How to add a data attribute to a WordPress menu item

Question

I'm Twitter Bootstrap and need to add data-toggle="modal" attribute to the a tag of menu link. Upon searching most all results reference doing a walking for Twitter Bootstrap dropdown menus however this menu has no dropdowns and I only need to add the particular attribute.

Next I found this: Add custom attributes to menu items without plugin which is very helpful as it appears in WordPress 3.6+ we no longer have to do long complex walkers and instead can use this: http://codex.wordpress.org/Plugin_API/Filter_Reference/nav_menu_link_attributes

However as of this running that API reference is quite bare and offers no examples and since it's so new there are very few references to it on Google.

I tried this first:

add_filter( 'nav_menu_link_attributes', 'mywp_contact_menu_atts', 10, 3 );

function pb_contact_menu_atts( $atts, $item, $args )
{
    // inspect $item, then …
    $atts['data-toggle'] = 'modal';
    return $atts;
}

and that does work however it as expected adds the attribute to all the a tags in the menu. So I'm trying to figure out how to target one menu item with #menu-item-7857 a or such.

Does anyone know where to find an example of targeting a menu item or able to determine how to basd on the information that's in the above linked API reference?

To note, I did find the following one example but it only targets items that have children which does not help but may be in the right direction:

add_filter('nav_menu_link_attributes', function($atts, $item, $args) {
    if ( $args->has_children )
    {
        $atts['data-toggle'] = 'dropdown';
        $atts['class'] = 'dropdown-toggle';
    }

    return $atts;
}, 10, 3);

UPDATE - The only answer below sounds like it's on to something but from it wasn't able to determine how to actually find the number to target my specific link and where/how to add that conditional in a working example. Added a comment but didn't hear back. Since been about 18 days thought I'd see if a bounty would help.

When I look at the code for the link I want to target:

<li id="menu-item-7858" class="menu-item menu-item-type-custom menu-item-object-custom menu-item-7858"><a href="#" data-toggle="modal">Chat</a></li>

I see the number 7858 so thinking maybe that is the number I should be targeting.

But when I try for instance:

add_filter( 'nav_menu_link_attributes', 'my_chat_menu_atts', 10, 3 );


function my_chat_menu_atts( $atts, $item, $args ) {
    if ( 7857 == $item['ID'] ) {
        // inspect $item, then …
        $atts['onclick'] = 'SnapEngage.startLink();';
        return $atts;
    }
}

However adding that if statement the one commenter suggested I get the following error:

Fatal error: Cannot use object of type WP_Post as array

I'm assuming more code is required but at a lost. As a reminder without the if statement it works however it targets all links rather than the one link I want to target.

Answer 1

Specifically editing the code you provided in the original question:

add_filter( 'nav_menu_link_attributes', 'wpse121123_contact_menu_atts', 10, 3 );
function wpse121123_contact_menu_atts( $atts, $item, $args )
{
  // The ID of the target menu item
  $menu_target = 123;

  // inspect $item
  if ($item->ID == $menu_target) {
    $atts['data-toggle'] = 'modal';
  }
  return $atts;
}

Answer 2

The second $item argument, which is being made available to your filter function, contains a menu item object. If dumped it looks something like this:

[1] => WP_Post Object
    (
        [ID] => 2220
        [post_author] => 1
        [post_date] => 2012-12-26 19:29:44
        [post_date_gmt] => 2012-12-26 17:29:44
        [post_content] => 
        [post_title] => Home
        [post_excerpt] => 
        [post_status] => publish
        [comment_status] => open
        [ping_status] => open
        [post_password] => 
        [post_name] => home-3
        [to_ping] => 
        [pinged] => 
        [post_modified] => 2013-06-05 01:55:20
        [post_modified_gmt] => 2013-06-04 22:55:20
        [post_content_filtered] => 
        [post_parent] => 0
        [guid] => http://dev.rarst.net/?p=2220
        [menu_order] => 1
        [post_type] => nav_menu_item
        [post_mime_type] => 
        [comment_count] => 0
        [filter] => raw
        [db_id] => 2220
        [menu_item_parent] => 0
        [object_id] => 2220
        [object] => custom
        [type] => custom
        [type_label] => Custom
        [title] => Home
        [url] => http://dev.rarst.net/
        [target] => 
        [attr_title] => 
        [description] => 
        [classes] => Array
            (
                [0] => 
                [1] => menu-item
                [2] => menu-item-type-custom
                [3] => menu-item-object-custom
                [4] => current-menu-item
                [5] => current_page_item
                [6] => menu-item-home
            )

        [xfn] => 
        [current] => 1
        [current_item_ancestor] => 
        [current_item_parent] => 
    )

To target specific menu item you need to formulate your condition and check it against data available in the object, for example if ( 2220 == $item['ID'] )

Answer 3

Why don't you approach this problem from a different direction? Rather than attempting to target the menu item with id == ?? which could change at some point (the menu item, not the id), use the WP Admin area to add a custom class to the menu item you want to target. Then use that class in your Javascript to trigger the information you need:

$('.my-class').click(function(e){
  // do other stuff
  e.preventDefault;
});

My javascript is not guaranteed. If you're not using jQuery, you could try this.

Answer 4

I wanted to add data-letters to the custom menu that I had created in WordPress.

The steps I chose was:

1. Found my menu's id number.
2. added those lines of code from @guiniveretoo
3. wrote if statements for each menu items (as I wanted different attribute values to be injected.)
4. worked!

Here is my code.

add_filter( 'nav_menu_link_attributes', 'wpse121123_contact_menu_atts', 10, 3 );
function wpse121123_contact_menu_atts( $atts, $item, $args )
{  
  $menu_target = 6;

  if ($item->ID == $menu_target) {
    $atts['data-letters'] = 'PROJECTS';
  }

  elseif ($item->ID == 7) {
    $atts['data-letters'] = 'RESUME';
  }
  elseif ($item->ID == 8) {
    $atts['data-letters'] = 'ARTWORKS';
  }
  elseif ($item->ID == 9) {
    $atts['data-letters'] = 'HELLO!';
  }
  return $atts;
}

Hope this helps you.