If you run an app with flutter run -d chrome --web-experimental-hot-reload, change a file, and then do a hot restart, you'll see that file's JS code file being loaded with a gen=1 suffix. You'll also see the old file in the sources tab.

This is confusing to users and doesn't actually do anything. It was intended to help with cache-busting, but that was for a multi-app scenario that Flutter tools does not come across.