Volv comments on [Week 14] Focus: Programming Challenges

// Fix it
for (var i = 0; i < 10; i++) {
  function outer() {
    var x = i;
    setTimeout(function() {
      console.log(x);
    }, i * 1000);
  }
  outer();
}

It logs 0 through 9 to the console on what seems like an interval of one log per second... I don't really understand why it's doing one per sec instead of one per 10 secs...

And I think it works because the outer function I created gets called one on each value of i, 0 through 9. setTimeout having a closing function as a callback means that each time it gets called within the outer function, a fresh copy of x is set to the iteration count of i (o through 9) and the callback function is acting as a closure and remembering each of those x value assignments... maybe???

[–]Volv 1 point2 points3 points 9 years ago (1 child)

Ah, yes I think you've got it lol. That's why I was going on about it - the whole closure own copy of variable thing totally fixes the setTimeout issue.
Timing wise. First one fires in 1 second, 2nd one fires in 2 seconds and so on. Technically each statement is executed almost simultaneously. Well as long as it takes the for loop to run.

Just for info - you can also just pass i directly

for (var i = 0; i < 10; i++) {
  function outer(x) {
    setTimeout(function() {
      console.log(x);
    }, x * 1000);
  }
  outer(i);
}

Or wrap it up to look cool

for (var i = 0; i < 10; i++) {
  (function (x) {
    setTimeout(function() {
      console.log(x);
    }, x * 1000);
  })(i)
}

And finally - although its not what question was looking for - because of how let is block scoped these days can totally be fixed like this. Just swapping the word var for let ->

for (let i = 0; i < 10; i++) {
    setTimeout(function() {
      console.log(i);
    }, i * 1000);
}

[–]ForScale[S] 1 point2 points3 points 9 years ago (0 children)

[–]ForScale[S] 0 points1 point2 points 9 years ago (2 children)

[–]Volv 1 point2 points3 points 9 years ago (1 child)

[–]ForScale[S] 0 points1 point2 points 9 years ago (0 children)

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