I think it can write working TypeScript code, and it can write good TypeScript code if it is guided by a knowledgable programmer. It requires actually reviewing all the code and giving pointed feedback though (which at that point is only slightly more efficient than just writing it yourself).
> It requires actually reviewing all the code and giving pointed feedback though
Exactly. You can write good Typescript, no doubt, but LLMs cannot. This is not like some other languages where LLM generated code is actually consistently good without needing to become the author.