open method
The open() method of the
CacheStorage interface returns a Promise that resolves to
the Cache object matching the cacheName.
You can access CacheStorage through the Window.caches property in
windows or through the WorkerGlobalScope.caches property in workers.
Note: If the specified Cache does not exist, a new cache is created with that
cacheNameand aPromisethat resolves to this new Cache object is returned.
Implementation
external JSPromise<Cache> open(String cacheName);