prevent config from being cached but preserve offline capability

public/service-worker.js

@@ -1,7 +1,7 @@
 const cacheVersion = 'v1.9.4';
 const cacheTitle = `pairdrop-cache-${cacheVersion}`;
 const forceFetch = false; // FOR DEVELOPMENT: Set to true to always update assets instead of using cached versions
-const urlsToCache = [
+const relativePathsToCache = [
     './',
     'index.html',
     'manifest.json',
@@ -36,28 +36,44 @@ const urlsToCache = [
     'lang/ru.json',
     'lang/zh-CN.json'
 ];
+const relativePathsNotToCache = [
+    'config'
+]
 
 self.addEventListener('install', function(event) {
   // Perform install steps
     event.waitUntil(
         caches.open(cacheTitle)
             .then(function(cache) {
-                return cache.addAll(urlsToCache).then(_ => {
-                    console.log('All files cached.');
-                });
+                return cache
+                    .addAll(relativePathsToCache)
+                    .then(_ => {
+                        console.log('All files cached.');
+                    });
             })
     );
 });
 
 // fetch the resource from the network
 const fromNetwork = (request, timeout) =>
-    new Promise((fulfill, reject) => {
+    new Promise((resolve, reject) => {
         const timeoutId = setTimeout(reject, timeout);
-        fetch(request).then(response => {
-            clearTimeout(timeoutId);
-            fulfill(response);
-            update(request).then(_ => console.log("Cache successfully updated for", request.url));
-        }, reject);
+        fetch(request)
+            .then(response => {
+                clearTimeout(timeoutId);
+                resolve(response);
+
+                if (doNotCacheRequest(request)) return;
+
+                update(request)
+                    .then(() => console.log("Cache successfully updated for", request.url))
+                    .catch(reason => console.log("Cache could not be updated for", request.url, "Reason:", reason));
+            })
+            .catch(error => {
+                // Handle any errors that occurred during the fetch
+                console.error(`Could not fetch ${request.url}. Are you online?`);
+                reject(error);
+            });
     });
 
 // fetch the resource from the browser cache
@@ -68,17 +84,32 @@ const fromCache = request =>
             cache.match(request)
         );
 
+const rootUrl = location.href.substring(0, location.href.length - "service-worker.js".length);
+const rootUrlLength = rootUrl.length;
+
+const doNotCacheRequest = request => {
+    const requestRelativePath = request.url.substring(rootUrlLength);
+    return relativePathsNotToCache.indexOf(requestRelativePath) !== -1
+};
+
 // cache the current page to make it available for offline
-const update = request =>
+const update = request => new Promise((resolve, reject) => {
+    if (doNotCacheRequest(request)) {
+        reject("Url is specifically prevented from being cached in the serviceworker.");
+        return;
+    }
     caches
         .open(cacheTitle)
         .then(cache =>
-            fetch(request)
-                .then(async response => {
-                    await cache.put(request, response);
+            fetch(request, {cache: "no-store"})
+                .then(response => {
+                    cache
+                        .put(request, response)
+                        .then(() => resolve());
                 })
-                .catch(_ => console.log(`Cache could not be updated. ${request.url}`))
+                .catch(reason => reject(reason))
         );
+});
 
 // general strategy when making a request (eg if online try to fetch it
 // from cache, if something fails fetch from network. Update cache everytime files are fetched.