In NodeJS: is it possible for two callbacks to be executed exactly at the same time?

Let's say I have this code:

function fn(n)
{
  return function()
  {
    for(var k = 0; k <= 1000; ++k) {
      fs.writeSync(process.stdout.fd, n+"\n");
    }
  }
}

setTimeout(fn(1), 100);
setTimeout(fn(2), 100);

Is it possible that 1 and 2 will be printed to stdout interchangeably (e.g. 12121212121...)?

I've tested this and they did NOT apper interchangeably, i.e. 1111111...222222222..., but few tests are far from proof and I'm worried that something like 111111211111...2222222... could happen.

In other words: when I register some callbacks and event handlers in Node can two callbacks be executed exactly at the same time?

(I know this could be possible with launching two processes, but then we would have two stdout and the above code would be splitted into separate files, etc.)

Another question: Forgetting the Node and speaking generally: in any language on single process is it possible for two functions to be executed at exactly the same time (i.e. in the same manner as above)?