If you only have a single file that has a limited set of responsibilities (e.g., just a small tool) and is not shared / distributed then JS may still be okay, otherwise always go for TypeScript.
Honestly, TypeScript never slows me down. The enhanced completion / IDE knowledge, compile-time type checking, and transpilation supporting newer ES features + React is a huge boost.
If you only have a single file that has a limited set of responsibilities (e.g., just a small tool) and is not shared / distributed then JS may still be okay, otherwise always go for TypeScript.
Honestly, TypeScript never slows me down. The enhanced completion / IDE knowledge, compile-time type checking, and transpilation supporting newer ES features + React is a huge boost.