Basic jQuery independent ES6 JS for Drupal 9.2+ project (module, theme)

myproject.es6.js

/**
 * @file
 * Behaviors for My Project.
 */

((Drupal, settings, once) => {
  /**
   * Holds functions, methods, settings and other information for My Project.
   *
   * @namespace
   */
  Drupal.myproject = {
    preInit(context) {},
    init(settings) {},
    postInit() {},
  };

  /**
   * Attaches the My Project behaviors for STUFFS.
   *
   * @type {Drupal~behavior}
   *
   * @prop {Drupal~behaviorAttach} attach
   *   Call pre-init function when the DOM is ready.
   *   Call init function when DOM content is loaded but before images load.
   *   Call post-init function when the page has loaded.
   */
  Drupal.behaviors.myproject = {
    attach(context, settings) {
      Drupal.myproject.preInit(context);
      window.addEventListener('DOMContentLoaded', () => {
        once('myprojectInit', 'html', context).forEach(() => {
          Drupal.myproject.init(settings);
          window.addEventListener('load', () => {
            Drupal.myproject.postInit();
          });
        });
      });
    },
  };
})(Drupal, drupalSettings, once);

myproject.libraries.yml

global-scripts:
  js: 
    js/myproject.js: {}
  dependencies:
    - core/drupal
    - core/drupalSettings
    - core/once