IMHO the most important "clean code" boundary for web apps is a non-enhanced interface (plain old forms). From there, pages can progressively enhance until the

IMHO the most important "clean code" boundary for web apps is a non-enhanced interface (plain old forms). From there, pages can progressively enhance until the cows come home with jquery plugins and complicated interface code, but as long as you know it boils down to a form submission, it's easy to understand what is going on in the application. The form is the model into your web app, and everything else is just sugar. And whether working on an android app, a QT application in C++ or a jquery based rich client interface, rich client functionality is always somewhat messy in my experience by nature of having many complex interactions in a stateful environment. I certainly don't see using YUI as a silver bullet to alleviate the complexity. As long as it is always clear where the boundaries between the communication between the client code and the server / and its model, you will maintain a clean and maintainable core. If you want to ditch the idea of progressive enhancement and work directly with a web api to your server, then similar rules apply; as long as it is clear that "this page / widget presents a snazzy interface to update this model" you can remain sane in the organization of your app. Finally, if you have a super rich interface like Asana, pivotal tracker or google wave where the entire page is presenting many models at once in many forms, then a functional reactive approach may help, using something like backbone or what luna script promises to be. But using a framework like that has its own cost and complexity and IMO is overkill for many of the web apps out there.