Who is a Mern Stack Developer?

A MERN Stack Developer is a talented programmer who focuses on creating web applications with MongoDB, Express, React, and Node.js. These technologies collaborate to develop a site’s front-end (what users see and interact with) and back-end (the server-side logic that runs the application).

List the abbreviation of MERN

MERN in abbreviated form is:

• ExpressJS
• MongoDB
• ReactJS
• NodeJS

What is ReactJS?

ReactJS is a well-liked JavaScript library that is used to create user interfaces for web applications. It assists developers in constructing reusable components, which serve as the foundation for more intricate UI designs. ReactJS is recognized for its effectiveness and employs a virtual DOM to swiftly render components. This library operates on the client side, within the web browser, and utilizes JSX to define UI components.

What are React Hooks?

React Hooks are essentially just functions that allow you to use state and other handy React features within your functional components. These were added in React 16.8 to enable developers to utilize state and lifecycle features in functional components, which were previously only available in class components. Some popular hooks that are widely used include useState, useEffect, and useContext.

Explain the MVC architecture?

The Model-View-Controller (MVC) framework helps organize code for web applications by breaking it into three key components: the Model, the View, and the Controller. Each component plays a distinct role in the application. The Model handles data storage and management, presenting the data in a format that the application can easily interpret.

Explain the building blocks of React?

In React, five key components are essential:

1. Components: These are chunks of code that can be reused and produce HTML output.
2. JSX: This abbreviation means JavaScript and XML, enabling HTML writing in React.
3. Props and State: Similar to function parameters, props and State act like variables.
4. Context: It allows for data to flow through components as props in a hierarchical structure.
5. Virtual DOM: A lighter version of the real DOM, it simplifies DOM manipulation.

What are props in React?

In React, props (which are short for properties) serve as a means of transferring data from a parent component to a child component. They are designed as read-only elements that facilitate communication among different components. Essentially, props are propagated down the component hierarchy, enabling the development of flexible and reusable components.

What are the advantages of ReactJS?

• The Virtual DOM helps boost performance by reducing direct interaction with the real DOM.
• Using a component-based approach promotes modularity and reusability in code.
• Declarative syntax streamlines the writing and comprehension of UI code.
• One-way data binding simplifies data flow management.
• The community and ecosystem around it are large, and active, and offer extensive libraries and support.

What Is Replication In MongoDB?

Replicating data can sometimes improve read performance by spreading read operations across several servers. Storing data copies in multiple data centers can enhance data accessibility and availability for distributed applications. Having extra copies can also be useful for purposes like backup, reporting, and disaster recovery.

How is React different from Angular JS?

• In terms of programming languages, React utilizes JavaScript (or JSX) whereas Angular utilizes TypeScript.
• Regarding structure, React is essentially a library focused on the front-end display, while Angular is a comprehensive MVC framework.
• When it comes to connecting data, React employs one-way data binding, while Angular employs two-way data binding.
• For managing the Document Object Model (DOM), React utilizes a virtual DOM, whereas Angular interacts directly with the actual DOM.
• In terms of complexity for beginners, React is often seen as more accessible to learn compared to Angular.

What in React are Higher-Order Components (HOC)?

A higher-order component (HOC) is like a helper function in React that takes a component as input and creates a new component. It’s called “higher-order” because it builds on the compositional nature of React. These components are known as “pure” because they can work with any child component without changing its behavior. HOC is commonly used for

1. Reusing code, logic, and abstracting common patterns
2. Intercepting component behavior
3. Managing and abstracting component state
4. Modifying component props

What is Reconciliation in React JS?

When changes occur in a component’s props or state, React checks to see if a real update to the DOM is needed. This check involves comparing the new element with the previous one. If they are different, React updates the DOM. This is known as the reconciliation process.

What are the advantages of using React Hooks?

The useState and useEffect functions in React simplify managing component state and lifecycle in functional components. Hooks also promote the reusability of stateful logic in multiple components, reduce boilerplate code, and improve code readability and understanding.

What are the limitations of React?

• Learning Curve: Although React is easy to understand, getting used to the ecosystem and related tools may take some time.
• Overhead: React apps might initially have bigger bundle sizes compared to other frameworks.
• JSX: Certain developers may need time to adjust to the unique syntax of JSX.
• SEO: Extra work may be needed for search engine optimization with React apps.

What are the key features of Node.js?

When handling multiple requests at the same time, Asynchronous I/O allows for efficient processing without blocking. It operates on an event-driven, asynchronous model and utilizes a single-threaded event loop to manage various connections concurrently. Moreover, it is compatible with various platforms such as Windows, Linux, and macOS. Additionally, NPM (Node Package Manager) offers a wide array of open-source libraries and modules to enhance functionality.

What is Sharding in MongoDB?

Sharding is a technique used to spread out data among multiple machines to make data sharing easier. MongoDB uses sharding to assist in managing large data sets and meeting high-performance needs. This allows MongoDB to scale horizontally. In a cluster, MongoDB disperses data among the shards at the collection level.

What distinguishes a class component from a functional component?

Class components and functional components are two primary ways of creating components in React, each with its syntax and features.

1. Syntax:

   • Class components are defined using ES6 classes that extend the React.Component class. They require a render method where the UI is defined.
   • Functional components are simply JavaScript functions that take props as input and return JSX, describing the UI of the component.

2. State Management:

   • Class components can have state managed via the this.state object and are typically used for components that need to manage internal state.
   • Functional components, before React 16.8, couldn’t manage state. With the introduction of hooks, specifically the useState hook, functional components can now manage state just like class components.

3. Lifecycle Methods:

   • Class components have access to lifecycle methods like componentDidMount, componentDidUpdate, etc., which allow developers to run code at specific points in the component’s lifecycle.
   • Functional components, before React 16.8, couldn’t utilize lifecycle methods. With hooks, specifically the useEffect hook, functional components can perform side effects and manage lifecycle behavior.

4. Code Organization:

   • Class components tend to require more boilerplate code, such as constructor functions and binding of event handlers.
   • Functional components are more concise and allow for cleaner, more readable code, especially with the use of hooks.

5. Performance:

   • Class components may have a slight performance overhead due to the way React manages them internally.
   • Functional components, especially with hooks, are optimized for performance and are considered the future of React development.

What do you mean by Asynchronous API?

In web development, asynchronous APIs enable certain tasks to be carried out without pausing the main process. This typically includes sending requests to servers or running code in the background. Methods such as callbacks, promises, or async/await are used in asynchronous APIs to manage these non-blocking operations.

What is Callback Hell and What is the main cause of it?

Have you ever heard of ‘Callback Hell,’ also known as the ‘Pyramid of Doom’? This is when you have multiple nested callbacks that make the code hard to read and manage. It happens when you’re dealing with asynchronous operations using callbacks within callbacks within callbacks, which creates a really deep and indented structure. The primary reason for this is because of how JavaScript handles asynchronous tasks with callbacks, leading to code that is deeply nested and difficult to follow.

What is the purpose of MongoDB?

MongoDB is a database manager that is designed for storing large amounts of data in a document-oriented manner. It uses a binary JSON format and includes collections and documents. MongoDB is a NoSQL database that is known for its high performance, scalability, and flexibility, making querying and indexing operations smooth and efficient.

Explain the event loop in Node JS.

In JavaScript, the event loop helps with asynchronous programming. Even though all operations happen on one thread in JS, we can create the illusion of multithreading using smart data structures. The Event Loop handles asynchronous tasks by queuing and monitoring events.

What is Reconciliation in ReactJS?

When changes occur in a component’s state or props, Reconciliation in React involves updating the DOM to align with the virtual DOM. React’s diffing algorithm efficiently identifies the fewest changes required to update the DOM during this process. This optimization helps enhance performance by reducing unnecessary updates to the actual DOM, leading to more efficient UI updates.

What are node JS streams?

Node.js streams are EventEmitter instances used for handling streaming data, which is useful for managing large files like videos or mp3s over the network. Streams use buffers for temporary storage and come in four main types:

1. Writable streams: Allow data to be written, like `fs.createWriteStream()`.
2. Readable streams: Allow data to be read, like `fs.createReadStream()`.
3. Duplex streams: Both readable and writable, like `net.Socket`.
4. Transform streams: Modify or transform data as it is written and read, like `zlib.createDeflate()`.

What is the purpose of ExpressJS?

ExpressJS is a web application framework designed to make developing and hosting Node.js projects easier. It is an open-source framework under the MIT license. ExpressJS effectively manages communication between the front end and the database, ensuring data transfer is secure and smooth.

What are Node JS buffers?

Buffers are used as temporary memory by streams to hold data until it is used. Different from JavaScript’s Uint8Array, buffers have more uses and are mainly used to represent a set length of bytes. Buffers can handle older encodings like ASCII, utf-8, and are set as fixed memory outside the V8 engine.

What are the data types in MongoDB?

MongoDB can store various data types in its documents, resembling JavaScript objects with key/value pairs like JSON. In addition to the basic key/value structure, MongoDB supports a range of data types such as:

• Null
• Boolean
• Number
• String
• Date
• Regular expression
• Array
• Embedded document
• Object ID
• Binary Data

Why use Express.js over Node.js?

When it comes to backend development, Node.js is often used alongside Express.js to make things easier and more scalable. While Vanilla JavaScript works fine for front-end coding, bigger web applications can benefit from using React or Angular. Building a complete app using just Node.js can result in complicated code, so integrating Node.js with Express.js helps improve speed and simplicity, allowing for the creation of scalable web APIs. This collaboration is evident in popular stacks like MEAN and MERN.

What is REPL In Node JS?

REPL, which stands for “Read Eval Print Loop,” is a simple program that processes commands and shows the results. It aims to create a similar environment to a Unix/Linux shell or Windows console, where users can enter commands and receive outputs. The main functions of REPL are:

• READ – Takes the user input, converts it into a JavaScript data structure, and saves it in memory.
• EVAL – Executes the data structure. PRINT – Displays the result of the command.
• LOOP – Repeats the process above until the user presses Ctrl+C twice.

What is MongoDB?

MongoDB is a NoSQL database that is open-source and written in the C++ language. It utilizes JSON-like documents that can have optional schemas. This allows for easy scalability and makes it a cross-platform, document-oriented database. MongoDB operates on the principles of Collections and Documents and can scale out by incorporating features like secondary indexes, range queries, sorting, aggregations, and geospatial indexes. The development of MongoDB is overseen by MongoDB Inc., and it is licensed under the Server Side Public License (SSPL).

What is meant by “Callback” in Node JS?

A callback is used in programming to handle asynchronous tasks, acting as a response to the completion of a function. In Node.js, callbacks are heavily relied upon to run tasks after specific actions are done. For instance, imagine a function designed to read a file; it starts the file reading operation and then hands over control to allow other instructions to be carried out.

What is a Collection in MongoDB?

In MongoDB, a collection can be compared to a table in a relational database, where each collection contains a set of documents. These documents within a collection can have different structures, giving collections flexible schemas.

What are pure components in the MERN Stack?

The MERN stack includes pure components, which are essentially standard but with a focus on the shouldComponentUpdate method. Pure components mainly handle comparing props and states every time there is a change in either one.

Explain the term “Indexing” in MongoDB.

Indexes are extremely important in MongoDB for speeding up query resolution. They store a condensed portion of the dataset in a way that makes it easy to search through quickly. Indexes keep the values of certain fields organized so that queries can be executed more efficiently.

How does Node JS handle Child Threads?

Node.js, in its simplest form, operates using only one thread. Programmers cannot work with child threads or manage them. While some tasks, such as asynchronous I/O, may create child threads, these processes happen in the background without interrupting the main event loop or running any JavaScript code for the application.

 What are forms in React?

Web applications use React to allow users to engage with them through forms. Forms provide users with a way to input the necessary information and interact with the application. They consist of various components like text fields, buttons, checkboxes, and radio buttons. Forms serve multiple purposes such as user verification, searching, filtering, and indexing.

What are some features of MongoDB?

• Indexing: It assists various secondary indexes and provides unique features for different types of indexing, such as unique, combined, geospatial, and full-text indexing.
• Aggregation: It introduces an aggregation system based on the idea of data processing pipelines.
• Special collection and index types: It supports time-to-live (TTL) collections, which enables effective management of data that should expire at a certain time.
• File storage: It presents a user-friendly protocol for storing large files and their associated metadata.
• Sharding: Sharding entails distributing data across multiple machines.

Explain the lifecycle methods of components.

• When the component is created, getInitialState() is run.
• componentDidMount() is called when the component is displayed on the screen.
• shouldComponentUpdate() is triggered when the component decides if any changes are needed in the DOM.
• componentDidUpdate() happens right after the component is updated.
• component will unmount () is called just before the component is removed from the screen.

What is prop drilling?

Replicating data can sometimes increase the ability to read, as it allows clients to spread out read tasks among different servers. Storing copies of data in multiple data centers can improve data accessibility for distributed applications. Having extra copies of data can also serve various needs like backup, reporting, and disaster recovery.

What is Redux?

Redux is a JavaScript library that is open-source and used for managing the state of applications. React utilizes Redux for creating the user interface. It serves as a reliable container for the state in JavaScript applications and handles the state management for the entire application.

How do you manage packages in your node.js project?

When it comes to managing dependencies, there are different tools available like npm and yarn. These tools provide extensive JavaScript libraries with advanced features for handling environment-specific configurations. To ensure consistency in library versions throughout a project, package.json and package-lock.json files are used. This helps prevent compatibility problems when moving the application to new environments.

What are the components of Redux?

The store is where the application’s current state is stored. Actions provide the data for the store, while reducers define the way the application’s state is updated based on the actions sent to the store.

What is JSX in React JS?

React is a JavaScript extension that allows full access to JavaScript’s features. JSX is used to build React components, letting you include any JavaScript expression by wrapping it in curly braces. Once compiled, JSX expressions become regular JavaScript objects. This means JSX can be stored in variables, passed as arguments, returned from functions, and used in if statements and for loops.

What is a React Router?

React Router is a library for routing within React applications. It allows you to create routes in your React application and is a common topic in React interviews.

Why do we need to React Router?

React is a powerful tool for building single-page web applications. With React, developers can easily create multiple views within a single application by defining multiple routes. This allows for consistent structure and behavior throughout the app.

How to handle routing in Express JS?