Facebook first released React JS in 2013, and since then, it has become one of the most widely used front-end web development libraries, with a large and active developer community. The library has undergone significant development since its initial release, with new features and updates being released regularly.
In addition to React JS, Facebook has also developed other open-source libraries and tools for front-end web development, such as React Native, which is used for building mobile applications, and Jest, which is used for testing React JS applications.
While Facebook is the primary developer and maintainer of React JS, the library is open-source and can be used and modified by anyone, regardless of their affiliation with Facebook. This means that the library is constantly evolving and improving as developers from around the world contribute to its development.
In conclusion, while Facebook owns and maintains the React JS library, it is available under an open-source license and can be used and modified by anyone. The library has become an essential tool for front-end web development, with a large and active developer community working to improve and enhance its functionality.