XMPP strophe, get presence roster

How can I get a the online presence of my "friends" using Strophe lib for JS? Not the roster, even the single presence ( or have I to do 1 req/user in roster? ) Usually I'm notified only at 'presence change' of every resource, but I want to know if a USER is online or offline ( like Pidgin ), without thinking about the many resources logged of each user that can be online simultanealy.

consider all users as offline by default. For all online user resources you get a presence notification automatically. You get all presence changes, and you get the initial after login for all your online contacts.