In Java or C++, there's a reasonable expectation that common popular libraries will keep getting updated for quite a while after you start using them... mindshare doesn't hemorrhage rapidly.

Not remotely true with JavaScript. Something which got 2k stars on gitub this year might be on the way out in a year, and you'll be stuck figuring out whether it still works with the new version of d3.js, or on the newest Chrome... and if it doesn't you have to either move on or fix it yourself.