React is a JavaScript library widely used as a base in the development of single-page or mobile applications. It is maintained by Facebook and a community of individual developers and companies. However, as of late 2017, key elements of the platform are licensed under the open-source and standard MIT License.
React stands out from earlier JavaScript frameworks in its deep emphasis on componentization. This enables developers to design and think in terms of lightweight, encapsulated modules that are readily reusable. This modularity, coupled with the reactive design pattern of having modules "listen" or subscribe to update events, updating their state and appearance based on these real time triggers has been highly successful.
Two other key components of React include JSX, a JavaScript extension that enables html-like code to be included directly within JavaScript code blocks. Finally, building on lessons of the older Meteor.js framework, React achieves relatively good performance via use of the Virtual DOM.
These advances have been incorporated in the newer Vue.js library. Additionally, the "reactive" design pattern has been widely adopted across many modern platforms. As one example, many iOS apps take advantage of RxSwift, a reactive framework for building Swift apps. Similar libraries exist across many modern development platforms.
