HistoryRenderCallback.php

<?php

namespace Drupal\history;

use Drupal\Core\Render\Element\RenderCallbackInterface;

/**
 * Render callback object.
 */
class HistoryRenderCallback implements RenderCallbackInterface {
    
    /**
     * #lazy_builder callback; attaches the last read timestamp for a node.
     *
     * @param int $node_id
     *   The node ID for which to attach the last read timestamp.
     *
     * @return array
     *   A renderable array containing the last read timestamp.
     */
    public static function lazyBuilder($node_id) {
        $element = [];
        $element['#attached']['drupalSettings']['history']['lastReadTimestamps'][$node_id] = (int) history_read($node_id);
        return $element;
    }

}