<?php
function custom_wp_nav_menu($var) {
	return is_array($var) ? array_intersect($var, array(
		//List of allowed menu classes
		'current_page_item',
		'current_page_parent',
		'current_page_ancestor',
		'first',
		'last',
		'vertical',
		'horizontal'
		)
	) : '';
}
add_filter('nav_menu_css_class', 'custom_wp_nav_menu');
add_filter('nav_menu_item_id', 'custom_wp_nav_menu');
add_filter('page_css_class', 'custom_wp_nav_menu');

//Replaces "current-menu-item" with "active"
function current_to_active($text){
	$replace = array(
		//List of menu item classes that should be changed to "active"
		'current-menu-item' => 'active',
		'current_page_parent' => 'active',
		'current_page_ancestor' => 'active',
	);
	$text = str_replace(array_keys($replace), $replace, $text);
		return $text;
	}
add_filter('nav_menu_css_class', 'current_to_active');
add_filter('nav_menu_item_id', 'current_to_active');
add_filter('page_css_class', 'current_to_active');

//Deletes empty classes and removes the sub menu class
function strip_empty_classes($menu) {
    $menu = preg_replace('/ class=""| class="sub-menu"/','',$menu);
    return $menu;
}
add_filter ('wp_nav_menu','strip_empty_classes');
?>