Sage main javascript file with google maps from https://www.npmjs.com/package/google-maps

main.js

// import external dependencies
import 'jquery';
import 'bootstrap/dist/js/bootstrap';
import GoogleMapsLoader from 'google-maps';

// import local dependencies
import Router from './util/router';
import common from './routes/Common';
import home from './routes/Home';
import aboutUs from './routes/About';

// Use this variable to set up the common and page specific functions. If you
// rename this variable, you will also need to rename the namespace below.
const doLoadGmap = (el, options) => {
  const newMap = new window.google.maps.Map(el, options);
  return newMap;
};

const mapEl = document.getElementById('map');
const mapOpts = {
  center: { lat: -34.397, lng: 150.644 },
  scrollwheel: false,
  zoom: 8,
};
GoogleMapsLoader.KEY = 'AIzaSyAdQZEV2sGV_6ILHJ0xBToBnmVKGtLo19U';
GoogleMapsLoader.load(doLoadGmap(mapEl, mapOpts));

const routes = {
  // All pages
  common,
  // Home page
  home,
  // About us page, note the change from about-us to aboutUs.
  aboutUs,
};

// Load Events
document.addEventListener('DOMContentLoaded', () => new Router(routes).loadEvents());