I have previously pointed out that there is nothing magical about Ruby or Rails.

John Lam:

Steve decided to do what any other frustrated programmer would do: he ported Rails to JavaScript. Line by line. In 6 months.

I'm just glad I didn't have to put in the 2,000 hours of coding myself to prove the point.

I will note that I don't agree with Steve's assertion that JavaScript is the Next Big Language, as I disagree with the entire premise of the question itself.

Update: More on Rhino on Rails from Steve himself.