Interesting, didn't know about this variable.
But careful, JScript v5.x is still at best ES3, not JavaScript/EcmaScript/ES v5. JScript's internal versioning goes up to 5.8 but is still a Microsoft proprietary implementation of ES3 from 1999. I don't think you would have anything less than v5.6 or 5.8 even on most recent Windows machines. Hoping that DOpus devs will give us jscript9.dll or chakra.dll some time as I posted elsewhere.