<script>
function control(){
    var $building = $('#gcs_guest_registration_buildingId');
    var $floor = $('#gcs_guest_registration_floorId');
    // When sport gets selected ...
    $('form select').on('change', function(){
      // ... retrieve the corresponding form.
      var $form = $(this).closest('form');
      // Simulate form data, but only include the selected sport value.
      var data = {};
      data[$building.attr('name')] = $building.val();
      data[$floor.attr('name')] = $floor.val();
      //data[$building.attr('name')] = $building.val();
      data['_csrf_token'] = $('#gcs_guest_registration__token').val();

      // Submit data via AJAX to the form's action path.
      $.ajax({
        url : $form.attr('action'),
        type: $form.attr('method'),
        data : data,
        success: function(html) {
            $form.html($(html).find('form'));
            control();
          // Replace current position field ...
          //$('#gcs_guest_registration_floorId').replaceWith(
            // ... with the returned one from the AJAX response.
            //$(html).find('#gcs_guest_registration_floorId')

          // Position field now displays the appropriate positions.
        }
      });
    });
}
control();
</script>