So there will be an "official" JS VM but there will be no actual compilation. Title should be updated IMHO.
You enter code using the Processing language, and if you've selected the JavaScript "mode" it will output JavaScript that uses processing.js and canvas.
Prior to 2.0 the modes were "standard" (i.e. Java byte code) and "android" (Dalvik byte code, I presume, since you get an apk file).