OK, so this blog is starting to look like the Steve Yegge Fan Club, and I’m only 3 posts in. Lucky for me, I don’t care.
Anyway, I found out a lot. ES4 is already available, (more or less, as the spec isn’t finalized) in Adobe’s ActionScript 3 (AS3). Yes, the language used for Flash. Adobe built a virtual machine for it, codename Tamarin , aka AVM2. It’s been embedded in Flash 9, and it’s supposed to be wicked fast. It’s also been open sourced and donated to Mozilla, so it should show up in Firefox 3.  Frank Hecker wrote a nice piece on what impact this will have.
So soon you’ll be able to use the same language for Flash apps, Flex 2 apps (which is a lot more up my alley), and AJAX. That’s a big motivator to learn it.
- There appears to be only one active committer, and just a few other helpers. Apparently Sun does not have any engineers devoted to Rhino.
- Modifying Rhino to handle ES4 is a daunting task. Rhino was initially a straight port of Spidermonkey, which was written in C.
- The other option suggested is creating a straight port of Tamarin. Tamarin was written in AS3, essentially JS2, which should be easier to port to Java than C was. But it’s 135,000 lines! And in a much terser language than Java! So who knows how many lines the port will end up being. An AS3-to-Java compiler seems like it would take less time, but that still sounds like a major effort.
I’ve also seen a couple instances (PHP, Python) where someone connected Java to a native implemenation of a language. Perhaps they could do that with Tamarin, although I wonder about the performance. Would it be better than a Java implementation, or would the overhead hurt it too much?
So I’m bummed, as I’m looking for something to help me script Java (actually, replace it in the middle – and possibly presentation – tier), but I don’t want to choose a dead platform. To use JS2 server-side I’d have to give up Java altogether, and that seems like cutting off my nose to spite my face, or throwing the baby out with the bath water, or some other such calamity. There are just too many Java FOSS libraries, which solve really hard problems, that I’d have to give up.
So I’m going to have to size up JRuby some more, and perhaps do a bit more digging on ES4, before I make any rash decisions. Procrastination wins again!
 BTW, the presentation uses some new HTML/CSS/JS document format to replace PowerPoint, and you have to point your mouse in the lower right to pop up the controls. Crazy frustrating if you don’t know that.
 If Microsoft was smart, they’d use it for IE8, assuming that’s legal and wouldn’t cause Mr. Gates to have an aneurysm.