Which JavaScript (ECMAScript) version does Java's Rhino implementation implement (and what's the update policy?)

Which version of the ECMAScript standard does Java's JavaScript engine Rhino support, how much work is going into fixing bugs and keeping the implementation in sync with the latest standardized version?

Note: this question is far out of date and not useful.

The question was asked in 2011, and the JDK (as of late fall 2015) no longer ships with Rhino at all; the question referred to JDK 1.6, though JDK 1.7 was released a couple weeks afterwards.

Nashorn in JDK 1.8 60 supports ES 5.1, possibly with a couple of ES2015 extensions; it's hard to find an explicit compatibility claim from Oracle sources. Supposedly, JDK 9 Nashorn is supposed to "fully support" ES2015, but again I've been unsuccessful locating official sources.

edit — note that even Nashorn is going to be unsupported soon; JDK 13? 14? Something like that.

Below is the original answer.

Rhino in the shipped JDK (from Sun) is version 1.6R2. It's ancient. Supposedly it's going to be updated in the 1.7 release.

You can always download Rhino from Mozilla and use their integration facility. I've used the Sun one, and while it's dirt simple it leaves a lot to be desired.

edit — as to which ECMAScript standard it is, well, it's a Mozilla release so they've got their own modifications. However 1.6R2 is so old that it doesn't even have things like ".forEach()".