I would venture to guess that interoperability with existing projects and services is important to some people. Also, there are Java libraries which are significantly better than their closest corresponding Node package.

Why would you code in Javascript on the JVM to begin with if you have existing projects and libraries written in java ? that's stupid. If the goal is async IO there is Vert.x and other non blocking servers already. Not even talking about cases when libs require C++ extensions... Can you code in Java on Nodyn? no

EDIT : seems to be built upon Vert.x ? you can already code in javascript with Vert.x

"that's stupid" is a pretty broad statement. There are many reasons why one may choose to write new software in JS while taking advantage of existing investment in Java. If it doesn't make sense for you, don't do it. But for many it may.

As for coding Java on Nodyn, well, yes you can. That's kind of the point in some ways. You can write Java, package it as a jar and access this from Nodyn. Nodyn itself does this for the Buffer implementation.

Yes, vert.x already supports JS (I maintain the mod-lang-js, mod-lang-rhino and mod-lang-dynjs language modules for vert.x). The idea behind Nodyn is to provide drop-in Node.js compatibility in the Vert.x environment.

But if you code JS for Vert.x, you're restricted to Vert.x for life.

This way you write JS for Node and you can run it under either Node or the JVM.

How much do you trust the nodejs driver compatibility layers for oracle and db2? How about generating Excel files? Nothing comes close to poi yet.

That said, I'd suggest running node wither a service oriented architecture if both were non-negotiable requirements.