joshuakgoldberg/react

React is a JavaScript library for building user interfaces, the buttons, forms, lists, and other elements people interact with on websites and in apps. It helps developers create interactive screens that update smoothly when data changes, without having to manually rewrite the entire page every time something shifts. At its core, the approach is component-based. You build small, self-contained pieces, say, a comment box or a shopping cart button, each managing its own state and behavior. These pieces can then be combined into larger, more complex interfaces. Because each component is written in JavaScript, developers can pass data around freely and keep the interface logic separate from the raw HTML of the page. React handles the work of figuring out what actually changed and updates only the parts of the screen that need it, making the code more predictable and easier to debug. Developers use this tool to build everything from simple websites to large-scale web applications. A startup might use it to build a dashboard, a social media feed, or an onboarding flow. Teams like it because you can adopt it gradually, you don't have to rewrite your entire project to start using it, and you can mix it into existing codebases. It also works beyond the browser: it can render on a server for faster initial page loads, and a companion project called React Native uses the same ideas to build mobile apps for iOS and Android. One notable design choice is the optional JSX syntax, which lets developers write interface markup in a way that looks like HTML but lives inside JavaScript files. It's not required, but most people find it makes the code more readable. The project is open source under an MIT license and actively accepts community contributions.