Заполните второй раскрывающийся список с помощью Selectize

Я использовал плагин Chosen для заполнения второго выпадающего списка, основанного на выборе первого. Я хотел бы перейти на плагин Selectize по соображениям производительности сейчас, но у меня возникли проблемы с этим. Моя установка выглядит следующим образом:

1-й выпадающий список = Пользовательский тип сообщения (тип)

2-й выпадающий = Таксономия (местоположение)

В моем файле functions.php у меня есть следующее:

// SECOND DROPDOWN

function my_dropdown_categories( $taxonomy, $current_selected = '', $include = null ) {
// Get all terms of the chosen taxonomy
$terms = get_terms($taxonomy, array('orderby' => 'name'));

// our content variable
$list_of_terms = '<select id="location"  class="selectboxSingle" name="location">';

if ( ! is_wp_error( $terms ) ) foreach($terms as $term){

// If include array set, exclude unless in array.
if ( is_array( $include ) && ! in_array( $term->slug, $include ) ) continue;

$select = ($current_selected == $term->slug) ? "selected" : ""; // Note: ==

if ($term->parent == 0 ) {

// get children of current parent.
$tchildren = get_term_children($term->term_id, $taxonomy);

$children = array();
foreach ($tchildren as $child) {
$cterm = get_term_by( 'id', $child, $taxonomy );
// If include array set, exclude unless in array.
if ( is_array( $include ) && ! in_array( $cterm->slug, $include ) ) continue;
$children[$cterm->name] = $cterm;
}
ksort($children);

// OPTGROUP FOR PARENTS
if (count($children) > 0 ) {
//     $list_of_terms .= '<optgroup label="'. $term->name .'">';
if ($term->count > 0)
$list_of_terms .= '<option class ="group-result" value="'.$term->slug.'" '.$select.'>' . $term->name .' </option>';
} else
$list_of_terms .= '<option value="'.$term->slug.'" '.$select.'>'. $term->name .' </option>';
//$i++;

// now the CHILDREN.
foreach($children as $child) {
$select = ($current_selected == $child->slug) ? "selected" : ""; // Note: child, not cterm
$list_of_terms .= '<option value="'.$child->slug.'" '.$select.'>'. $child->name.' </option>';

} //end foreach

if (count($children) > 0 ) {
$list_of_terms .= "</optgroup>";
}
}
}

$list_of_terms .= '</select>';

return $list_of_terms;
}

// FIRST DROPDOWN

add_action( 'wp_ajax_wpse158929_get_terms_for_cpt', 'wpse158929_get_terms_for_cpt' );
add_action( 'wp_ajax_nopriv_wpse158929_get_terms_for_cpt', 'wpse158929_get_terms_for_cpt' );

function wpse158929_get_terms_for_cpt() {
$ret = array( 'html' => '', 'error' => false );

if ( ! check_ajax_referer( 'wpse158929_get_terms_for_cpt_submit_', 'nonce', false /*die*/ ) ) {
$ret['error'] = __( 'Permission error', 'wpfm' );
} else {
$post_type = isset( $_REQUEST['post_type'] ) ? $_REQUEST['post_type'] : '';
$taxonomy = isset( $_REQUEST['taxonomy'] ) ? $_REQUEST['taxonomy'] : '';
$current_selected = isset( $_REQUEST['current_selected'] ) ? $_REQUEST['current_selected'] : '';

if ( ! $post_type || ! $taxonomy ) {
$ret['error'] = __( 'Params error', 'wpfm' );
} else {
global $wpdb;
$sql = $wpdb->prepare( 'SELECT t.slug FROM ' . $wpdb->terms . ' t'
. ' JOIN ' . $wpdb->term_taxonomy . ' AS tt ON tt.term_id = t.term_id'
. ' JOIN ' . $wpdb->term_relationships . ' AS tr ON tr.term_taxonomy_id = tt.term_taxonomy_id'
. ' JOIN ' . $wpdb->posts . ' AS p ON p.ID = tr.object_id'
. ' WHERE tt.taxonomy = %s AND p.post_type = %s AND p.post_status = %s'
. ' GROUP BY t.slug'
, $taxonomy, $post_type, 'publish' );
$include = $wpdb->get_col($sql);
$ret['html'] = preg_replace( '/<\/?select[^>]*>/', '', my_dropdown_categories( $taxonomy, $current_selected, $include ) );
}
}

wp_send_json( $ret );
}

А для страницы с выпадающими списками у меня есть:

                <form action="<?php bloginfo('url'); ?>" method="get">
<?php
//$post_type = get_post_type_object( get_post_type($post) ); // GET SINGULAR NAME
$args = array(
'public'   => true,
'_builtin' => false
);
$output = 'objects'; // names or objects, note names is the default
$operator = 'and'; // 'and' or 'or'
$post_types = get_post_types($args, $output, $operator);
ksort($post_types);
echo '<select data-placeholder="I need a:" class="fade-in three selectboxSingle" name="post_type">';
foreach ( $post_types as $post_type ) {
$exclude = array('competition');
if(TRUE === in_array($post_type->name,$exclude)){
continue;
}
// Note: I think you need to use query_var here, rather than slug.
echo '<option value="'.$post_type->query_var.'">' . ucfirst($post_type->labels->singular_name) . '</option>';
}
echo "</select>";
?>

<?php
// Set your custom taxonomy
$taxonomy = "location";
// Factored out taxonomy dropdown into function my_dropdown_categories() in "functions.php".
echo my_dropdown_categories( $taxonomy );
?>

<div class="submit-button-blanket">
<button class="submit-button alt" type="submit">Search</button>
</div>
</form>
</div>
</div>
</div>

<script type="text/javascript">
jQuery(document).ready(function($) {
var xhr;
var select_cpt, $select_cpt;
var select_location, $select_location;

$select_cpt = $(".selectboxSingle").selectize({
onChange: function(value) {
if (!value.length) return;
select_location.disable();
select_location.clearOptions();
select_location.load(function(callback) {
xhr && xhr.abort();
xhr = $.ajax({
url: "<?php echo admin_url('admin-ajax.php'); ?>",
success: function(results) {
select_location.enable();
callback(results);
},
error: function() {
callback();
}
})
});
}
});

$select_location = $('#location').selectize({
valueField: 'name',
labelField: 'name',
searchField: ['name']
});

select_location  = $select_location[0].selectize;
select_cpt = $select_cpt[0].selectize;

select_location.disable();
});

Сейчас я немного вышел из своей глубины, и любое руководство будет с благодарностью!