Handle facebook login window close action

Question

I am using openFB for facebook login.

openFB.login(
            function(response) {
                if (response.status === 'connected') {
                    // do something
                } else {
                    console.log('Facebook login failed');
                }
            }
        )

This opens the login window.
How can I handle an event when the user closes this window without signing in?