CODE EXAMPLE FOR PHP

wordpress add class on navigation menu

// add a custom class to nav_menu li
function add_additional_class_on_li($classes, $item, $args) {

    if (isset($args->add_li_class)) {
        $classes[] = $args->add_li_class;
    }
    return $classes;
}
add_filter('nav_menu_css_class', 'add_additional_class_on_li', 1, 3);

// add a custom class to nav_menu anchor
function add_additional_class_on_anchor($classes, $item, $args) {

    if (isset($args->add_anchor_class)) {
        $classes['class'] = $args->add_anchor_class;
    }

    return $classes;
}
add_filter('nav_menu_link_attributes', 'add_additional_class_on_anchor', 1, 3);

// code on header
@php
$nav_classes = [
'theme_location' => 'primary_navigation',
// div tag
'container_class' => 'ml-auto',
// ul tag
'menu_class' => 'nav justify-content-center',
//li tag
'add_li_class' => 'nav-item',
//a tag
'add_anchor_class' => 'nav-link',
];

if (has_nav_menu('primary_navigation')) {
  //display navigation menu
echo wp_nav_menu($nav_classes);
}
@endphp