drupal/core/modules/history/js/mark-as-read.es6.js

/**
 * @file
 * Marks the nodes listed in drupalSettings.history.nodesToMarkAsRead as read.
 *
 * Uses the History module JavaScript API.
 *
 * @see Drupal.history
 */

(function (window, Drupal, drupalSettings) {
  // When the window's "load" event is triggered, mark all enumerated nodes as
  // read. This still allows for Drupal behaviors (which are triggered on the
  // "DOMContentReady" event) to add "new" and "updated" indicators.
  window.addEventListener('load', () => {
    if (drupalSettings.history && drupalSettings.history.nodesToMarkAsRead) {
      Object.keys(drupalSettings.history.nodesToMarkAsRead).forEach(Drupal.history.markAsRead);
    }
  });
}(window, Drupal, drupalSettings));