Facebook Login Button - return value

Really quick question that the facebook documentation doesnt seem to answer:

When using the login 开发者_如何学JAVAbutton (javascript) how do you get the following:

Login Success /failure User profile details i..e image, name, email etc?

Thanks in advance

There's an onlogin attribute that you can specify inside the fb:login-button element. You can name a function there. I think it works the same way as the callback from FB.Login from the javascript SDK: FB.Login - Facebook Developers

When you login from login button of facebook then it stores cookies in your system that contains your access token that is also unique. That cookies contains your facebook id also. By this access_token you can get every thing about the user.