How to detect nested loop with same index in JavaScript/TypeScript

Question

I am trying to detect nested loop with the same index which looks like this:

for(let i = 0; i < 10; i++) {
    for(let i = 0; i < 10; i++) {
    }
}

I have searched Eslint rules but haven't found any solution so far. Is there a way to detect this bad code smell? Thanks a lot.

I can't help trying to be humorous and pointing out that in that particular case, it won't matter, since the inner loop body will never run. ;-) (i = 0; i < 0...) ;-) — T.J. Crowder
– T.J. Crowder, Commented Mar 17, 2021 at 11:12
Why is a nested loop considered a "bad code smell"? Or do you mean that the loops share variables? — evolutionxbox
– evolutionxbox, Commented Mar 17, 2021 at 11:12
@evolutionxbox - Not nested loops per se, nested loops with the same index variable. The inner one will shadow the outer one. I could see the argument that this is asking for trouble. :-) — T.J. Crowder
– T.J. Crowder, Commented Mar 17, 2021 at 11:13
There is a lint rule for this eslint.org/docs/rules/no-shadow, I assume it would detect this case — evolutionxbox
– evolutionxbox, Commented Mar 17, 2021 at 11:15
@T.J.Crowder it was your use of shadow that reminded me of its existence — evolutionxbox
– evolutionxbox, Commented Mar 17, 2021 at 11:20

T.J. Crowder · Accepted Answer · 2021-03-17 11:16:58Z

6

ESLint has the no-shadow rule that would flag that up, as well as other places where you've shadowed an outer scope variable with an inner scope one. For example:

{
    "no-shadow": ["error", { "builtinGlobals": false, "hoist": "functions", "allow": [] }]
}

Demo on the ESLint site:

for(let i = 0; i < 10; i++) {
    for(let i = 0; i < 10; i++) {
//          ^−−−−− 'i' is already declared in the upper scope on line 1 column 9.
        console.log(i);
    }
}

answered Mar 17, 2021 at 11:16

T.J. Crowder

1.1m201 gold badges2k silver badges2k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

user7090959 · Accepted Answer · 2021-03-17 11:11:47Z

-1

You can't do it, since it's pure logic

answered Mar 17, 2021 at 11:11

user7090959

14 bronze badges

Collectives™ on Stack Overflow

How to detect nested loop with same index in JavaScript/TypeScript

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related