Include core assets in serviceworker cache (#11559)

app/views/service_worker/index.js.erb

@@ -137,6 +137,22 @@
       return;
     }
 
+    // Fetch and/or JS and CSS assets for better persistence than memory cache.
+    if (url.pathname.startsWith("/assets/") || url.pathname.startsWith("/packs/")) {
+      event.respondWith(
+        caches.open(staticCacheName).then(function (cache) {
+          return cache.match(event.request).then(function (response) {
+            return (
+              response ||
+              fetch(event.request).then(function (response) {
+                cache.put(event.request, response.clone());
+                return response;
+              })
+            );
+          });
+        })
+      );
+    }
     if (url.origin === location.origin) {
       if (event.clientId === "" && // Not fetched via AJAX after page load.
         event.request.method == "GET" && // Don't fetch on POST, DELETE, etc.
@@ -187,6 +203,22 @@
             "/shell_bottom",
           ]));
       }
+
+      // Periodically delete assets when they pile up
+      if (Math.random() > 0.97) {
+        caches.open(staticCacheName).then(function(cache) {
+          cache.keys().then(function(keys) {
+            if (keys.length > 100) {
+              keys.forEach(function(r) {
+                if (r.url.includes("/assets/") || r.url.includes("/packs/")) {
+                  cache.delete(r);
+                };
+              });
+            }
+          });
+        });
+      }
+
     }
   });
 <% end %>