I think it's quite reasonable to want to respond to a back gesture to cancel a modal that asks if you're sure about deleting <some resource>. You could render everything server side to get website-like navigation, but for these things JS is probably one of the better mechanisms to make user interaction more pleasing.
This stuff should absolutely be kept away from news sites, blogs and other web resources because they're awful enough already with their constant popups about signing up for newsletters, accepting notifications and pitiful pleas to use their app. For your average PWA, though, this is definitely a bad thing.