Yeah, found this out the hard way with customers complaining that they hit save, get an error code "0", and then couldn't save again because we had disabled the button after submitting.

Side rant: can I take a moment to call out WHATWG for deciding to specify that all networking errors in XmlHttpRequest get status: 0 and absolutely no explanation anywhere in the response object ( see https://fetch.spec.whatwg.org/#concept-network-error ), making it absolutely a nightmare to diagnose problems and support our users? I suppose in a world of fail whales and cute cat pics, leaving the user in the dark as to why something broke is now standard practice, but at least in those cases there's something server side to let techs know what's going on, but I get random calls from users complaining about this and the best I've got is that they tried to leave the page while the form was still saving (this triggers the error handler too since it's the exact same code) or their internet connection dropped ever so briefly because the next words out of their mouth when they say that is "but I can view other websites".