I'm not aware of any library that does that nowadays. Even tough this is a possible idea, I must say that I'm not sure if making such library is a good effort.
It would have to provide examples of how to expose your server data to the library, how to calculate deltas, and so on. This would force the developer to change this server side code accordingly to the library's protocol.
This could be great for new apps and websites, but this could be a pain to any existing site, with particular data structure, making the effort to implement this not so much preferable to developing your own Javascript to do that with current data already exposed by the app.
All of these on top of potential security problems would be kinda hard to manage in one generic javascript library.
IMHO this is a great idea to make bundles or plugins to specific ORM based MVC frameworks, for example Ruby on Rails or Django. Since the framework itself has an abstraction to the data structure and many security fixes already bundled together, making a bundle to do that would be much more re-usable and more elegant.