Partly. You can define them if you want it. You can even add type support with FB Flow.

CS developers sometimes define variables because of hoisting.

Obviously, variables are defined. In CS they are simply defined for you automatically. That said, you can obviously do it yourself if you want. But you will not be able to use additional tooling around `let` and `const`

Can one use FB flow with CoffeeScript? Comments I saw on github indicated that the CS compiler mangled it, I think due to how functions are named and stripping comments?