what is the engine of chess.com analysis? does anybody know that?

and who knows what the best engine for analysis?

I believe it's stockfish js.6. Right?

It doesn't matter, because it doesn't run on your computer's resources, instead the chess.com servers dole out an itsy bitsy teeny weenie bit of processing power.  At least, that is my understanding.  I am not sure why it is done this way, as free competitors to chess.com run the analysis off your personal computer, resulting in vastly better analysis.  Maybe there is a good reason for it, but the cynic in me thinks they deliberately hobble the free analysis to give another reason to upgrade to premium.  

There is a stockfish 8 now, right? Shouldn't that be better?

But the processing still needs to be based on some code (whether locally or on chess.com's servers). I believe the engine is stockfish, but let me know if I'm not correct.

I believe that it is some version of stock fish and that different engines are quite different and can have ratings that differ by up to a point or two. 

The current one is, but when this was started in 2015, the v2 engine may have been something else.

For v3, premium can do deeper analysis but a lot of people use their own engines for deep analysis on a local machine.

Anyways, you can download the Arena Chess GUI and Stockfish 8 both for free, and get arguably the best analysis in the world. 

Thanks for the information captain obvious.