FB.getLoginStatus(function(response) {
    statusChangeCallback(response);
});



{
    status: 'connected',
    authResponse: {
        accessToken: '...',
        expiresIn:'...',
        signedRequest:'...',
        userID:'...'
    }
}



<fb:login-button 
  scope="public_profile,email"
  onlogin="checkLoginState();">
</fb:login-button>


function checkLoginState() {
  FB.getLoginStatus(function(response) {
    statusChangeCallback(response);
  });
}