Hide a reset button (.btn-reset) when no facets are in use

<?php

// Add to your (child) theme's functions.php

add_action( 'wp_head', function() {
?>
    <script>
        (function($) {
            $(document).on('facetwp-loaded', function() {
                var facets_in_use = ('' != FWP.build_query_string());

                // see https://api.jquery.com/toggle/
                // TRUE to show, FALSE to hide
                $('.btn-reset').toggle(facets_in_use);
            });
        })(jQuery);
    </script>
<?php
}, 100 );