Here is how to add a Data Attribute to a Menu List Item via the Walker Menu Class. Some of the markup of  the WordPress menu is hard to filter or hook into, the Walker class allows for a full custom menu mark up.

One request I find is to add a data attribute to the list item itself, instead of the link tag <a> which can be accomplished using nav_menu_link_attributes , for the <li> item you will need to create a whole new menu using the Walker Menu Class.

Register and Position a New Menu

First up is to register a new menu and link it to an instance of the Walker Class

View the code on Gist.

So in the above gist I am registering a new menu with wp_nav_menu with a theme location of tertiary, adding support for it with add_theme_support  as I am using Genesis and also positioning it before the loop with an action.

Notice in the $args for wp_nav_menu I am giving a value to ‘walker’ – this is the new instance of the walker class named WPB_Custom _Walker

Making a New Walker Class Instance

Make a copy of class Walker_Nav_Menu from  the original /wp-includes/class-walker-nav-menu.php – here I have added it to my theme’s /inc directory and named it custom-walker.php Make sure you change the class name from the original in the file, my one starts – class WPB_Custom_Walker extends Walker

View the code on Gist.

In essence now the new menu will follow the new walker instance so you can alter the output in custom-walker.php which will reflect on the rendered output on the new menu.

Adding Custom Fields for Data Attributes

There is a great library that allows us to add custom fields to the menu items in the backend of WordPress, which we then can output in our custom-walker.php file.

The library is here. Download it and extract the files in the screen grab, remember we already have custom-walker.php  and add into your themes /inc folder and bring in one of them to your functions.php file.

custom-walker-class

Bring in menu-item-custom-fields.php into functions.php

require_once dirname( __FILE__ ) . '/inc/menu-item-custom-fields.php';

This file menu-item-custom-fields.php in turn references the other walker-nav-menu-edit.php and the file in the doc directory – walker-nav-menu-edit.php gives us our sample custom fields which need to be copied and added to functions.php

View the code on Gist.

So in the above I have added one new specific field and left the other one at the default text…

self::$fields = array(
 'field_description' => __( 'Data Content', 'menu-item-custom-fields-example' ),
 'field_02' => __( 'Custom Field #2', 'menu-item-custom-fields-example' ),
 );

I have also changed any text from menu-item-%s to  _menu_item_%s in the function _save and function_fields

This is then ready in the admin backend…

custom-fields-in-menu

 

Output in the Front End Markup

Final thing is to retrieve the field with get_post_meta in the custom-walker.php file

 $item->datacontent = get_post_meta( $item->ID, '_menu_item_field_description', true );

Then call it in the <li> item

 $output .= $indent . '<li' . $attributes . $id . $class_names . 'data-content="' . $item->datacontent . '">';

custom-walker.php with custom field added at line 81 and called in the output at line 123

View the code on Gist.

data-attribute-list-item-wordpress

 

Mammoth task complete! – In some instances you may just want to add a jQuery fix but in others you may need the attribute value to change by the end user in which case you’ll need a custom solution.

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