FB.init.js

window.fbAsyncInit = function () {
  FB.init({ appId: #{APP_ID}, status: true, cookie: true, xfbml: true });

  /* All the events registered */
  FB.Event.subscribe('auth.login', function (response) {
      // do something with response
      alert("login success");
  });
  FB.Event.subscribe('auth.logout', function (response) {
      // do something with response
      alert("logout success");
  });

  FB.getLoginStatus(function (response) {
    if (response.session) {
      // logged in and connected user, someone you know
      alert("login success");
    }
  });
};