fix(sw): return inner promise in activate cache cleanup (webpack#7928)

The cache.keys().then() chain inside the activate event handler
was not being returned, so event.waitUntil() resolved immediately
with undefined before any stale cache entries were deleted.

This meant old cache entries from previous deployments would
accumulate in users' browsers silently with no guarantee of cleanup.

Fix by returning the inner promise chain and using Promise.all()
to delete stale entries in parallel, ensuring event.waitUntil()
only resolves once all deletions are complete.

Author: ryzrr

src/sw.js

@@ -38,16 +38,18 @@ self.addEventListener("install", (event) => {
 self.addEventListener("activate", (event) => {
   // - [x] clean up outdated runtime cache
   event.waitUntil(
-    caches.open(cacheName).then((cache) => {
+    caches.open(cacheName).then((cache) =>
       // clean up those who are not listed in manifestURLs
-      cache.keys().then((keys) => {
-        for (const request of keys) {
-          if (!manifestURLs.includes(request.url)) {
-            cache.delete(request);
-          }
-        }
-      });
-    }),
+      cache
+        .keys()
+        .then((keys) =>
+          Promise.all(
+            keys
+              .filter((request) => !manifestURLs.includes(request.url))
+              .map((request) => cache.delete(request)),
+          ),
+        ),
+    ),
   );
 });