When people describe React, they often eschew the description of framework-a description often used for something such as Backbone or Angular-in favor of library. The reason for this more lightweight description is that React is not a complete solution for application development. It is often relegated to only a view-layer solution, and that characterization is mostly correct. React has some mechanisms for maintaining internal state, but it has no opinion about or solutions for data flow and management, server communication, routing, or other common frontend application concerns.
React, therefore, is often coupled with some other library or libraries to create a fully fleshed out application. The most common pairing is with an application architecture that is also the brainchild of the wizards at Facebook called Flux. Flux is not a library in and of itself; it is a set of design patterns that have been implemented by many different libraries, which will be discussed in more depth in Chapter 5, Flux and Redux.