Nice. If you want to implement another feature: see the error response. My server returned 428, but I couldn't see the contents nor header, only a generic "preview".
~~I think axios can. Its API is similar to fetch, except for the return status. You could also manipulate the cookies before and after transmission, but that might be messy when you hit the browser's cookie limits.~~
Scratch that. I wasn't thinking clearly. I ran the call from restfox.dev, and it's another domain, of course. You'd need to write your own http client to get around it.