Prioritize native lazy-loading, load lazysizes like polyfill

(function () {

(function (Drupal, drupalSettings) {

  'use strict';

  function extend(obj, src) {

  Drupal.behaviors.lazy = {

    attach: function attach(context, settings) {

      var lazysizes = settings.lazy.lazysizes || {};

      if ('loading' in HTMLImageElement.prototype) {

        var images = document.querySelectorAll('img[loading="lazy"]');

        images.forEach(img => {

          img.src = img.getAttribute(lazysizes.srcAttr);

          this.removeClass(img, lazysizes.lazyClass);

          this.addClass(img, lazysizes.loadedClass);

        });

      }

      else {

        window.lazySizesConfig = window.lazySizesConfig || {};

        window.lazySizesConfig = this.extend(window.lazySizesConfig, lazysizes);

        var script = document.createElement('script'),

          scripts = document.getElementsByTagName('script')[0];

        script.src = Drupal.url('libraries/lazysizes/lazysizes.min.js');

        scripts.parentNode.insertBefore(script, scripts);

      }

    },

    extend: function extend(obj, src) {

      Object.keys(src).forEach(function (key) { obj[key] = src[key]; });

      return obj;

    },

    hasClass: function hasClass(el, className) {

      return el.classList ? el.classList.contains(className) : new RegExp('\\b'+ className+'\\b').test(el.className);

    },

    addClass: function addClass(el, className) {

      if (el.classList) el.classList.add(className);

      else if (!hasClass(el, className)) el.className += ' ' + className;

    },

    removeClass: function removeClass(el, className) {

      if (el.classList) el.classList.remove(className);

      else el.className = el.className.replace(new RegExp('\\b'+ className+'\\b', 'g'), '');

    }

  }

  var lazysizes = drupalSettings.lazy.lazysizes || {};

  window.lazySizesConfig = window.lazySizesConfig || {};

  window.lazySizesConfig = extend(window.lazySizesConfig, lazysizes);

})();

})(Drupal, drupalSettings);

  version: VERSION

  js:

    js/lazy.js: { }

  dependencies:

    - core/drupalSettings

lazysizes:

  header: true

  remote: https://github.com/aFarkas/lazysizes

  version: 5.1.1

  license:

    name: MIT

    url: https://github.com/aFarkas/lazysizes/blob/master/LICENSE

  js:

    /libraries/lazysizes/plugins/respimg/ls.respimg.min.js: { minified: true }

    /libraries/lazysizes/plugins/parent-fit/ls.parent-fit.min.js: { minified: true }

    /libraries/lazysizes/plugins/object-fit/ls.object-fit.min.js: { minified: true }

    /libraries/lazysizes/plugins/blur-up/ls.blur-up.min.js: { minified: true }

    /libraries/lazysizes/lazysizes.min.js: { minified: true }

  css:

    theme:

      css/lazysizes.css: { }

  dependencies:

    - lazy/lazy

    - core/drupal