It’s not elegant, but there is a way to do type checking in CoffeeScript: http://coffeescript.org/#type-annotations

This is cool! That being said, it would be very nice to have (optional) syntactically more beautiful type annotation. I assume Flow must be compatible with regular javascript, but CoffeeScript could take more flexible approach. I have no idea what the actual syntax could be, though.

Thanks for the link. :)

But wow, "not elegant" is an understatement.