sw.js

// This is the service worker with the combined offline experience (Offline page + Offline copy of pages)

const CACHE = "pwabuilder-offline-page";

// importScripts('https://storage.googleapis.com/workbox-cdn/releases/5.1.2/workbox-sw.js');
!function(){"use strict";try{self["workbox:sw:5.1.2"]&&_()}catch(t){}const t={backgroundSync:"background-sync",broadcastUpdate:"broadcast-update",cacheableResponse:"cacheable-response",core:"core",expiration:"expiration",googleAnalytics:"offline-ga",navigationPreload:"navigation-preload",precaching:"precaching",rangeRequests:"range-requests",routing:"routing",strategies:"strategies",streams:"streams"};self.workbox=new class{constructor(){return this.v={},this.t={debug:"localhost"===self.location.hostname,modulePathPrefix:null,modulePathCb:null},this.s=this.t.debug?"dev":"prod",this.o=!1,new Proxy(this,{get(e,s){if(e[s])return e[s];const o=t[s];return o&&e.loadModule(`workbox-${o}`),e[s]}})}setConfig(t={}){if(this.o)throw new Error("Config must be set before accessing workbox.* modules");Object.assign(this.t,t),this.s=this.t.debug?"dev":"prod"}loadModule(t){const e=this.i(t);try{importScripts(e),this.o=!0}catch(s){throw console.error(`Unable to import module '${t}' from '${e}'.`),s}}i(t){if(this.t.modulePathCb)return this.t.modulePathCb(t,this.t.debug);let e=["https://storage.googleapis.com/workbox-cdn/releases/5.1.2"];const s=`${t}.${this.s}.js`,o=this.t.modulePathPrefix;return o&&(e=o.split("/"),""===e[e.length-1]&&e.splice(e.length-1,1)),e.push(s),e.join("/")}}}();

const offlineFallbackPage = "offline.html";

self.addEventListener("message", (event) => {
  if (event.data && event.data.type === "SKIP_WAITING") {
    self.skipWaiting();
  }
});

self.addEventListener('install', async (event) => {
  event.waitUntil(
    caches.open(CACHE)
      .then((cache) => cache.add(offlineFallbackPage))
  );
});

if (workbox.navigationPreload.isSupported()) {
  workbox.navigationPreload.enable();
}

workbox.routing.registerRoute(
  new RegExp('/*'),
  new workbox.strategies.StaleWhileRevalidate({
    cacheName: CACHE
  })
);

self.addEventListener('fetch', (event) => {
  if (event.request.mode === 'navigate') {
    event.respondWith((async () => {
      try {
        const preloadResp = await event.preloadResponse;

        if (preloadResp) {
          return preloadResp;
        }

        const networkResp = await fetch(event.request);
        return networkResp;
      } catch (error) {

        const cache = await caches.open(CACHE);
        const cachedResp = await cache.match(offlineFallbackPage);
        return cachedResp;
      }
    })());
  }
});