Question

Possible Duplicate:
Javascript closure inside loops – simple practical example

Seen many posts talking about setTimeout and closures but I’m still not able to pass in a simple for loop counter.

for (i = 0; i < 5; i++) {
  setTimeout(function () {
    console.log(i);
  }, Math.floor(Math.random() * 1000));
}

Gives

5
5
5
5
5

Would like to have

0
1
2
3
4

What’s wrong ?
Please don’t flame, I thought I have understood the setTimeout() tale but apparently not.

Answer 1

You can use a closure to keep a reference to the current value of i within the loop:

for (i = 0; i < 5; i++) {
    (function(i) {
        setTimeout(function () {
            console.log(i);
        }, Math.floor(Math.random() * 1000));
    })(i); //Pass current value into self-executing anonymous function
}​

However, this is unlikely to print the numbers in order since you use a random timeout (you could use i * 1000 instead to make the numbers print in ascending order, one second apart).

Here’s a working example.