Yeah, this is an important question. I don't have answer for you and neither do the people in charge of the fetch API. It's an issue with promises not being cancelable. There's probably a reasonable argument that promises just aren't that great because you can only resolve or reject.

Personally I don't see a huge problem with either resolving or rejecting with a message about the cause of the result. Others see it differently but they haven't been able to make any progress on a major problem.

If you want to avoid this altogether there's no reason why you can't use a different library.

I don't have an answer for you but I dislike that Fetch() doesn't currently have any support for progress events. So say good-bye to your file-upload progress bar!