[caprisun]

I've used it in every javascript involved project i've done just because i thought it was always required. is it really required? and what does it do?

[freelancr]

It's not a requirement, it just makes life easier if you have a lot of JavaScript to write.

[Synook]

It is a framework - it abstracts the core applications of JavaScript (e.g. animation, AJAX, form validation) into simple interfaces that can then be used without actual competency in the underlying processes, resulting in a scripting environment that is simpler, easier to use and faster to work with (i.e. "write less, do more").

But no, it is not a requirement, just a convenience. It is good to try working with basic prototype-style JavaScript using the core functions for a while, so you know what is actually going on behind the scenes.

[Shiro]

How can you have used it in every project without knowing what it is? For that matter, how can you have even learned it without finding out what it was along the way?