closures in for loops in javascript

Question

I am trying to reproduce the example with the IIEF here:

Understand JavaScript Closures With Ease

EDIT

It's under 3. Closures Gone Awry

This is my code:

var myArray = ["a", "b", "c"];

function doSomething(someArray) {
  var counter = 10;
  for (var i = 0; i < someArray.length; i++) {
    someArray[i] = function(inner_i) {
      return function() {
        return counter += inner_i;
      }();
    }(i);
  }
  return someArray;
}

var newArray = doSomething(myArray);
console.log(newArray[0]);
console.log(newArray[1]);
console.log(newArray[2]);

The output is

10
11
13

instead of

10
11
12

What am I doing differently?

The inner_i is 2 in your third loop which means: counter+=inner_i equals 11+2=13 just return counter + inner_i — KRONWALLED
– KRONWALLED, Commented Jun 10, 2016 at 10:53
"What am I doing differently?" How are we to know? You haven't shown the code you're comparing your code to. — T.J. Crowder
– T.J. Crowder, Commented Jun 10, 2016 at 10:57

T.J. Crowder · Accepted Answer · 2016-06-10 10:57:46Z

3

There is nothing wrong in the result, because you are updating the value of counter in each iteration. Instead just return the sum of counter and i.

var myArray = ["a", "b", "c"];

function doSomething(someArray) {
  var counter = 10;
  for (var i = 0; i < someArray.length; i++) {

    someArray[i] = function(inner_i) {
      return function() {
        return counter + inner_i;
      }();
    }(i);
  }

  return someArray;
}

var newArray = doSomething(myArray);
console.log(newArray[0]);
console.log(newArray[1]);
console.log(newArray[2]);

edited Jun 10, 2016 at 10:57

T.J. Crowder

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answered Jun 10, 2016 at 10:55

Pranav C Balan

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1 Comment

NotSmartButLucky Over a year ago

Thanks a lot!! Totally didn't see that!

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