how to prepare for mern stack interview

How to Prepare for MERN Stack Interview?

Blog Authors | Board Infinity

MERN stack is regarded as one of the most powerful and in-demand web technology stacks in today's marketplace. MERN is a free and open-source JavaScript software stack for building dynamic and interactive websites and web applications. MERN stack is basically based on JavaScript.

What is MERN Stack?

MERN stack is a web development framework. It consists of MongoDB, ExpressJS, ReactJS, and NodeJS as its working components. Here are the details of what each of these components is used for developing a web application when using MERN stack:

  • MongoDB: It is a document-oriented, No-SQL database used to store the application data.
  • NodeJS: It is the JavaScript runtime environment. It is used to run JavaScript on a machine rather than in a browser.
  • ExpressJS: It is a framework layered on top of NodeJS, used to build the backend of a site using NodeJS functions and structures. Since NodeJS was not developed to make websites but rather run JavaScript on a machine, ExpressJS was developed.
  • ReactJS: It is a library created by Facebook. It is used to build UI components that create the user interface of the single page web application.

How to Get a Job as MERN Stack Developer

Step 1: Learning and Enhancing the Knowledge!

  • To understand the various complex concepts, one has to make sure one knows about the fundamentals. JavaScript & HTML/CSS form the base of web development. For any novice, one should be clear about all aspects of these technologies.
  • After learning the fundamentals of web development, one should try to learn the various MERN Stack concepts along with hands-on experience.
  • Test the knowledge by creating test web pages and applying the concepts learned in the course. JavaScript can be found in almost all web applications. Become proficient in its use.
  • Knowledge of programming concepts can help improve coding skills. Some theories/knowledge to acquire before pushing ahead are:
  1. Algorithms and their Formulation
  2. Data Structures (types, properties, and use)
  3. Programming Technologies
  4. Databases and their Management

Step 2: Maintaining an Outstanding MERN-Stack Portfolio

While the resume gives employers an idea about your education, certifications, and skills, an excellent portfolio provides concrete evidence of your abilities and will help you to stand out from the competition. A portfolio is a collection of the best work, and if you want to land a full-stack development job, you’ll have to display a wide range of coding abilities. It should highlight your strengths and skills through projects you’ve accomplished. A portfolio helps your future employers gauge your skills, strengths, and talents.

Step 3: Interview Preparation

During an interview for a MERN Stack developer, the recruiter will want to assess your knowledge and skills along with your interpersonal skills. Below are a few steps to help you prepare for an interview:

  • Ask the recruiter beforehand about the interview format.
  • Revise the basics, especially theoretical knowledge.
  • Don’t be afraid to ask questions if you’re unsure what’s being requested of you.
  • Engage your interviewer with a friendly and confident demeanor.
  • Look at each problem from various angles, and adopt a multifaceted approach to solutions.
  • Brush up on the concepts of data structures and algorithms.

MERN Stack Developer Interview Questions

1. What do you understand by Virtual DOM? Explain it's working.

A virtual DOM is a lightweight JavaScript object which originally is just a copy of the real DOM. It is a node tree that lists the elements, their attributes, and content as objects and their properties. React’s render function creates a node tree out of the React components. It then updates this tree in response to the mutations in the data model which are caused by various actions done by the user or by the system.

  • Whenever any underlying data changes, the entire UI is re-rendered in Virtual DOM representation.
  • Then the difference between the previous DOM representation and the new one is calculated.
  • Once the calculations are done, the real DOM will be updated with only the things that have actually changed.

2. What are the differences between a class component and a functional component?

Class Components

  • Class-based components use ES6 class syntax. It can make use of the lifecycle methods.
  • Class components extend from React component.
  • In here you have to use this keyword to access the props and functions that you declare inside the class components.

Functional Components

  • Functional Components are simpler compared to class-based functions.
  • Functional Components mainly focuses on the UI of the application, not on the behavior.
  • To be more precise these are basically rendered functions in the class component.
  • Functional Components can have state and mimic lifecycle events using Reach Hooks.

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

  • Asynchronous event-driven IO helps concurrent request handling – All APIs of Node.js are asynchronous. This feature means that if a Node receives a request for some Input/Output operation, it will execute that operation in the background and continue with the processing of other requests. Thus it will not wait for the response from the previous requests.
  • Fast in Code execution – Node.js uses the V8 JavaScript runtime engine, the one which is used by Google Chrome. Node has a wrapper over the JavaScript engine which makes the runtime engine much faster and hence the processing of requests within Node.js also becomes faster.
  • Single Threaded but Highly Scalable – Node.js uses a single thread model for event looping. The response from these events may or may not reach the server immediately. However, this does not block other operations. Thus making Node.js highly scalable. Traditional servers create limited threads to handle requests while Node.js creates a single thread that provides service to much larger numbers of such requests.
  • Node.js library uses JavaScript – This is another important aspect of Node.js from the developer’s point of view. The majority of developers are already well-versed in JavaScript. Hence, development in Node.js becomes easier for a developer who knows JavaScript.

4. Explain the advantages of BSON over JSON in MongoDB?

  • BSON is designed to be efficient in space, but in some cases is not much more efficient than JSON. In some cases, BSON uses even more space than JSON. The reason for this is another of the BSON design goals: traversability. BSON adds some "extra" information to documents, like the length of strings and sub-objects. This makes traversal faster.
  • BSON is also designed to be fast to encode and decode. For example, integers are stored as 32 (or 64) bit integers, so they don't need to be parsed to and from the text. This uses more space than JSON for small integers but is much faster to parse.
  • In addition to compactness, BSON adds additional data types unavailable in JSON, notably the BinData and Date data types.

5. If Node.js is single-threaded then how does it handle concurrency?

Node provides a single thread to programmers so that code can be written easily and without a bottleneck. Node internally uses multiple POSIX threads for various I/O operations such as File, DNS, Network calls, etc.

When Node gets an I/O request it creates or uses a thread to perform that I/O operation and once the operation is done, it pushes the result to the event queue. On each such event, the event loop runs and checks the queue and if the execution stack of Node is empty then it adds the queue result to the execution stack. This is how Node manages concurrency.

6. What is JSX in ReactJS?

JSX is a syntax extension to JavaScript and comes with the full power of JavaScript. JSX produces React elements. You can embed any JavaScript expression in JSX by wrapping it in curly braces. After compilation, JSX expressions become regular JavaScript objects. This means that you can use JSX inside of if statements and for loops, assign it to variables, accept it as arguments, and return it from functions.

7. What is prop drilling and how can you avoid it?

When building a React application, there is often the need for a deeply nested component to use data provided by another component that is much higher in the hierarchy. The simplest approach is to simply pass a prop from each component to the next in the hierarchy from the source component to the deeply nested component. This is called prop drilling.

The primary disadvantage of prop drilling is that components that should not otherwise be aware of the data become unnecessarily complicated and are harder to maintain.

To avoid prop drilling, a common approach is to use React context. This allows a "Provider" component that supplies data to be defined and allows nested components to consume context data via either a "Consumer" component or a "useContext" hook.

8. What is the purpose of MongoDB?

MongoDB is a document-oriented database manager designed for storing high volumes of data. It saves data in binary JSON format and implements the concept of collection and documentation. MongoDB is a cross-platform, NoSQL database equipped with high performance, high scalability, and flexibility that allow for seamless querying and indexing.

9. What is the purpose of ExpressJS?

ExpressJS is a web application framework designed to support and host Node.js projects. It is an open-source framework available under the MIT license. ExpressJS manages the workflow between the front-end and the database and facilitates a smooth and secure transfer of data. It boasts of excellent error handling and web design functionality to optimize the web development process.

10. Define Data Modelling?

Data modelling is a term used in the context of Mongoose and MongoDB. As the name suggests, data modelling refers to the process of creating a data model for the data at hand so it can be stored in a database. A data model is a conceptual representation of data objects, the relation among different data objects, and the rules that define those relations.

  • It helps to represent the data visually while also enforcing business rules, regulatory compliances, and government policies on the data.
  • It is implemented to ensure consistency in naming conventions, default values, semantics, security, and quality of the data.

Learning MERN Stack has its advantages when it comes to getting a job in the IT sector. Now, you can be a pro at it too and learn full-stack web development with ease. Enrol in Board Infinity's Full Stack Development course and learn with personalized mentoring from industry experts. Open doors to new career opportunities!

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