React, also known as React.js, is a highly popular open-source JavaScript library used for building user interfaces in single-page applications and mobile app development. It’s favored for its speed, simplicity, and scalability, offering features like JSX, stateful components, and a virtual Document Object Model (Virtual DOM). JSX is optional but aids in providing helpful error messages. Companies like Facebook and Instagram use React for large and complex online applications, enabling data updates without page refreshes for fast and robust web apps. React is versatile, supporting both simple and complex applications and can be used in the browser and on the server with Node.js. Why choose React over other front-end technologies? React offers a reliable choice with a vibrant community of over 1,400 developers and more than 92,000 websites. Its advantages include a smart diffing algorithm for efficient DOM updates, reusable components for easy app development, and a non-prescriptive approach, allowing a rich library selection. React’s lifecycle methods and React Hooks provide a powerful way to manage component events throughout their lifecycle.