Question

Example of WordPress default CSS class output:

<li id="menu-item-55" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-55">

<li class="page_item page-item-37">

The menu and pages list item come with various own li class and id.

How to remove them in functions.php file for the menu and for the pages list?

Answer 1

You should be able to remove them by hooking into a couple of filters and returning empty arrays or strings rather than new classes or ids:

add_filter('nav_menu_css_class', 'my_css_attributes_filter', 100, 1);
add_filter('nav_menu_item_id', 'my_css_attributes_filter', 100, 1);
add_filter('page_css_class', 'my_css_attributes_filter', 100, 1);
function my_css_attributes_filter($var) {
  return is_array($var) ? array() : '';
}

---

If you wanted to keep particular classes you could do something like this:

function my_css_attributes_filter($var) {
  return is_array($var) ? array_intersect($var, array('current-menu-item')) : '';
}