WordPress: Add the page or post slug as a class to a menu item.

wp-slug-class-to-menu.php

<?php

/**
 * Add the page or post slug as a class to a menu item.
 * Add to functions.php
 */
function add_slug_class_to_menu_item($output){
	$ps = get_option('permalink_structure');if(!empty($ps)){
		$idstr = preg_match_all('/<li id="menu-item-(\d+)/', $output, $matches);
		foreach($matches[1] as $mid){
			$id = get_post_meta($mid, '_menu_item_object_id', true);
			$slug = basename(get_permalink($id));
			$output = preg_replace('/menu-item-'.$mid.'">/', 'menu-item-'.$mid.' menu-item-'.$slug.'">', $output, 1);
		}
	}
	return $output;
}
add_filter('wp_nav_menu', 'add_slug_class_to_menu_item');