As libraries seem to evolve, making it easier to program, it seems people are using JS for more things that Java would have been used for in its heyday.
That said, there are many performance problems with JS that we are aware of and just one of them is the ability to optimize runtime using threads.
I saw this: Why doesn't JavaScript support multithreading?, but that was answered 3-4 years ago (and a lot changes in a year, let alone 3-4). With HTML5 growing fast, I’m even more curious if this has been given more consideration.
You should ask, ECMA TC39, they own ECMAScript.
But the short answer will be no, if you have long-running scripts that you want to “spawn a new thread” for you should check out WebWorkers, they run in their own context and technically on another thread.