React is a JavaScript library for building user interfaces, developed by Meta (Facebook). It's the most popular frontend framework, used by millions of websites and applications worldwide.
Core Concept: Components
React applications are built from components, self-contained pieces of UI that manage their own logic and appearance:
function WelcomeMessage({ name }) {
return <h1>Hello, {name}!</h1>;
}
Components can be combined to build complex interfaces while keeping code organized and reusable.
Key Features
JSX
React uses JSX, a syntax that lets you write HTML-like code in JavaScript:
const element = <button onClick={handleClick}>Click me</button>;
Virtual DOM
React maintains a virtual representation of the UI. When data changes, it calculates the minimum DOM updates needed, making updates fast and efficient.
One-Way Data Flow
Data flows down through components via "props." This makes applications predictable and easier to debug.
Hooks
Modern React uses hooks for state and side effects:
- useState: Manage component state
- useEffect: Handle side effects (API calls, subscriptions)
- useContext: Share data across components
React Ecosystem
- Next.js: Full-stack React framework with routing and server-side rendering
- Redux/Zustand: State management for complex applications
- React Router: Client-side routing
- React Query: Data fetching and caching
- Tailwind CSS: Popular styling approach
Why React is Popular
- Large ecosystem: Thousands of packages and tools
- Job market: Most in-demand frontend skill
- Flexibility: Library, not a framework. Use what you need
- Community: Massive community, lots of learning resources
- Meta backing: Continued investment and development