polyfill.js

'use strict';
// Polyfills for (old) mobile browsers and IE 11
// From https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/
if (!String.prototype.includes) {
  String.prototype.includes = function () {
    return String.prototype.indexOf.apply(this, arguments) !== -1;
  };
}

if (typeof Object.assign !== 'function') {
  Object.assign = function (target, varArgs) { // .length of function is 2
    if (target == null) { // TypeError if undefined or null
      throw new TypeError('Cannot convert undefined or null to object');
    }

    var to = Object(target);

    for (var index = 1; index < arguments.length; index++) {
      var nextSource = arguments[index];

      if (nextSource != null) { // Skip over if undefined or null
        for (var nextKey in nextSource) {
          // Avoid bugs when hasOwnProperty is shadowed
          if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
            to[nextKey] = nextSource[nextKey];
          }
        }
      }
    }
    return to;
  };
}

// eslint-disable-next-line consistent-return
(function () {
  if (typeof window.CustomEvent === 'function') {
    return false;
  }

  function CustomEvent(event, params) {
    params = params || { bubbles: false, cancelable: false, detail: undefined };
    var evt = document.createEvent('CustomEvent');
    evt.initCustomEvent(event, params.bubbles, params.cancelable, params.detail);
    return evt;
  }

  CustomEvent.prototype = window.Event.prototype;

  window.CustomEvent = CustomEvent;
})();

if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('service-worker.js');
}