sw.js

var APP_PREFIX = 'ApplicationName_'     // Identifier for this app (this needs to be consistent across every cache update)
var VERSION = 'version_01'              // Version of the off-line cache (change this value everytime you want to update cache)
var CACHE_NAME = APP_PREFIX + VERSION
var URLS = [                            // Add URL you want to cache in this list.
  '/SWTest/',                     // If you have separate JS/CSS files,
  '/SWTest/index.html'            // add path to those files here
]

let outgoingPort;
self.addEventListener('message', function (e) {
  if (e.data && e.data.type === 'INIT_PORT') {
    outgoingPort = e.ports[0];
  }
});

// Respond with cached resources
self.addEventListener('fetch', function (e) {
  if (outgoingPort) {
    outgoingPort.postMessage({ message: " fetch: " + e.request });
  }
  if (e.request.url.includes("testImage.jpg")) {
    let newRequest = new Request("https://paultiarks.github.io/SWTest/testImageTwo.jpg")
    e.respondWith(fetch(newRequest))
  }
})

// Delete outdated caches
self.addEventListener('activate', function (e) {
  if (outgoingPort) {
    outgoingPort.postMessage({ message: "activated" });
  }
})