WindowTimers.setTimeout() has the following signature:

def setTimeout(handler: js.Any, timeout: js.Any, args: js.Any*): Int = ??? 

Some users (including myself) ran into a problem passing a block instead of a lambda. It would be helpful if the compiler could catch this on-the-fly. Therefore, I would advise changing it to:

def setTimeout(handler: () => Unit, timeout: Int): Int = ??? 

MDN also doesn't specify the additional parameters, which appear to be safe to drop.

In the unlikely event that the user wants to use the untyped version, he can just resort to js.Dynamic.global.setTimeout().