Introduction & Setup (Interview Questions & Answers)

Ques: What is React?

Ans: React is a JavaScript library developed by Facebook (Meta) for building user interfaces, especially single-page applications (SPAs). It helps developers create reusable UI components and efficiently update and render only the necessary parts of the UI using its virtual DOM system.

Ques: Why use React?

Ans: React is popular because it:

• Enables component-based architecture (reusable code).
• Uses a virtual DOM for faster rendering.
• Supports declarative programming (makes UI predictable).
• Works seamlessly with modern tools and frameworks.
• Offers strong community support and ecosystem (Redux, Next.js, etc.).

Ques: Who developed React, and when?

Ans: React was developed by Jordan Walke, a software engineer at Facebook, and was released in 2013. It was later open-sourced and is now maintained by Meta and the open-source community.

Ques: What are the key features of React?

• JSX (JavaScript XML) syntax
• Virtual DOM for performance optimization
• Component-based architecture
• Unidirectional data flow
• Declarative UI design
• React Hooks (for state & lifecycle in functional components)

Ques: What is the architecture of a React application?

Ans: React follows a component-based architecture:

• View Layer (UI): Built using React components.

• Data Layer (State Management): Managed using hooks, Context API, or external libraries like Redux.

• Logic Layer: Handles user interactions and application logic.

  This architecture separates UI, logic, and data for better maintainability.

Ques: What are React components?

Ans: Components are independent, reusable building blocks of a React application.

They can be of two types:

• Functional Components: Simple JavaScript functions that return JSX.
• Class Components: ES6 classes extending React.Component, including lifecycle methods.

Ques: What is JSX in React?

Ans: JSX stands for JavaScript XML. It allows you to write HTML-like syntax inside JavaScript.

Example:

const element = <h1>Hello, React!</h1>;

Ques: What is Babel and why is it used in React?

Ans: Babel is a JavaScript compiler that converts JSX and ES6+ code into browser-compatible JavaScript.

React relies on Babel to transform modern syntax and JSX into plain JavaScript code that all browsers can understand.

Ques: What is a Virtual DOM, and how does it work?

Ans: The Virtual DOM is a lightweight copy of the real DOM.

When the state of a React component changes:

1. React updates the virtual DOM.
2. It compares the new virtual DOM with the previous version (diffing algorithm).
3. Only the changed parts are updated in the real DOM (reconciliation process).

This makes React faster and more efficient.

Ques: How do you set up a React environment?

Ans: You can set up a React environment in several ways:

1. Using Create React App (CRA):

   npx create-react-app my-app
   cd my-app
   npm start
   

2. Using Vite (faster alternative):

   npm create vite@latest my-app -- --template react
   npm install
   npm run dev
   

3. Manual setup: Using bundlers like Webpack and Babel.

Ques: What is the folder structure of a React project?

Ans: Typical CRA folder structure:

my-app/
│
├── node_modules/
├── public/
│   ├── index.html
│
├── src/
│   ├── App.js
│   ├── index.js
│   ├── components/
│   ├── assets/
│   └── styles/
│
├── package.json
└── README.md

Ques: What is React ES6 Essentials?

Ans: React heavily uses ES6+ features, including:

• Arrow functions → concise syntax
• Classes → for class components
• Destructuring → simplify props/state access
• Modules (import/export) → component sharing
• Template literals → dynamic strings
• Spread/rest operators → simplify object & array handling

Ques: What is React Upgrade, and why is it important?

Ans: React versions introduce performance improvements, new features (like Hooks), and bug fixes.

To upgrade:

npm install react@latest react-dom@latest

Ques: What are some tools used with React development?

• Node.js & npm/yarn → package management
• Babel & Webpack → code compilation and bundling
• React Developer Tools → browser debugging
• ESLint & Prettier → code quality
• VS Code → development environment

Ques: What is the difference between React and other frameworks (like Angular or Vue)?

Feature	React	Angular	Vue
Type	Library	Framework	Framework
Language	JavaScript	TypeScript	JavaScript
Data Flow	One-way	Two-way	Two-way
DOM	Virtual DOM	Real DOM	Virtual DOM
Learning Curve	Easy	Steep	Moderate