ReactJS is an open-source, component based front end library responsible only for the view layer of the application. It is maintained by Facebook.
ReactJS uses virtual DOM based mechanism to fill in data (views) in HTML DOM. The virtual DOM works fast owning to the fact that it only changes individual DOM elements instead of reloading complete DOM every time.
React in itself has a very small API, and you basically need to understand 4 concepts to get started:
A React application is made up of multiple components, each responsible for outputting a small, reusable piece of HTML. Components can be nested within other components to allow complex applications to be built out of simple building blocks. A component may also maintain internal state - for example, a TabList component may store a variable corresponding to the currently open tab.
Its primary goal is to make it easy to reason about an interface and its state at any point in time, by dividing the UI into a collection of components.
