Grabing a public fb uid

gistfile1.js

var facebook_user_id;
window.fbAsyncInit = function() {
  // init the FB JS SDK
  FB.init({
    appId      : 'YOUR_APP_ID', // App ID from the App Dashboard
    status     : false, // check the login status upon init?
    cookie     : true, // set sessions cookies to allow your server to access the session?
    xfbml      : true  // parse XFBML tags on this page?
  });

  // Additional initialization code such as adding Event Listeners goes here
  FB.getLoginStatus(function(response){
    facebook_user_id = FB.getUserID()
  });
};

// Load the SDK's source Asynchronously
// Note that the debug version is being actively developed and might
// contain some type checks that are overly strict.
// Please report such bugs using the bugs tool.
(function(d, debug){
   var js, id = 'facebook-jssdk', ref = d.getElementsByTagName('script')[0];
   if (d.getElementById(id)) {return;}
   js = d.createElement('script'); js.id = id; js.async = true;
   js.src = "//connect.facebook.net/en_US/all" + (debug ? "/debug" : "") + ".js";
   ref.parentNode.insertBefore(js, ref);
 }(document, false));