Js2 auto does not work on emacs

Question

I started using Emacs a couple of weeks ago. I installed js2-mode on emacs and it works like a charm, but now I would like to have autocomplete when working there.

I already installed ac-js2-mode, but when I work in js2 mode, I don’t see the completion at all. Any ideas?

Edit: I set and turned on autofill mode, but when I type a variable, it says the following error in the minibuffer:

"autocomplete error: (void variable ac-source-js2)