storybook-1.x-dev/src/assets/js/attach-behaviors.js

/**
 * @file
 * Ensures that behaviors will attach, even in decoupled contexts, where
 * document.readyState is not a good indicator of DOM state.
 */

(function (Drupal, drupalSettings) {
  /**
   * Calls callback when document ready.
   *
   * @param {function} callback
   *   The function to be called on document ready.
   */
  const domReady = (callback) => {
    const listener = () => {
      callback();
      document.removeEventListener('DOMContentLoaded', listener);
    };
    document.addEventListener('DOMContentLoaded', listener);
  };

  // Attach all behaviors.
  domReady(() => {
    Drupal.attachBehaviors(document, drupalSettings);
  });
})(Drupal, window.drupalSettings);