Agreed that actually doing the transformations is a bit of a mug's game. However, TypeScript's type system treats class definitions interestingly, particularly

Agreed that actually doing the transformations is a bit of a mug's game. However, TypeScript's type system treats class definitions interestingly, particularly around metadata. You can attach validation metadata to a class and pass plain objects around that structurally match that class so long as you don't define methods or a constructor. As mentioned in my sibling comment to yours, I do this to define DTOs that are then expressed in JSON Schema and passed through ajv, and it's pretty slick. The objects being used are all just JavaScript objects, the class is just being used as a metadata holder and something you can reference/get via `design:type`/`design:paramtype`/`design:returntype`.