FacetWP – give the facet a class name if any of its choices are checked

(function($) {
  $(document).on('facetwp-loaded', function() {
    var facet_name = 'YOUR_FACET_NAME';
    var in_use = FWP.facets[facet_name].length ? true : false;
    $('.facetwp-facet-' + facet_name).toggleClass('has-checked', in_use);
  });
})(jQuery);