javascript - Service worker is caching files but fetch event is never fired

Question

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.

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:

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() {
  }));
});

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'.

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: https://gist.github.com/srhise/c2099b347f68b958884d

Answer 1

After looking at your gist and your question, I think your issue is with scoping.

From what I've determined with service workers(at least with static files), the service worker only has a maximum scope of the directory it is in. That is to say, it can't load files/requests/responses that are pulled from a location at or above its structure, only below.

For example, /js/service-worker.js will only be able to load files in /js/{dirName}/.

Therefore, if you change the location of your service worker to the root of your web project, the fetch event should fire and your assets should load from cache.

So something like /service-worker.js, which should be able to access the /json directory, since it is deeper than the service-worker.js file.

This is further explained here, in the "Register A service worker" section. https://developers.google.com/web/fundamentals/getting-started/primers/service-workers