How to Modify Default “Sub-Menu” Class for Child Menu in WordPress

Sometimes we are needed to modify the default “sub-menu” class for the child menu in WordPress. There is no direct way you can do that but this can be done by placing a sample code in your functions.php like below:

function cdxn_change_submenu_class($menu) {  
    $menu = preg_replace('/class="sub-menu"/', '/class="newclass"/', $menu);  
    return $menu;  
}  
add_filter('wp_nav_menu','cdxn_change_submenu_class');