FacetWP – pre-select a sort option

<?php

add_filter( 'facetwp_preload_url_vars', function( $url_vars ) {
    if ( 'tilbudtest' == FWP()->helper->get_uri() ) {
        if ( empty( $url_vars['sort'] ) ) {
            $url_vars['sort'] = 'on_sale';
        }
    }
    return $url_vars;
} );