[mnarayan01]

> you cannot cancel the actual (OS controlled) asynchronous operation

This is way too broad a claim. If I do something like:

  (sleep 1 ; echo "done") &
  kill $!

I'm pretty clearly "cancelling the actual (OS controlled) asynchronous operation". Now it may have done some sleeping at that point, and if you replace the sleep with something that has side-effects, then some of those side-effects may have occurred, but the operation is still being "cancelled".

Obviously it's not the case that every operation can be (meaningfully) cancelled, but some can. This is even more true when you consider that when you're using JS, you're generally way above the OS level. XMLHttpRequest has an abort() method for a reason: The underlying socket request may be queued up based on your browser's connection limits and, even if it's kicked off, your browser is going to have multiple opportunities to abort the process even if none of the underlying sub-operations can be preemptively cancelled.