The JsHelper in CakePHP 2.x has replaced the AjaxHelper from CakePHP 1.x. I recently tried to implement the JsHelper without very much success; perhaps if I would have read the documentation more closely it would have been quite obvious what my mistake was. So in case you're like me and often skim over long documentation of a helper when you just need one function, in my case: $this->Js->submit() then you can often miss very important information. This article will hopefully help clarify
it.