service-worker.js

self.addEventListener('install', function (event) {
  console.log('Install');
});

self.addEventListener('activate', function (event) {
  console.log('Activate');
});

var cacheName = 'railroutersg-v2';
caches.delete('railroutersg-v1'); // Delete the old one
var successResponses = /^0|([123]\d\d)|(40[14567])|410$/;

function fetchAndCache(request) {
  return fetch(request.clone()).then(function (response) {
    if (
      request.method == 'GET' &&
      response &&
      successResponses.test(response.status) &&
      (response.type == 'basic' ||
        /\.(js|png|ttf|woff|woff2)/i.test(request.url) ||
        /fonts\.googleapis\.com/i.test(request.url))
    ) {
      console.log('Cache', request.url);
      caches.open(cacheName).then(function (cache) {
        cache.put(request, response);
      });
    }
    return response.clone();
  });
}

function cacheOnly(request) {
  return caches.open(cacheName).then(function (cache) {
    return cache.match(request);
  });
}

// Fastest strategy from https://github.com/GoogleChrome/sw-toolbox
self.addEventListener('fetch', function (event) {
  var request = event.request;
  var url = request.url;
  event.respondWith(
    new Promise(function (resolve, reject) {
      var rejected = false;
      var reasons = [];

      var maybeReject = function (reason) {
        reasons.push(reason.toString());
        if (rejected) {
          reject(new Error('Both cache and network failed: "' + reasons.join('", "') + '"'));
        } else {
          rejected = true;
        }
      };

      var maybeResolve = function (result) {
        if (result instanceof Response) {
          resolve(result);
        } else {
          maybeReject('No result returned');
        }
      };

      fetchAndCache(request.clone()).then(maybeResolve, maybeReject);
      cacheOnly(request).then(maybeResolve, maybeReject);
    }),
  );
});