React.js Introduction & Key Features Explained (2025)

Introduction – Why Learn React?

In the evolving world of modern web development, building fast, dynamic, and responsive user interfaces is essential. Traditional methods like manipulating the DOM manually or using full-blown frameworks often result in performance bottlenecks and complex code maintenance.

React.js — a powerful open-source JavaScript library developed by Facebook — addresses these challenges with a component-based architecture, virtual DOM, and unidirectional data flow.

In this guide, you’ll learn:

• What React is and why it’s popular
• Core features that set React apart
• Key concepts like JSX, Virtual DOM, and components
• Real-world applications of React in frontend development

What is React?

React is a declarative, efficient, and flexible JavaScript library used for building user interfaces — particularly for single-page applications (SPAs). React handles the view layer of your application and allows developers to create reusable UI components.

React is often referred to as the “V” in MVC” – Model View Controller architecture.

Developed by Facebook, React is actively used in products like Facebook, Instagram, WhatsApp Web, Netflix, and Airbnb.

Key Features of React

Code Example: Hello World in React

import React from 'react';
import ReactDOM from 'react-dom/client';

function App() {
  return <h1>Hello, React World!</h1>;
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<App />);

Explanation:

• App() is a functional component that returns JSX.
• JSX allows us to write HTML-like syntax inside JavaScript.
• ReactDOM.createRoot().render() is used in React 18+ for efficient rendering.

Best Practices

Use Functional Components
Since React 16.8+, functional components with hooks are the recommended standard over class components.

Keep Components Small & Focused
Break your UI into small, reusable components for better maintainability and testing.

Avoid Direct DOM Manipulation
Always let React manage the DOM using its virtual DOM abstraction.

Diagram: React Flow – Virtual DOM in Action

[User Action]
      ↓
[Component State Update]
      ↓
[Virtual DOM Re-render]
      ↓
[Diffing Algorithm]
      ↓
[Efficient DOM Patch]
      ↓
[Updated UI]

Where React Is Used – Real-World Applications

Summary – Recap & Next Steps

React is a fast, declarative, and component-driven JavaScript library ideal for modern UI development.

Key Takeaways:

• React uses a Virtual DOM to boost performance
• It emphasizes reusable components and JSX syntax
• One-way data binding ensures predictability
• Suitable for web and mobile (React Native)

Real-World Relevance:
React powers complex interfaces in Facebook, Instagram, Netflix, and beyond. Mastering React opens doors to frontend roles in top-tier tech companies.

FAQ Section

What is JSX in React?
JSX is a syntax extension that allows writing HTML-like code within JavaScript. It improves readability and lets you describe UI in a declarative way.

const heading = <h1>Hello, JSX!</h1>;

How does Virtual DOM improve performance?
React creates a lightweight copy of the DOM in memory. When changes occur, it calculates the minimal update required and applies it to the real DOM — avoiding full re-renders.

What is the difference between React and Angular?
React is a library focused on UI, whereas Angular is a full-fledged framework. React uses virtual DOM and unidirectional data flow, while Angular uses real DOM and two-way binding.

Can React be used for mobile apps?
Yes! React Native allows you to build native mobile apps for iOS and Android using React.

Is React SEO-friendly?
Out of the box, React is not SEO-friendly due to client-side rendering. However, using Next.js enables server-side rendering and SEO optimizations.