If you Read Then Code Then you see How add Class in WordPress Menu With add Class jQuery

Wp Menu Add Class li. Menu add class li a.

<?php

//Menu li add class
-----------------

function add_menuclass($ulclass) {
   return preg_replace('/<li /', '<li class="scroll"', $ulclass);
}
add_filter('wp_nav_menu','add_menuclass');


//Menu li a add class
--------------------
function add_menuclass($ulclass) {
   return preg_replace('/<a /', '<a class="nav-link"', $ulclass);
}
add_filter('wp_nav_menu','add_menuclass');


//How to Add the First and Last Class to WordPress Navigation Menu Items
------------------------------------------------------------------------
function wpb_first_and_last_menu_class($items) {
    $items[1]->classes[] = 'first';
    $items[count($items)]->classes[] = 'last';
    return $items;
}
add_filter('wp_nav_menu_objects', 'wpb_first_and_last_menu_class');


//Current Menu Item
function special_nav_class ($classes, $item) {
    if (in_array('current-menu-item', $classes) ){
        $classes[] = 'active ';
    }
    return $classes;
}
add_filter('nav_menu_css_class' , 'special_nav_class' , 10 , 2);


//Single Menu Add class
----------------------
function service_menu_class( $classes, $item, $args ) {
    if ( 'servicenav' === $args->theme_location ) {
    $classes[] = 'col-md-4';
}
    return $classes;
}
add_filter( 'nav_menu_css_class', 'service_menu_class', 10, 3 );



//Add Menu My Cart last menu
----------------------------
function search_icon_add_in_mainmenu($items, $args){
    if( $args->theme_location == 'primary_menu') {

        $items .= '
        <li><a href="'.home_url().'/wishlist"><i class="fa fa-heart-o"></i>Wishlist</a></li>
        <li><a href="'.wc_get_cart_url().'"><i class="fa fa-shopping-cart"></i>My Cart <span>'.sprintf ( _n( '%d', '%d', WC()->cart->get_cart_contents_count() ), WC()->cart->get_cart_contents_count() ).'</span></a></li>';
    }
    return $items;
}
add_filter( 'wp_nav_menu_items', 'search_icon_add_in_mainmenu', 200, 2 );

//Remove wrapping div and ul from output of wp_nav_menu
----------------------------
'container'      => '',
'items_wrap'     => '%3$s',




$(function() {

    "use strict";

    //WP MENU ADD CLASS FRIST ITEM:
    -----------------------------
     $("#menu-header-menu li a").first().addClass( "active" );
    
      //last  2 child add class
      ------------------------
      $('ul.menu>li').slice(-2).addClass('last-elements');

    How to add class to first child with jQuery?

    $('ul li').each(function(i) {
        if ( i === 2 ) {
           $(this).addClass('aaaa');
        }
    });

})(window.jQuery);