Facebook released the React JavaScript library in 2013 for building user interfaces.
React was created at Facebook by Jordan Walke and other engineers to help build interactive interfaces, especially interfaces that changed frequently as data updated. Facebook first used React internally before making it publicly available.
The library introduced a component-based approach in which interfaces are assembled from reusable pieces. React also became known for its virtual DOM concept, which helps manage updates to displayed content. It was initially controversial because its JSX syntax placed markup-like expressions inside JavaScript.
React is sometimes called a framework, but Facebook originally described it as a library. Its release is separate from Facebook’s later open-source work on the machine-learning framework PyTorch and the programming language Hack.