From this point on in the chapter, we are going to use React (sometimes referred to as ReactJs), a JavaScript library originally released by Facebook (http://facebook.github.io/react/) and focused on providing a comprehensive set of functions and tools to build the view layer in our applications. React offers a view abstraction focused on the concept of components, where a component could be a button, a form input, a simple container such as an HTML div, or any other element in your user interface. The idea is that you should be able to construct the user interface of your application by just defining and composing highly reusable components with specific responsibilities.
What makes React different from other view implementations for the web is that it is not bound to the DOM by design. In fact, it provides a higher level abstraction called virtual DOM that fits very well with the web but that can also be used in other contexts, for example, building mobile apps, modeling...