Facebook's JavaScript library for building user interfaces is React. Facebook created React to manage the increasingly complex interfaces of products such as Facebook's news feed, where many parts of a page can change independently.
React was developed internally by software engineer Jordan Walke and was first deployed in Facebook's news feed in 2011. Facebook open-sourced it in 2013, making the library available to developers outside the company. Its central idea is to build interfaces from reusable components, such as buttons, menus, forms, and profile cards, rather than treating an entire webpage as one large script.
React uses a declarative programming model: developers describe what the interface should look like for a given state, and React helps update the displayed result when that state changes. JSX, a syntax extension commonly used with React, lets developers write markup-like elements directly alongside JavaScript logic.
React is a library rather than a complete application framework. Developers often combine it with separate tools for routing, data fetching, and server rendering. Angular, Vue, jQuery, and Svelte are related or competing technologies, but they are not Facebook's interface library. React is now maintained by Meta and the broader open-source community.