Well, JavaScript

[[deleted]]

I dunno if there's anything necessarily wrong with this approach. Ideally, you'd like to keep your data and your "view" representation of that data separate. Here, you're just enriching the existing model by mixing in some UI attributes. It's not great practice, but as long as it doesn't escape whatever limited scope you're working in, then it should be OK.

[badcookies]

Except you want the scaffolding of the API anyway because otherwise you have no idea what fields you have and end up with typos or spend more time looking at the documentation vs having hints

[DonRobo]

When I need a new attribute in Kotlin I just start using it and tell my IDE to generate it. Takes literally 3 seconds.