The function expects a string and does things in the function body which converts the object into a string.

... These are different words that describe exactly what I'm saying. I'm saying: in the place where there should be a string argument, because the function expects one, there is not a string argument, but a number argument. (Not an object like you keep saying.)

I know all that stuff about dynamically typed languages. I'm just saying that the function is being used indirectly here.