[patates]

You can use discriminated unions with TS (https://antman-does-software.com/typescripts-discriminated-u...), and you can even parse them from unknown data using tools like zod (https://zod.dev/?id=discriminated-unions), io-ts, or the likes.

I can't think of anything I can do in .NET (which has runtime types) that I can't do in TS with the help of a library or two.

[sa46]

> I can't do in TS with the help of a library or two.

Libraries like io-ts and zod embed the type information into JavaScript, so the information is available at runtime but only for wrapped types. If TypeScript provided runtime type information, such libraries wouldn't be necessary.