ReactJS is JavaScript library used for building reusable UI components. According to React official documentation, following is the definition −React is a library for building composable user interfaces. It encourages the creation of reusable UI components, which present data that changes over time. Lots of people use React as the V in MVC. React abstracts away the DOM from you, offering a simpler programming model and better performance. React can also render on the server using Node, and it can power native apps using React Native. React implements one-way reactive data flow, which reduces the boilerplate and is easier to reason about than traditional data binding.

React Features

JSX − JSX is JavaScript syntax extension. It isn’t necessary to use JSX in React development, but it is recommended.
Components − React is all about components. You need to think of everything as a component. This will help you maintain the code when working on larger scale projects.
Unidirectional data flow and Flux − React implements one-way data flow which makes it easy to reason about your app. Flux is a pattern that helps keeping your data unidirectional.
License − React is licensed under the Facebook Inc. Documentation is licensed under CC BY 4.0.