What is React.js?

React.js (often referred to as React) is a JavaScript library focused on building user interfaces. It is most commonly used for single-page and mobile applications because complex apps usually require additional data libraries. React began at Facebook in 2011, where it was used to help design and develop the front-end aspects of the social network's newsfeed system. In 2013, it was released as open-source content for the community. More recently, Facebook released React Native, an alternate version designed to apply the overall React architecture to native UWP, iOS, and Android applications. React Native is functionally similar to React, but it has different coding techniques for mobile platforms.