How to use nav_menu_css_class filter in WordPress

nav_menu_css_class filter

Filters the CSS classes applied to a menu item’s list item element.

To use the nav_menu_css_class filter, first you have to register it using add_filter. You can write this code into functions.php of your activated theme or in a custom WordPress Plugin. At WePlugins, we always prefer to create a custom WordPress Plugin while using hooks so nothing breaks when you update your WordPress Theme in the future.

In the below live example, we have defined a function modify_nav_menu_css_class_defaults which takes 4 parameters and we registered using add_filter. The first parameter nav_menu_css_class is the name of the hook, the second parameter modify_nav_menu_css_class_defaults is the name of the function which needs to be called, the third parameter is the priority of calling the hook if the same hook is used multiple times, and the last parameter is the number of arguments (if any) to be passed in the registered function.

Sometimes, you have to remove a registered hook so you can use remove_filter to remove the nav_menu_css_class filter.

Parameters

Below are the 4 parameters required to use this hook.

• $classes : (string[]) Array of the CSS classes that are applied to the menu item’s <li> element.
• $menu_item : (WP_Post) The current menu item object.
• $args : (stdClass) An object of wp_nav_menu() arguments.
• $depth : (int) Depth of menu item. Used for padding.

Live Example

Basic Filtering

Below is an example of how you can use this hook to filter menu item classes.

        function weplugins_modify_nav_menu_css_class_defaults($classes, $menu_item, $args, $depth) { 
            // Update the $classes variable according to your website requirements and return this variable. You can modify the $classes variable conditionally too if you want.
            return $classes; 
        }
        // Add the filter
        add_filter("nav_menu_css_class", "weplugins_modify_nav_menu_css_class_defaults", 10, 4);
    

Removing a Hook

To remove a hook callback, use the example below.

        remove_filter("nav_menu_css_class", "weplugins_modify_nav_menu_css_class_defaults", 10, 4);
    

Please make sure to provide the same callback function name, priority, and number of arguments while removing the hook callback.

Advanced Example

Here’s a more advanced example where you conditionally modify the CSS classes based on the menu item.

        function weplugins_modify_nav_menu_css_class_advanced($classes, $menu_item, $args, $depth) {
            if ($menu_item->ID == '42') {
                $classes[] = 'custom-class';
            }
            return $classes;
        }
        add_filter("nav_menu_css_class", "weplugins_modify_nav_menu_css_class_advanced", 10, 4);