setTimeout(function() {
  alert('World');
}, 0);

alert('Hello');

先hello ,后 world

This can be useful in cases where you want to set a block of code to run as soon as all of the main thread has finished running — put it on the async event loop, so it will run straight afterwards.

clearTimeout() and clearInterval() both use the same list of entries to clear from. Interestingly enough, this means that you can use either method to clear a setTimeout() or setInterval().