses for taking care of these undertakings are Node.JS.

3. Servers are dedicated to streaming:

Another ideal circumstance to utilize Node.js is the multimedia framework streaming servers place a request to the server, which is used to transfer various multimedia systems.
Summing up the entire, utilizing Node.js is a keen choice, after you need elevated levels of concurrency, be that as it may, less amount of committed C.P.U. Time.
Last anyway, not the littlest sum, since Node.js utilizes JavaScript internally, subsequently it fits best for building client-side applications that moreover use JavaScript.

20Q) When NodeJs Should Not Be Used?

Ans: Node.js can be utilized for the spread of uses. Be that as it may, it's one rib system. Like this, we shouldn't use it for cases any place the apparatus needs a long span. If the worker is playing out some estimation, it won't be permitted to technique different solicitations. In this way, Node.js is an ideal alternative once a cycle that needs less devoted C.P.U. time.

21Q) Explain about Mongoose?

Ans: Mongoose is an Object Document Mapper (ODM), which implies that by utilizing Mongoose, you can characterize objects with a specific outline that can be additionally planned to a MongoDB record/document. It offers a schema-based explanation for demonstrating application information. Mongoose accompanies validation, business logic-hooks, query building, built-in typecasting, and many more features.

22Q) Explain the scope in Javascript?

Ans: In JavaScript, each role has a scope, an assortment of factors and rules characterizing how their remarkable name gets to those factors. You can get to a capacity's perused factors just through the code inside that work. While elements in a specific extension must have novel names, a degree can exist inside another degree. For this situation, the code of the most in-depth extension can get to the factors contained in both of the degrees.

23Q) Differentiate between linear search and binary search?


  • A straight pursuit thinks about the elite thing's individual without bouncing arrangements. Along these lines, regarding intricacy, it orders as an O(n) search wherein the time taken to look through the rundown expands relative to the expansion in the rundown. As opposed to this, a parallel inquiry begins in the elite. This pursuit intends to see whether the thing esteem is more prominent than or not precisely the ideal worth. 
  • This further decides the rundown incentive – regardless of whether it will be in the initial segment or the second piece of the rundown. As far as multifaceted nature, it groups as an O(log n) search where the quantity of search activities generally develops gradually than the rundown. This is chiefly because the inquiry space is broken into half in every action. 
  • While parallel pursuit expects you to initially sort the info information, a straight rundown doesn't have any such requirements.

24Q) Is Node.Js is based on a single thread?

Ans: Indeed, Node.js can be entirely founded on a solitary string. In any case, you should be very much aware that it is only a hypothesis behind Node.Js' plan of Node.Js. Aside from being associated with a single string system cycle, it likewise utilizes callbacks and occasions to oblige an enormous number of requests. It is additionally indispensable for you to take note that Node.Js has an advanced plan. This smoothed-out plan permits it to utilize both C++ and JavaScript, bringing about the most effective execution. The JavaScript gets executed along the edge of the worker. Then again, the C++ library guarantees the preparation of non-consecutive I/O with the assistance of foundation laborers.

25Q) Give a brief explanation of the working mechanism of Node.Js?

Ans: It is intriguing to note that a Node.Js application encourages the making of a solitary string when it is actuated. At whatever point the Node.Js gets a solicitation, it initially finishes the handling before moving onto the following solicitation preparation. It is likewise imperative to refer to here that Node.Js works by utilizing the occasion circle. It also operates to get back to capacities and handles various solicitations that are coming from the client. In the working system of Node.Js, an occasion circle constantly assumes a primary job. An occasion circle is otherwise called a capacity that impels all the occasion controllers. Thus, heaps of works are done toward the back. It is also critical to note that while preparing a solicitation, Node.Js ordinarily appends a get back to work. When the reaction is ready, the occasion triggers the callback capacity to send the response to the client's inquiries

26Q) Explain callback in Node.Js?

Ans: In node.js, the callback activity is utilized to address various server requests. Like, on the off chance that you have a huge record that sets aside effort for a worker to peruse and don't need a worker to peruse that large volume document, the callback is utilized when different solicitations are tended to. Get back to permit the worker to initially deal with the forthcoming solicitation and call up a capacity after the solicitation has been finished. 

For instance, on the off chance that we have a document understood capacity, Node.js naturally restores the control to the execution climate after it begins perusing the record to execute the following guidance. When the document's reading activity is finished, the callback work is called, and the record's substance is passed as its contention. This element makes Node.js exceptionally versatile; with it, an enormous number of questions are prepared without trusting that any component will restore the expected outcome.

27Q) Explain about scope Javascript?

Ans: In JavaScript, each function has a range, basically an assortment of factors and rules characterizing how their exceptional name gets to those factors. You can get a function’s scope variables just through the code inside that work. While variables in a specific scope should have various names, an extension can exist inside another scope. For this situation, the most in-depth scope code can get to the variables.

28Q) Explain about dependency Injection?


  • Dependency Injection is a software system concept that permits you to utilize or infuse a service so that it is self-governing of any client utilization. Thus, you keep the customer from amending the dependencies when the essential service changes. 
  • The main role of dependency injection is to isolate the formation of customers' conditions from their conduct, allowing you to configure approximately coupled projects. In an around associated program, the segments ordinarily burn-through usefulness characterized by interfaces without having any earlier information on which usage classes are being utilized. 
  • Dependency injection permits you to change or change an application's conduct by adjusting the parts that execute the interfaces characterizing an application's highlights.

29Q) Define Event emitters of Node.Js?

Ans: The event module present in the Node.Js would permit you to make and oversee custom events. In this unique circumstance, note that the event module contains the class of game producers that can be utilized to deal with and raise custom events. You ought to likewise know about the way that when an event producer goes over a mistake, it usually discharges a blunder event. Then again, when another client gets added, it conveys a show by another client's name. Additionally, when the new client gets taken out, it sends a performance by the distant client's name.

30Q) Explain about NPM of node.Js?

Ans: The full form of NPM is the Node Package Manager. It is related to the two principal functionalities which are recorded underneath:
 a) It typically functions as an order line utility to introduce the bundles. It additionally does form the executives and relies on the board of different Node.Js bundles.
 b) It likewise fills in as an online archive on account of Node.Js bundles. These are likewise present in the .organization record of Node.Js.
Aside from the inquiries referenced above, consistently consider the multi-center foundation of Node.Js engineering. You likewise need to consider the callback overseer with the goal that you can dominate in the meeting.

31Q) Tell me about Containerization?

Ans: Containerisation is an option in contrast to customary hypervisor-based machine virtualization, including the epitome of an application in a compartment inside its working climate. In containerization, rather than cloning an operational framework for individual virtual machines, it is shared by the various containers. By stacking an application in a virtual machine, you can run the application on any actual appropriate device without stressing over conditions.

32Q) Explain the test pyramid and how can you actualize a test pyramid when discussing HTTP APIs?

Ans: Typically, full-stack web applications are vast and complex. They are intended to extend their functionalities to serve many various necessities of millions of clients. Subsequently, as the size of a full-stack codebase and the number of clients develop, the expense of managing bugs likewise heightens. This, notwithstanding, can be effectively moderated by applying the test pyramid's idea to your codebase.

The test pyramid approach suggests an extreme perspective regarding how various types of robotized tests can and should be utilized to make a decent portfolio. It underscores that the number of low-level UnitTests should be significantly more than elevated BroadStackTests going through a GUI.

While talking about HTTP APIs, you can realize a test pyramid by following the means referenced beneath:
 a) Consolidate a lot of low-level unit tests for your model.
 b) Incorporate less joining tests utilized for deciding how your models team up with one another.
 c) Incorporate fewer affirmation tests utilized for testing certified HTTP endpoints.

33Q) Differentiate the interfaces and classes in typescript?

Ans: Classes and interfaces are structures that advance both articles arranged programming and type-checking in TypeScript. While a class is an outline from which you can gather pieces with a similar arrangement (properties and strategies), an interface gathers related properties and techniques that portray an item. Be that as it may, an interface doesn't give usage or introduction to things. 

Ordinarily, a class characterizes what an article ought to resemble and act like. In like manner, it makes and executes a diagram by instating the class properties and illustrating strategies. Classes are available all through all the periods of a code. An interface, then again, is a virtual structure that exists just inside the setting of TypeScript. The TypeScript compiler utilizes interfaces only for type-checking.

34Q) What is the purpose of an index server in MongoDB?

Ans: In MongoDB, lists are utilized to help and encourage the effective execution of questions. Without files, MongoDB needs to play out an assortment filter wherein it needs to check each report in an assortment and select the fitting archives that coordinate the inquiry explanation. Nonetheless, if each inquiry has a suitable file relegated to it, MongoDB can utilize the list to restrict the number of reports it needs to assess.

35Q)  Explain about Cross-Site Scripting(XSS)?

Ans: Cross-Site Scripting (XSS) is a client-side code infusion assault wherein the vindictive contents are executed in an internet browser by remembering destructive code for an authentic website page or web application. It can likewise happen when an individual taps on untrusted joins that can pass treats and other touchy data to aggressors.
The assault happens when you visit a page or a web application that executes a malevolent code. Consequently, the page or web application turns into a vehicle to convey malignant contents to a client's program. The most generally utilized vehicles for cross-website scripting assaults are gatherings, message sheets, and even site pages that urge clients to remark.

36Q) Explain about AOT and its benefits?

Ans: Angular applications contain HTML layouts close by the standard parts. Since the program can't comprehensively comprehend these parts and HTML layouts, Angular applications should be gathered first before running them in a program.
The Angular early (AOT) compiler changes the Angular HTML and TypeScript code into JavaScript code during the fabricate stage before the program can download and run the code. By incorporating the Angular application in the construction stage, you empower the quicker dispatch of Angular applications in the program.
The advantages of utilizing an AOT compiler are:
a) By utilizing AOT, the program can download a pre-arranged form of the application. The program downloads executable code to promptly deliver the Angular application without sitting tight for the application to gather first. >>Because of AOT, the compiler inlines outside HTML layouts and CSS templates inside the application JavaScript, in this manner dispensing with discrete AJAX demands for source documents.
b) During the assemble stage itself, the AOT compiler identifies and reports any format restricting mistakes.
c) Since AOT incorporates HTML layouts and segments into JavaScript documents before serving them to customers, there are no more formats to peruse and even no hazardous client-side HTML/JavaScript assessment. This lessens the conceivable outcomes of infusion assaults.

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