Detect if someone is logged into FB, and the different states

fbdetect.js

 FB.getLoginStatus(function(response) {
                            if(response.session) {
                                fbCheckUserPerms(); //show the FB login
                            } else {
                                // no user session available, someone you dont know
                                if(response.status == "notConnected") {
                                    // But user is logged into facebook
                                    alert("But is logged In"); //show the FB login
                                } else {
                                    // show the default login
                                }
                            }
                        });