Facebook Connect: User has logged in and given permissions, now what?

So i've been trying to get FB Connect working on my site, simply for login and authentication, using the Javascript SDK and following the code at:

https://developers.facebook.com/docs/guides/web/

So the button appears, i click it, a dialog pops up, i click that, presumably my site now has permission to know who i am...

Then what? The guide goes on to saying all the stuff I can access through the Facebook API, all the cool things about permissions, but presumably i need the user's ID or access token or something to get at this stuff. How is that given to me? left as a attribute on one of the elements? Left in a Javascript variable somewhere? Given as an argument to some callback? Thrown high into the heavens for me to receive via satellite downlink?

This is probably incredibly simple, but for the life of me i have not been able to figure it out. Facebook's tutorials have failed me, and so has Google. I want to get this in the Javascript, so I can immediately fill in form-data using the user's Facebook name, put a picture, etc. etc., and presumably send this all back to the server so the server can validate with Facebook t开发者_如何学Gohat the data is real.

I'm assuming you're using the Login button? https://developers.facebook.com/docs/reference/plugins/login/

If you simply want form info, check out the registration plugin - https://developers.facebook.com/docs/plugins/registration/

However, to answer your question, make an API call to /me. For example:

FB.api('/me', function(user) {
  if(user != null) {
    // The user object now contains info about the logged in user
  }
});

You should subscribe to the auth.login event and wrap the above API call in the successful response, i.e.:

FB.Event.subscribe('auth.login', function() {
  // JS to run if when the user logs in, for example, the code snippet above
});