React Introduction

Last Updated : 24 Apr, 2026

ReactJS is a component-based JavaScript library used to build dynamic and interactive user interfaces. It is widely used for creating fast and scalable single-page applications (SPAs).

  • Uses reusable components for better code organization.
  • Improves performance with a virtual DOM.
  • Supports unidirectional data flow for predictable behavior.

"Hello, World!" Program in React

JavaScript 
import React from 'react';

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

export default App;
  • import React from 'react': Imports React to create components and use JSX.
  • function App() { ... }: Defines a functional component called App.
  • return ( ... ): Returns JSX that represents the UI (a div with an h1 tag displaying "Hello, World!").
  • export default App: Exports the App component so it can be used elsewhere.

Working of React

React operates by creating an in-memory virtual DOM rather than directly manipulating the browser’s DOM. It performs necessary manipulations within this virtual representation before applying changes to the actual browser DOM.

  • Actual DOM and Virtual DOM: Initially, there is an Actual DOM(Real DOM) containing a div with two child elements: h1 and h2. React maintains a previous Virtual DOM to track the UI state before any updates.
  • Detecting Changes: When a change occurs (e.g., adding a new h3 element), React generates a New Virtual DOM. React compares the previous Virtual DOM with the New Virtual DOM using a process called reconciliation.
  • Efficient DOM Update: React identifies the differences (this case, the new h3 element). Instead of updating the entire DOM, React updates only the changed part in the New Actual DOM, making the update process more efficient.

Features of React

React is one of the most demanding JavaScript libraries because it is equipped with a ton of features which makes it faster and production-ready. Below are the few features of React.

  • Virtual DOM: React uses a Virtual DOM to optimize UI rendering. Instead of updating the entire real DOM directly,
  • Component-Based Architecture: React follows a component-based approach, where the UI is broken down into reusable components.
  • JSX (JavaScript XML): React uses JSX, a syntax extension that allows developers to write HTML inside JavaScript.
  • One-Way Data Binding: React uses one-way data binding, meaning data flows in a single direction from parent components to child components via props. This provides better control over data and helps maintain predictable behavior.
  • State Management: React manages component state efficiently using the useState hook (for functional components) or this.state (for class components). State allows dynamic updates without reloading the page.
  • React Hooks: Hooks allow functional components to use state and lifecycle features without needing class components.
  • React Router: React provides React Router for managing navigation in single-page applications (SPAs). It enables dynamic routing without requiring full-page reloads.

Applications of React

  • Web Development: React is used to build dynamic and responsive web apps like social media, e-commerce, and blogs platforms.
  • Mobile Apps: React Native helps build iOS and Android apps using a single codebase.
  • Enterprise Applications: Used for large-scale applications that need highly interactive UIs.
  • Dashboards and Data Visualization: Ideal for real-time dashboards and data visualization tools due to high performance.

New Features Added in React 19

  • Server-Side Rendering Improvements: React 19 improves SSR speed, helping apps load faster and boosting SEO.
  • React Suspense Advancements: Better handling of async data for smoother component loading experience.
  • Concurrent Mode Enhancements: Keeps apps responsive and smooth during heavy updates or large data processing.
  • Automatic Batching Enhancements: Groups multiple state updates more efficiently to improve performance.
  • Better Integration with Modern Web Standards: Improved support for Web Vitals, Intersection Observer, and CSS Grid.
  • New Hooks API: New hooks improve state management and lifecycle control in functional components.
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