Signature of lambda return types in TypeScript

In the TypeScript below both functions are the same, except that I'm trying to explicitly declare the return type in demoTwo. The return type is a function which itself takes a function as input. My question is why do I have to give the parameter name represented by whyThis, given that it will never be used? The code will not compile without something in that position.

function demoOne() {
    return function(input: () => string) : void {
        var result = input();
        console.log("Foo:",result);
    }
}

function demoTwo(): (whyThis:() => string) => void {
    return function(input: () => string) : void {
        var result = input();
        console.log("Bar:",result);
    }
}

var sampleInput = () => "wibble";
demoOne()(sampleInput);
demoTwo()(sampleInput);

To be clear what I'm asking here's the equivalent code in Scala:

object Program {
  def demoTwo(): (() => String) => Unit = {
    def tmp(input: () => String): Unit = {
      val result = input()
      println("Bar: " + result)
    }
    return tmp
  }
  def main(args: Array[String]): Unit = {
    val sampleInput = () => "wibble"
    demoTwo()(sampleInput)
  }
}

If we set the declarations of demoTwo side by side we have:

function demoTwo(): (whyThis:() => string) => void { //TS
def demoTwo(): (() => String) => Unit = { //Scala

The only major difference is that TS requires something at the whyThis position and Scala does not. Why should this be the case?