Immediately returning response

sw.js

this.addEventListener('fetch', function(event) {
  var cachedResponse = caches.match(event.request).catch(function() {
    return event.default().then(function(response) {
      // With the assumption that this is an async operation...
      // (who reads specs anyway, and besides it's returning a promise) 
      // ...store the response to the cache in parallel.
      caches.get('v1').then(function(cache) {
        cache.put(event.request, response.clone());
      });  
      
      // Return the response immediately, without waiting for the cache write operation to finish
      return response;
    });
  }).catch(function() {
    return caches.match('/sw-test/gallery/myLittleVader.jpg');
  });
    
  event.respondWith(cachedResponse);
});