I mean, there's lots of fun stuff in Ruby core (and a huge amount many Ruby devs are often unaware of) but if I'm ultimately still working in JavaScript, this hits a lot of walls. ES6 will allow something like method_missing, but we're not there yet.
Also: blocks.
Blocks in RubyJS translate to functions (as the last parameter). They work pretty much the same in RubyJS. You can break out of a loop using a breaker object.
It's not about the Ruby object model and metaprogramming capabilities but about the core library.
Especially as Ruby developer if you switch to JS you spend an inordinate amount relearning a new (IMO not so convenient) standard library.
Also RubyJS methods are chainable by design (methods return other RubyJS objects. So you can write:
R([1,2,3]).map(...).join(',').capitalize().ljust(50)But the pricing is no good. It's $190/dev for alpha software with no support. That's just not going to cut it.