Wordpress Menu BEM-style classes

functions.php

<?php

/**
 * Adds classes for menu link
 * If menu container has classes [base-menu baseMenu]
 * than links will get classes [base-menu--link baseMenuLink]
 */
add_filter('nav_menu_link_attributes', function ($atts, $item, $args, $depth)
{
    $classes = explode(' ', $args->container_class ?: $args->menu_class);

    $classes = array_map(function ($class_name_base)
    {
        $link_class_name = trim($class_name_base);

        if (mb_strpos($link_class_name, '__') !== FALSE) // base class name with Modifier
        {
            return FALSE;
        }

        if (is_camelcase_string($link_class_name))
        {
            $link_class_name .= 'Link'; // JS class name
        }
        elseif ($link_class_name) // simple BEM class name
        {
            $link_class_name .= '--link';
        }

        return $link_class_name;
    }, $classes);

    $classes = array_filter($classes);

    $atts['class'] = implode($classes, ' ');

    return $atts;
}, 10, 4);

/**
 * Adds classes for menu items
 * If menu container has classes [base-menu baseMenu]
 * than items will get classes [base-menu--item baseMenuItem]
 * Additionally items will get classes [base-menu--item__current base-menu--item__has-children]
 * if it will possible
 */
add_filter('nav_menu_css_class', function ($classes, $item, $args)
{
    $classes_origin = $classes;

    $classes_base = explode(' ', $args->container_class ?: $args->menu_class);

    $classes = array_map(function ($class_name_base) use ($classes_origin)
    {
        $item_class_name = trim($class_name_base);

        if (mb_strpos($item_class_name, '__') !== FALSE) // base class name with Modifier
        {
            return FALSE;
        }

        if (is_camelcase_string($item_class_name))
        {
            $item_class_name .= 'Item'; // JS class name
        }
        elseif ($item_class_name) // simple BEM class name
        {
            $item_class_name .= '--item';

            $item_classes = [$item_class_name];

            if (in_array('current-menu-item', $classes_origin) OR in_array('current-menu-parent', $classes_origin))
            {
                $item_classes[] = $item_class_name . '__current';
            }

            if (in_array('menu-item-has-children', $classes_origin))
            {
                $item_classes[] = $item_class_name . '__has-children';
            }

            $item_class_name = implode($item_classes, ' ');
        }

        return $item_class_name;
    }, $classes_base);

    $classes = array_filter($classes);

    return $classes;
}, 10, 3);

function is_camelcase_string($subject)
{
    return preg_match('~[A-Z][a-z]~u', $subject);
}