Great examples, thanks!! I typed them all into the TypeScript playground.

I agree this is weird, and seems to follow from TypeScript's heritage as "trying to describe whatever dynamic JS does"

I mean that's probably why I didn't use it for >10 years (in addition to its JS heritage). But I did find that there is an interesting subset, at least for playing around.

I think the JSON.parse() issue is fundamental -- it's not clear what they could have done better, and static languages don't really do better. There is a fundamental problem there -- type systems are interior to a process, while data is exterior (https://www.oilshell.org/blog/2023/06/ysh-design.html)

I'm going to read this static TypeScript paper -- https://www.microsoft.com/en-us/research/publication/static-... Hopefully that's a sound subset :)