Rhino is About to Get a Lot Faster
And on the server side, it has become popular because runtimes now perform well and there's a lot of libraries written for client-side that are applicable to the server as well. ...
Finally we asked Nutter how Rhino compared with the challenges thrown up by JRuby from an implementation point of view. Nutter responded:
Rhino may actually be an easier target in many ways, since it does not have some of Ruby's wilder features. However, it presents an interesting challenge in that its prototype-based object model leaves no clear location to store method table caches as is the case in Ruby. Techniques used by V8 and John Rose's "DavinciMonkey" (an early attempt at invokedynamic-based Rhino) -- such as generating synthetic classes as prototypes are modified -- should make it easier to deal with Rhino's more fluid type structure.
Sounds very exciting