Introduction to React

What Is React?

React is a JavaScript library for building user interfaces. It is declarative, component-based, and updates efficiently through the Virtual DOM.

Why React?

• Components - Encapsulated, reusable UI pieces.
• Virtual DOM - Minimal real-DOM updates via diffing.
• Ecosystem - Router, Redux, Next.js, React Native.

Virtual DOM vs Real DOM

React renders a lightweight tree, diffs it against the previous tree, and patches only changed nodes in the real DOM.

function Welcome({ name }) {
  return <h1>Hello, {name}!</h1>;
}

Key Points

• React is a UI library, not a full framework.
• Data flows down via props; events flow up.
• JSX compiles to React.createElement calls.