Settimeout不会立即返回

Question

I was practicing with callback functions and this question is one I can't seem to figure out.

function foo () {    
  var data = 10;    
  bar(function (players) {
    data = players;
  });    
  return data;
}

function bar (callback) {
  setTimeout(callback, 0);
}

var result = foo();

I expected result to be undefined since data = players and there is nothing passed in as players. Since the setTimeout function uses 0 as the delay, shouldn't it run first, and then return data? I looked at the MDN page and there seems to be information on throttling for nested timeouts to >=4ms . Does this also apply in this case?

Answer 1

Since the setTimeout function uses 0 as the delay, shouldn't it run first, and then return data?

No, even with a delay of 0 , the callback passed to setTimeout is scheduled to run in the next tick of the event loop .

In other words, the callback is guaranteed to be executed after the current execution ran to completion.