RJS suitable for doing interactivities within a webpage?

RJS is very good for sending Javascript code back to the browser saying
"Your AJAX is successful and by the way you can update the UI to signal
to the user using the following Javascript I am going to send you."

How about other webpage interactivities, dynamic HTML, is RJS suited for
doing that as well, or is Prototype.js, or jQuery, or plain Javascript
statically loaded with the webpage, still more suited for doing it?

Well stuff like link_to_function, button_to_function etc... do allow
you to supply a block (which yields an RJS page object) rather than a
javascript fragment and there's also the update_page helper which can
turn a block of rjs into actual javascript. I've always thought of RJS
as a bit of a crutch though. It doesn't get too much in your way for
simple stuff like toggle this field or highlight that object but
beyond that it has its limitations. It's awkward to test for example
and fiddly to setup reusable classes or functions. If you need any
substantial amount of javascript I really thing you should bite the
bullet and just get comfortable with javascript (using a library like
jquery or prototype is almost certainly a smart move though)