Point taken, then let me rephrase that.

Threads we can fire and forget. Threads we can start "inside" our script and let them work while we do other stuff.

  myfunnyfunc = function(){/* do long funny stuff */}
  mycallback  = function(){/* do something when done */}
  
  mythread = new Thread(myfunnyfunc,mycallback);

Asynchronous like xmlhttprequest, just a way to replace the "settimeout" hack.