Add custom meta to nav menu items

here is a quick code that should do the job, paste this in your theme’s functions.php file

basically what it does is hide all regular class input boxes and adds a new select dropdown which changes the value of the hidden input based on the selected value.

and it looks like this;

function menu_item_class_select(){
    global $pagenow;
    if ($pagenow == "nav-menus.php"){
    ?>
    <script>
    jQuery(document).ready(function(){
        function create_dd(v){
            //create dropdown
            var dd = jQuery('<select class="my_class"></select>');
            //create dropdown options
            //array with the options you want
            var classes = ["","class1","class2","class3"];
            jQuery.each(classes, function(i,val) {
                if (v == val){
                    dd.append('<option value="'+val+'" selected="selected">'+val+'</option>');
                }else{
                    dd.append('<option value="'+val+'">'+val+'</option>');
                }
            });
            return dd;
        }

        jQuery(".edit-menu-item-classes").each(function() {
            //add dropdown
            var t = create_dd(jQuery(this).val());
            jQuery(this).before(t);
            //hide all inputs
            jQuery(this).css("display","none");

        });
        //update input on selection
        jQuery(".my_class").bind("change", function() {
            var v = jQuery(this).val();
            var inp = jQuery(this).next();
            inp.attr("value",v);
        });
    });


    </script>
    <?php
    }
}
add_action('admin_footer','menu_item_class_select');