React is a library for building user interfaces. It provides a way to create reusable components that describe how a UI should look and what data it should bind to. React takes care of a lot of the rendering work for you so that you can focus on just describing the UI. This makes it easier to write UIs that are more predictable and maintainable.
React uses a Virtual DOM to improve performance. The Virtual DOM is a copy of the actual DOM tree that is kept synced in memory. Whenever there is a change in the state of one of your components, React first updates the Virtual DOM. It then compares the latest version of the Virtual DOM with the previous one and then updates the real DOM by patching only the elements that need to be updated. This means that your app can be rendered much faster than if you were using a regular non-virtual DOM.
React also supports unidirectional data flow, a design pattern that makes your code easy to reason about. The React library was created and is maintained by Meta (formerly Facebook) but it’s open source so anyone can contribute. That means there’s a large community around react that’s constantly improving it and keeping it up to date. It’s a great library for both small and large scale apps and it can even be used to build native Android and iOS applications that feel like they are written in the language of the platform.