Comment by IshKebab

There wouldn't be any benefit. It's not sound so it can't really be used to improve performance.

There was a proposal to support TypeScript syntax, but ignore the actual types (this is basically how Python works). That would be kind of nice because you can skip the compilation step completely (less faff for small projects), but I don't think it went anywhere... or if it is it's getting there at a snail's pace:

https://github.com/tc39/proposal-type-annotations