Leveraging a related answer:
The following blog post lists some recent packages: http://jgoodall.me/posts/2012/02/01/javascript-statistical-libraries/
As mentioned by others, native JS is a far cry from R, which web-wise has progressed from RApache (http://rapache.net/) to shiny (http://www.rstudio.com/shiny/). The latter uses node.js server-side, so this is quite promising. Of course both approaches will require you to code stats in R server-side, instead of using JS either on client or server.
Marc
