ReactJS is a frontend JavaScript library used for building user interfaces and create websites.

npm (Node Package Manager) is used to install and manage packages (like React, libraries, tools) in a React project.

Components are the fundamental building blocks of user interfaces in React. They encapsulate reusable pieces of UI logic, markup, and state, allowing developers to break complex applications into smaller, composable parts. This approach promotes modularity, reuse, and maintainability. React components generally fall into two categories: Functional components: These are JavaScript functions that return JSX (or TSX) to describe the UI. They use hooks such as useState and useEffect to manage state and side effects. function Greeting({ name }) { return

Hello, {name}!

; } Class components: An older pattern based on ES6 classes that extend React.Component. They manage state with this.state and rely on lifecycle methods. Class components are less common today due to the widespread adoption of hooks. class Greeting extends React.Component { render() { return

Hello, {this.props.name}!

; } } Components receive data through props, which are immutable inputs passed from parent components, and they manage internal state to support dynamic behavior. React follows a unidirectional data flow: parents pass data down via props, and child components communicate changes upward through callbacks. By composing components (nesting them within one another) developers can build scalable applications, including those that use routing libraries or external state management solutions.