parent menu item class

<?php


// Widget Settings

if ( function_exists('register_sidebar') )
	register_sidebar(array(
		'name' => 'Left Navigation',
		'before_widget' => '<div class="left-widget">',
	'after_widget' => '</div>',
	'before_title' => '<div class="widget-header">',
	'after_title' => '</div>',
	));

if ( function_exists('register_sidebar') )
	register_sidebar(array(
		'name' => 'Right Navigation',
		'before_widget' => '<div class="right-widget">',
	'after_widget' => '</div>',
	'before_title' => '<div class="widget-header">',
	'after_title' => '</div>',
	));


// add parent menu item class

add_filter('wp_nav_menu_objects', function ($items) {
    $hasSub = function ($menu_item_id, &$items) {
        foreach ($items as $item) {
            if ($item->menu_item_parent && $item->menu_item_parent==$menu_item_id) {
                return true;
            }
        }
        return false;
    };

    foreach ($items as &$item) {
        if ($hasSub($item->ID, &$items)) {
            $item->classes[] = 'menu-parent-item'; // all elements of field "classes" of a menu item get join together and render to class attribute of <li> element in HTML
        }
    }
    return $items;
});

?>