sw.js

//This is the "Offline copy of pages" service worker

//Install stage sets up the index page (home page) in the cache and opens a new cache
self.addEventListener("install", function(event) {
  var indexPage = new Request("index.html");
  event.waitUntil(
    fetch(indexPage).then(function(response) {
      return caches.open("pwabuilder-offline").then(function(cache) {
        console.log(
          "[PWA Builder] Cached index page during Install " + response.url
        );
        return cache.put(indexPage, response);
      });
    })
  );
});

//If any fetch fails, it will look for the request in the cache and serve it from there first
self.addEventListener("fetch", function(event) {
  var updateCache = function(request) {
    return caches.open("pwabuilder-offline").then(function(cache) {
      return fetch(request).then(function(response) {
        console.log("[PWA Builder] add page to offline " + response.url);
        return cache.put(request, response);
      });
    });
  };

  event.waitUntil(updateCache(event.request));

  event.respondWith(
    fetch(event.request).catch(function(error) {
      console.log(
        "[PWA Builder] Network request Failed. Serving content from cache: " +
          error
      );

      //Check to see if you have it in the cache
      //Return response
      //If not in the cache, then return error page
      return caches.open("pwabuilder-offline").then(function(cache) {
        return cache.match(event.request).then(function(matching) {
          var report =
            !matching || matching.status == 404
              ? Promise.reject("no-match")
              : matching;
          return report;
        });
      });
    })
  );
});