Very basic service worker for PWA apps (from the Google example code)

sw.js

if ('serviceWorker' in navigator) {
  window.addEventListener('load', function() {
    navigator.serviceWorker.register('/sw.js').then(function(registration) {
      // Registration was successful
      console.log('ServiceWorker registration successful with scope: ', registration.scope);
    }, function(err) {
      // registration failed :(
      console.log('ServiceWorker registration failed: ', err);
    });
  });
}

var CACHE_NAME = '001';
var urlsToCache = [
  '/',
];

self.addEventListener('install', function(event) {
  // Perform install steps
  event.waitUntil(
    caches.open(CACHE_NAME)
      .then(function(cache) {
        console.log('Opened cache');
        return cache.addAll(urlsToCache);
      })
  );
});

self.addEventListener('fetch', function(event) {
  // Only cache GET requests
  if(event.request.method === "GET"){
    event.respondWith(
      caches.match(event.request)
        .then(function(response) {
          // Cache hit - return response
          if (response) {
            return response;
          }

          return fetch(event.request).then(
            function(response) {
              // Check if we received a valid response
              if(!response || response.status !== 200 || response.type !== 'basic') {
                return response;
              }

              // IMPORTANT: Clone the response. A response is a stream
              // and because we want the browser to consume the response
              // as well as the cache consuming the response, we need
              // to clone it so we have two streams.
              var responseToCache = response.clone();

              caches.open(CACHE_NAME)
                .then(function(cache) {
                  cache.put(event.request, responseToCache);
                });

              return response;
            }
          );
        })
    );
  }
});