Things like React, Flux, Backbone and jQuery (amongst many others) fall into the category of “progressive enhancement”. They’re libraries that bolt on to a server rendered template, and allow it to do things it couldn’t do before. On the surface, this seems great — you add bit and bobs to the good old browser environment, and only use what you need. However, as an ambitious project matures, so does the UI, and it’s requirements. So you reach out and grab another library that does another thing, and then write some ~simple~ code to make library X work nicely with library Y.