WordPress: Examples of menu filters (including nav menu widgets)

menu-filters.php

<?php

/**
 * Menu: Filters
 */


/**
 * WP_Nav_Menu_Widget: Edit params to add wrapping HTML
 */
function dt_filter_dynamic_sidebar_params($params)
{

    if ($params[0]['widget_name'] == "Navigation Menu") {
        $params[0]['before_widget'] = '<div class="section__aside-inner">';
        $params[0]['after_widget'] = '</div><!-- /.section__aside-inner -->';
        $params[0]['before_title'] = '<h3>';
        $params[0]['after_title'] = '</h3>';
    }

    return $params;
}
// add_filter( 'dynamic_sidebar_params', 'dt_filter_dynamic_sidebar_params' ); 


/**
 * WP_Nav_Menu_Widget: Edit wp_nav_menu args
 *
 * Among other things, this filter is used to add an identifying class to container
 * for use in other menu filters
 */
function dt_filter_widget_nav_menu_args($nav_menu_args, $nav_menu, $args, $instance)
{

    if ($args['widget_name'] == 'Navigation Menu') {

        $nav_menu_args['container_class'] = 'section__aside-menu dt-filter-tag__nav-menu-widget'; // dt-filter-tag needed for other filters

        $nav_menu_args['walker'] = new Walker_Nav_Menu(); // needed to access has_children property in menu filters

        $nav_menu_args['container'] = 'nav';
    }

    return $nav_menu_args;
};
// add_filter( 'widget_nav_menu_args', 'dt_filter_widget_nav_menu_args', 10, 4 ); 


/**
 * Nav menus: Add classes to <li> elements
 */
function dt_filter_nav_menu_css_class($array, $item, $args, $depth)
{

    /**
     * WP_Nav_Menu_Widget: this filter works in conjuction with the
     * widget_nav_menu_args filter using the identifying container class 
     * dt-filter-tag__nav-menu-widget
     */
    if (
        $args->container_class
        && (strpos($args->container_class, 'dt-filter-tag__nav-menu-widget') !== false)
        && ($depth == 0)
    ) {

        if ($args->walker->has_children === true) {
            $array[] = 'has-submenu js-equal-heights-parent';
        }
    }

    return $array;
};
// add_filter( 'nav_menu_css_class', 'dt_filter_nav_menu_css_class', 10, 4 ); 


/**
 * Nav menus: Add classes to <a> elements
 */
function dt_filter_nav_menu_link_attributes($atts, $item, $args, $depth)
{

    /**
     * WP_Nav_Menu_Widget: Add class to links
     * 
     * This filter works in conjuction with the
     * widget_nav_menu_args filter using the identifying container class 
     * dt-filter-tag__nav-menu-widget
     */
    if ($args->container_class && strpos($args->container_class, 'dt-filter-tag__nav-menu-widget') !== false) {

        if ($depth == 0) {
            $atts['class'] = 'js-equal-height';
        }
    }

    $contact_page_id = 13; // TODO Update if used

    // Main menu: Add extra classes to top level links
    if (('primary' == $args->theme_location) &&
        (0 == $depth)
    ) {

        $atts['class'] = 'btn btn--transparent';

        // Add class to Contact menu item
        if ($contact_page_id  == $item->object_id) {
            $atts['class'] .= ' btn--bordered';
        }
    }

    // Secondary footer menu: Add extra classes to Contact menu item
    if (('footer-secondary' == $args->theme_location) &&
        ($contact_page_id == $item->object_id)
    ) {

        $atts['class'] = 'btn btn--transparent btn--bordered';
    }

    return $atts;
};
// add_filter( 'nav_menu_link_attributes', 'dt_filter_nav_menu_link_attributes', 10, 4 );


/**
 * Nav menus: Add class to submenu <ul> elements
 */
function dt_filter_nav_menu_submenu_css_class($classes, $args, $depth)
{

    /**
     * WP_Nav_Menu_Widget: this filter works in conjuction with the
     * widget_nav_menu_args filter using the identifying container class 
     * dt-filter-tag__nav-menu-widget
     */
    if ($args->container_class && strpos($args->container_class, 'dt-filter-tag__nav-menu-widget') !== false) {
        $classes = ['sub-menu-alt'];
    }

    // Change submenu class in primary menu location
    if ('primary' == $args->theme_location) {
        $classes = ['dropdown'];
    }

    return $classes;
}
// add_filter( 'nav_menu_submenu_css_class', 'dt_filter_nav_menu_submenu_css_class', 10, 3 );


/**
 * Nav menu: Edit wp_nav_menu html
 */
function dt_filter_nav_menu_widget_edit_html($array, $int)
{

    /**
     * WP_Nav_Menu_Widget: this filter works in conjuction with the
     * widget_nav_menu_args filter using the identifying container class 
     * dt-filter-tag__nav-menu-widget
     */
    if ($args->container_class && strpos($args->container_class, 'dt-filter-tag__nav-menu-widget') !== false) {

        // Replace containers start
        $array = str_replace('<nav class="dt-nav-menu-widget">', '<div class="widget__body"><nav class="nav-vertical">', $array);

        // Replace containers end
        $array = str_replace('</nav>">', '</nav><!-- /.nav-vertical --></div><!-- /.widget__body -->', $array);

        // Add 'current' class
        $array = str_replace('current', 'current current', $array);
    }

    return $array;
};
// add_filter( 'wp_nav_menu', 'dt_filter_nav_menu_widget_edit_html', 10, 2 ); 



/**
 * Nav menu: Edit args for a nav menu item
 */
function dt_filter_nav_menu_item_args($args, $item, $depth)
{

    // Add spans before <a> tags on top level menu items in primary menu location
    if ('primary' == $args->theme_location) {

        if (0 == $depth) {
            $args->before = '<span class="trigger-dropdown"></span>';
        } else {
            $args->before = '';
        }
    }

    return $args;
}
// add_filter( 'nav_menu_item_args', 'dt_filter_nav_menu_item_args', 10, 3 );