Quick and dirty WordPress drop-in plugin to generate BreadcrumbList structured data for nested posts/pages

parkwood-json-ld-breadcrumbs.php

<?php
/*
Plugin Name: Parkwood JSON-LD Breadcrumbs
Plugin URI: http://www.parkwooddigital.com/
Description: Generate JSON-LD breadcrumbs structured data for Google on pages
Author: Jon Parker <[email protected]>
Version: 1.0
Author URI: http://www.parkwooddigital.com/
*/

function parkwood_json_ld_breadcrumbs() {
  global $post;
  $ancestors = get_post_ancestors( $post->ID );

  if ( $ancestors ) {
    $ancestors = array_reverse($ancestors);
    $ancestors[] = $post->ID;
  }

  if ( $ancestors ) {
  ?>
  <script type="application/ld+json">
  {
    "@context": "http://schema.org",
    "@type": "BreadcrumbList",
    "itemListElement":
    [
      <?php foreach($ancestors as $key => $id): ?>
        {
          "@type": "ListItem",
          "position": <?php echo $key + 1; ?>,
          "item":
          {
            "@id": "<?php echo get_permalink($id); ?>",
            "name": "<?php echo esc_js( get_the_title($id) ); ?>"
          }
        }<?php echo ( $key + 1 < count($ancestors) ) ? ',' : '' ; ?>
      <?php endforeach; ?>
    ]
  }
  </script>
  <?php
  } // end if
}

add_action( 'wp_head', 'parkwood_json_ld_breadcrumbs' );