Typescript type system is not that great to use. I've spent way too much time writing definitions for dependencies in JS or chasing bugs that the compiler should've caught (just because someone, in some layer used an any).

It's also quite slow to parse, making for a not great developer experience. One of Deno's priorities was in fact to rewrite the TS parser to speed it up.

Dyon looks nice and it's definitely a more rusty alternative.