ReactJS is an open-source JavaScript library developed by Facebook for building user interfaces, particularly single-page applications where you can build UI components. It’s known for its efficiency, flexibility, and component-based structure.

You can install React with a package manager like npm or yarn. Start a new React project using Create React App: npx create-react-app my-app cd my-app npm start

Components are the building blocks of a React application. They allow you to split the UI into independent, reusable pieces. There are two main types of components: Functional Components: Defined as JavaScript functions. Class Components: Defined using ES6 class syntax.