ReactJS, often referred to simply as React, is an open-source JavaScript library primarily used for building user interfaces in web applications. It was developed and is maintained by Facebook and a community of individual developers and companies. React was first released in 2013 and has since gained widespread popularity in the web development community due to its performance, flexibility, and developer-friendly features.Here are some key aspects and features of React:Component-Based Architecture: React is centered around a component-based architecture. In React, you build your user interface by creating reusable components that encapsulate a part of your application's UI. Components can be thought of as building blocks, and they can be composed to create complex user interfaces.