[catfishx]

AFAIK Typescript has no runtime impact on performance, the transpiled JS should be equally fast as the handwritten code

[AgentME]

I think they mean the performance of VSCode editing a project with Typescript code in it. There's the runtime cost of VSCode checking the Typescript, providing intellisense, etc. (Not that I've ever had that runtime cost be noticeable to me. Maybe it's a real issue on certain codebases or workflows.)