I think you'd have to be a little more specific in your question about limitations of JS in 2013. There are some 'unsupported' things you can do with jQuery to modify forms and such, but there aren't a lot of limitations per se. I've seen a
number of other questions that you asked on the forums, so perhaps those are the more specific things you are running into?
Proposed as answer byHIMBAPModeratorMonday, March 17, 2014 1:14 AM
I am agree with Chris, you can download
MS CRM 2013 SDK, you will get complete details what you can do which JS and what is considered as support/unsupported.