generally you are right, it would be far easier to hide these kind of choices if the language allowed it. However currently javascript has a purely event drive

generally you are right, it would be far easier to hide these kind of choices if the language allowed it. However currently javascript has a purely event driven model and this means that you have trouble fitting in even a purely CPU bound computation, as it would block the responsiveness of your UI (or other concurrent requests if your are doing server side JS). That's why there was a need for creating something like WebWorkers.