Service Worker

sw.js

/*
 *  EVE Milano sw.js
 *  Copyright 2017 Giovanni Sacheli All rights reserved.
 *  Version 1.2 (20 settembre 2017)
 */

self.addEventListener('install', e => {
	console.log('PWA Service Worker installing.');
    let timeStamp = Date.now();
    e.waitUntil(
    caches.open('evemilano_service_worker').then(cache => {
      return cache.addAll([
		'/wp-content/themes/metro-pro/style.css',
                '/',
		'/?utm_source=homescreen',
		'/wp-content/uploads/2015/07/logo-blu-270x80-da-vettoriale.png',
		'/wp-content/plugins/eve_social_buttons/images/socicon.eot',
		'/wp-content/plugins/eve_social_buttons/images/socicon.woff',
		'/wp-content/plugins/eve_social_buttons/images/socicon.ttf',
		'/wp-content/plugins/eve_social_buttons/images/socicon.svg'
      ])
      .then(() => self.skipWaiting());
    })
  )
});

self.addEventListener('activate',  event => {
  console.log('PWA Service Worker activating.');  
  event.waitUntil(self.clients.claim());
});

self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request).then(response => {
      return response || fetch(event.request);
    })
	
  );
});

Guida: https://www.evemilano.com/2017/10/progressive-web-app/