I just learned about jrunscript, which is a Javascript console and interpreter distributed with Java 6, so chances are you already have it. In fact, it is a general purpose interpreter and you can select another language with the -l flag if it is in the classpath. The -q flag lists the currently installed languages. This is what I got on OS X 10.6.4:

$ jrunscript -q
Language ECMAScript 1.6 implemention "Mozilla Rhino" 1.6 release 2
Language AppleScript 2.1.2 implemention "AppleScriptEngine" 1.0

Pretty cool and it means you don’t even need to download Rhino like I mentioned in my previous blog post of Javascript consoles.