Javascript and Ruby are of an age, both first released in 1995. Javascript has always supported all of the use cases described here for Ruby, until very recently with exactly one syntactic convention for argument passing. If you want keyword arguments, pass an object; if you want to pass a function, pass a function.
That's simpler to understand because there is less to understand, with these capabilities composed from extant syntax rather than having been invented as one-offs that require being learned and understood as such, each hedged around with its own special cases and failures to generalize - if that were not the case, the article here under discussion and all others like it would never have needed writing in the first place.
I realize describing Javascript as "well designed" will be controversial, and certainly it has not been without its share of flaws: loose equality and IEEE 754 float behavior come most quickly to mind, along with the lack of a general conditional expression. I am comfortable with describing Javascript as better designed than Ruby, though. Certainly it is far more ergonomic.
Good engineering above all else is, as much as possible, simple: it can't help being about as complex as the domain it addresses, but any complication beyond that represents an error of design. Programming a general-purpose computer is an arbitrarily complex domain, which gives all the more point to the need for simplicity in design: the user of the tool has enough to think about already, and should insofar as possible not also be forced to manage unnecessary complexity in tooling. Under such a metric, that Ruby needs three kinds of calling conventions to accomplish what Javascript does with one is already enough to demonstrate that Ruby's design is lacking.