remove li class & id for menu items and pages list

Question

Example of WordPress default CSS class output:

&l         


        

Answer 1

If you just want to remove all the list classes and id's, add this to functions.php

add_filter('nav_menu_item_id', 'filter_menu_id');
add_filter( 'nav_menu_css_class', 'filter_menu_li' );
function filter_menu_li(){
    return array('');   
}
function filter_menu_id(){
    return; 
}

Answer 2

An addition to Richard's answer: We need to clean up the empty classes left behind:

//Strip Empty Classes
add_filter ('wp_nav_menu','strip_empty_classes');
function strip_empty_classes($menu) {
    $menu = preg_replace('/ class=(["\'])(?!active).*?\1/','',$menu);
    return $menu;
}