title: Service worker is caching files but fetch event is never fired
body: <p>I have just attempted to implement service workers to cache some JSON files and other assets on a static site (running on localhost chrome Version 47.0.2526.73 (64-bit)). Using cache.addAll() I have added my files to the cache, and when I open the resources tab in chrome, and click on cache storage, all the files are listed. </p>
  
  <p><a href="https://i.stack.imgur.com/SBp4R.png" rel="noreferrer"><img src="https://i.stack.imgur.com/SBp4R.png" alt="screenshot json files shown in cache"></a></p>
  
  <p>The issue I am having is that my service worker is listed as "activated" and "running" in chrome://service-worker-internals however, I cannot determine if the worker is actually intercepting the requests and serving up the cached files. I have added the event listener and even when I console log the event in the service workers dev tools instance, it never hits the break point: </p>
  
  <pre><code>this.addEventListener('install', function(event) {
    event.waitUntil(
      caches.open('v1').then(function(cache) {
        console.log(cache);
        return cache.addAll([
          '/json/0.json',
          '/json/1.json',
          '/json/3.json',
          '/json/4.json',
          '/json/5.json',
        ]);
      })
    );
  });
  
  this.addEventListener('fetch', function(event) {
    console.log(event);
    var response;
    event.respondWith(caches.match(event.request).catch(function() {
      return fetch(event.request);
    }).then(function(r) {
      response = r;
      caches.open('v1').then(function(cache) {
        cache.put(event.request, response);
      });
      return response.clone();
    }).catch(function() {
    }));
  });
  </code></pre>
  
  <p>Basically I am running through things exactly as described in HTML5 rocks service workers intro, but I am pretty sure that my assets aren't being served from the cache. I've noted that assets served up from a service worker are noted as such in the network tab of devtools in the size column by indicating 'from service workers'.</p>
  
  <p>It just seems as if my code is no different than the examples but it's not ever hitting the fetch event for some reason. Gist of my code: <a href="https://gist.github.com/srhise/c2099b347f68b958884d" rel="noreferrer">https://gist.github.com/srhise/c2099b347f68b958884d</a></p>