Javascript Common Task Forms Library

I am wondering if someone knows a library with common tasks when manipulating forms, I need some additional tasks, such as conditional selectors that show / hide other fields, clone fields, reset child selectors when the parent selector changes, add parameters to the selectors dynamically etc.

I already have custom functions using jquery to accomplish some of these tasks, but they are not "portable" as I did this for a particular application, and I think there are better ways to do this than what I did.