A service worker that returns assets from cache and refreshes them afterwards

sw.js

// Pre-fetch the assets when the service worker is installed
self.addEventListener('install', function(evt) {
  evt.waitUntil(precache());
});

function precache() {
  return caches.open(‘your-app-name-cache’).then(function (cache) {
    // list all your assets in the array
    return cache.addAll([
      '/index.html',
      '/js/bundle.js',
      '/public/css/style.css',
      '/manifest.json',
      '/sw.js',
      'https://api.digitransit.fi/routing/v1/routers/hsl/bike_rental'
    ]);
  });
}

// Everytime the application requests a resource, return it from cache 
// and try to refresh it afterwards
self.addEventListener('fetch', function(evt) {
  evt.respondWith(fromCache(evt.request));
  evt.waitUntil(update(evt.request));
});
 
function fromCache(request) {
  return caches.open(‘your-app-name-cache’).then(function (cache) {
    return cache.match(request).then(function (matching) {
      return matching || Promise.reject('no-match');
    });
  });
}

function update(request) {
  return caches.open(‘your-app-name-cache’).then(function (cache) {
    return fetch(request).then(function (response) {
      return cache.put(request, response);
    });
  });
}