React is a free JavaScript library developed by Facebook since 2013. The main purpose of this library is to facilitate the creation of a single-page web application, via the creation of components depending on a state and generating a page (or portion) HTML with each state change.

React is a library that only manages the interface of the application, considered as the view in the MVC model. It can thus be used with another library or an MVC framework like AngularJS. The library stands out from its competitors by its flexibility and performance, working with a virtual DOM and only updating the rendering in the browser when necessary.

The library is used by Netflix (server side only since October 25, 2017 to gain 50% performance4), Yahoo, Airbnb, Sony, Atlassian as well as by the Facebook teams, applying dogfooding on the eponymous social network, Instagram or even WhatsApp. At the end of 2015, announced Gutenberg, an interface for WordPress site editors, developed in JavaScript with Node.js and React.