React is a library for building user interfaces. It's great to build highly interactive web applications. It was introduced by Facebook. React is simple, declarative and component based. React uses a virtual DOM and makes use of the latest JavaScript features. You can build your application using vanilla JavaScript or Jsx, a syntactical sugar that makes it easy to express complex components. It is a JavaScript library for building user interfaces. It favors a declarative programming style which makes it easier to reason about your code.