javascript code raising warning in jshint.com "Functions declared within loops referencing an outer scoped variable may lead to confusing semantics"

Question

The javascript code:

for (j = 0; j < array.length; j ++) {
    if (
        array[j].some(
            function(word) {
                return word.indexOf(array1[i]) > -1;
            }
        )
    ) {
        makeSomething();
    }
}

produces a Functions declared within loops referencing an outer scoped variable may lead to confusing semantics. (array1) warning in jshint.com.

Actually it works.

Is it really problematic?

How should it be written?

You can declare that function outside the for scope and achieve the same result while being more clear — J. Nicastro, Apr 28 '19 at 20:12

score 2 · Answer 1 · answered Apr 28 '19 at 20:12

2

No this is not a problem. The warning is missing the reasoning:

If the callback would be called back asynchronously, then it would be confusing:

   for(i = 0; i < 10; i++) {
      setTimeout(function() {
        console.log(i); // guess what this logs
      });
  }

But you should really always declare variables and always use let or const for that:

  for (let j = 0; j < array.length; j ++) {

that will make the warning go away, and will also fix the example above (and it avoids a probably confusing implicit global).

answered Apr 28 '19 at 20:12

Jonas Wilms

132,000
20
149
151

I cannot understand clearly... in my example shoul I change `for (j = 0` to `for (let j = 0`? – Paolo Benvenuto Apr 28 '19 at 20:20
.... jshint gives a warning with `array1`, how can the `let j` change something? actually, adding the `let`, jshint keeps giving me the same warning – Paolo Benvenuto Apr 28 '19 at 20:40
But now you can ignore it without feeling bad :) – Jonas Wilms Apr 28 '19 at 20:41

score 0 · Answer 2 · answered Apr 28 '19 at 20:15

You can declare that function outside the for scope and achieve the same result while avoiding the warning.

const functionName = function(word) {
    return word.indexOf(array1[i]) > -1;
}

for (let j = 0; j < array.length; j ++) {

    if (array[j].some(functionName)) {
        makeSomething();
    }
}

score -1 · Answer 3 · answered Jan 23 '21 at 19:02

-1

you need just to declare the function outside the for loop , then call it inside the loop as guest

answered Jan 23 '21 at 19:02

madjed-hue

16
3

1

Why not give the code instead of just describing?! – Thodoris Jan 23 '21 at 21:51

javascript code raising warning in jshint.com "Functions declared within loops referencing an outer scoped variable may lead to confusing semantics"

3 Answers3