Webworkers, concurrency and other APIs

Hi, I have realized that the SpiderMonkey engine running on CodingGame doesn’t have many of the APIs I’m used to like Window.performance or Webworkers and these can be really useful when coding AIs in JavaScript. Is there documentation on what APIs are actually available? I’m especially interested in figuring out how to do the equivalent of Webworkers and do computation on more than one thread.