A Product Sub-Category Dropdown

product_brands_dropdown.php

<?php 

/**
 * Shortcode for creating a dropdown for all brands.
 *
 * Doc:
 *   https://codex.wordpress.org/Function_Reference/wp_dropdown_categories
 *
 * Inspiration:
 *   https://developer.wordpress.org/reference/functions/get_categories/
 *   https://gist.github.com/foxinni/2922611
 *
 * Usage:
 *   [product_brands_dropdown]
 *
 */
add_shortcode( 'product_brands_dropdown', 'product_brands_dropdown' );

function product_brands_dropdown( $atts ) {

    $select_id = 'brands-dropdown';

    $args = array(
        'id'              => $select_id,
        'show_option_all' => 'Select Brand',
        'orderby'         => 'Name',
        'order'           => 'ASC',
        'child_of'        => 1724, /* Brands Product Category */
        'show_count'      => true,
        'taxonomy'        => 'product_cat',
        'value_field'     => 'slug'
    );

    ?>

    <script type="text/javascript">
    jQuery(document).ready(function($){
        $('select#<?php echo $select_id; ?>').change(function(){

            if (this.options[this.selectedIndex].text === 'Select Brand') {
                return;
            }

            var slug = this.options[this.selectedIndex].value;
            window.location.href = '<?php echo $url_base; ?>/product-category/brands/' + slug;
        });
    });
    </script>

    <?php

    wp_dropdown_categories( $args );
}

?>