$('#button-submit-login').click(function(){
  if($('#form-login-fields').is(':hidden')){
    $('#button-register').hide();
    $('#form-login-fields').show("slide",{
    direction: "right"
    },1500, fucntion(){
      // callback function goes here
    });
  }
  else{
    $('#form-login').submit();
    return false;
  }
});