When 7 KB Equals 7 MB

While testing a progressive web app for one of our clients, I bumped into a suspicious error in the browser console:

DOMException: Quota exceeded.

After browsing the app a few more times, it became clear the error would occur after a small number of images were added to the cache storage by the service worker. Looking in the Chrome DevTools Application tab, the cache storage was indeed over capacity.

Chrome DevTools showing over-capacity cache storage.
Chrome DevTools showing over-capacity cache storage.

How could this be? There were only ~15 images in the cache storage. Something was off.

What I found could significantly impact your progressive web app—particularly if you use a CDN on a different domain for your assets.


If you are building a progressive web app and are experiencing bloated cache storage when your service worker caches static assets served from CDNs, make sure the proper CORS response header exists for cross-origin resources, you do not cache opaque responses with your service worker unintentionally, you opt-in cross-origin image assets into CORS mode by adding the crossorigin attribute to the <img> tag.

See the source link for more details.