Return value for setTimeout function inside a for loop

Question

Hi all when i am executing this piece of code i am getting 40 in my console log can some one plese explain me why

for (var i = 0; i < 10; i++) {
    setTimeout(function () {
        console.log(i);
    }, 300000)
};

possible duplicate of [How to return the response from an asynchronous call?](http://stackoverflow.com/questions/14220321/how-to-return-the-response-from-an-asynchronous-call) — Tushar, Jun 18 '15 at 11:06

score 2 · Accepted Answer · 2015-06-18T11:39:57.130

What you are getting on the console is the id returned by setTimeout(). If you run that code again you might get different value. We cannot predict this id, it is random.

If you want to print the values from 0-9 using setTimeout(), you need to take care of scope.

Using bind():

console.log('before loop');
for (var i = 0; i < 10; i++) {
  setTimeout(function() {
    console.log(this.i);
  }.bind({
    i: i
  }), 1000)
}
console.log('after loop');

Using closures:

console.log('before loop');
for (var i = 0; i < 10; i++) {
  (function(i) {
    setTimeout(function() {
      console.log(i); //<-- parameter i
    }, 1000);
  })(i); //<-- i from loop scope
}
console.log('after loop');

Print in increasing order of timeout.

console.log('before loop');
for (var i = 0; i < 10; i++) {
  setTimeout(function() {
    console.log(this.i);
  }.bind({
    i: i
  }), 100 * i); //<-- note `* i`
}
console.log('after loop');

Thanks Man , this Id can we predict this or rendom . because when i am running my code again and again i am getting values as 40 50 60 .... — Avee, Jun 18 '15 at 11:26

score 0 · Answer 2 · answered Jun 18 '15 at 11:17

0

Your code will print 10 after 300.000 milliseconds.

Try setting it to a shorter period and you will see 10 printed.

What you probably see is linenumber in the console.

answered Jun 18 '15 at 11:17

drbeat

13
5

score 0 · Answer 3 · answered Jun 18 '15 at 11:32

when I am executing this piece of code I am getting 40 in my console log

The reason is that setTimeout() moves the function from the execution queue, it will only be invoked after JavaScript has finished with the current execution queue.
Understanding JavaScript Timers

Return value for setTimeout function inside a for loop

3 Answers3