réact

React, often referred to as React.js or ReactJS, is a free and open-source front-end JavaScript library for building user interfaces and UI components. It is maintained by Meta (formerly Facebook) and a community of individual developers and companies. React can be used as the foundation for developing single-page applications, as well as mobile applications through frameworks like React Native.

One of React's core principles is its component-based architecture. Developers build UIs by breaking them down into reusable, independent pieces called components. Each component manages its own state and can be composed to create complex user interfaces. React utilizes a virtual DOM (Document Object Model) to optimize rendering performance. Instead of directly manipulating the browser's DOM, React creates an in-memory representation of it. When changes occur, React compares the new virtual DOM with the previous one and calculates the most efficient way to update the actual DOM, minimizing expensive direct manipulations.

React's declarative programming paradigm means developers describe what the UI should look like for a given state, and React takes care of updating the DOM to match that description. This contrasts with imperative programming, where developers specify step-by-step instructions for how to change the UI. React's ecosystem is extensive, with numerous libraries and tools available for routing, state management, and other aspects of web development.