Welcome to React.js!

React (also called React.js or ReactJS) is a very popular JavaScript library for building beautiful and fast user interfaces, especially single-page applications (SPAs).

Created and maintained by Facebook (now Meta), released in 2013.

"React is a JavaScript library for building user interfaces"
— Official React website

Why do developers ❤️ React?

#	Reason	Explanation
1	Component-Based Architecture	Build UI as reusable, independent pieces (Header, Card, Button, Footer…)
2	Virtual DOM	Super fast updates — only real DOM changes are applied
3	One-way Data Flow	Makes the app predictable and easier to debug
4	Huge Ecosystem	Redux, React Router, Next.js, Zustand, TanStack Query, MUI, Chakra UI…
5	Works everywhere	Web, Mobile (React Native), Desktop (Electron), VR (React 360)…
6	Best Developer Experience (DX)	Fast refresh, great dev tools, amazing community

Core Concept of React: Components

Think of your UI as LEGO bricks.

function Button() {
  return <button>Click me! </button>
}

function Card() {
  return (
    <div className="card">
      <h2>Amazing Product</h2>
      <p>Best product ever made!</p>
      <Button />
    </div>
  )
}