React, also known as ReactJS or React.js, is a free and open-source front-end JavaScript library designed to streamline the creation of user interfaces based on reusable components. Maintained by Meta (formerly Facebook) and a community of developers and companies, React is used by an estimated 6% of all websites. According to the 2025 Stack Overflow Developer Survey, it stands as one of the most commonly used web technologies.
One of React's key features is its use of a virtual DOM, an in-memory data structure that allows for efficient updates to the browser's DOM. When components are rendered, React compares the result with the virtual DOM and only updates the actual DOM elements that have changed, a process called reconciliation. This selective rendering provides a significant performance boost. React can be used to develop single-page, mobile, or server-rendered applications with frameworks like Next.js and React Router. React applications often rely on libraries for routing and other client-side functionality because React is primarily focused on user interface and rendering components.
React also offers a profiler tool which measures how many times the React application is rendered and how much time the components take to be rendered. The React DevTools, available as a browser extension, includes profiling capabilities to identify performance bottlenecks. Recent updates include React Native 0.84, which now defaults to Hermes V1 on iOS and Android, enhancing performance and reducing memory usage.
