Seems to me that using the functional style it's really important to document the types (done in the article with the //+ lines).

Otherwise it will be hard to make the types line up.

Also there are functions in javascript which do different things depending on what the type of the argument is (or do different things depending on how many arguments are passed in; those kinds of functions always have irked me), so it would be hard to document exactly what the "type" of those functions are.