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, Mar 17 '21 at 11:12
Why is a nested loop considered a "bad code smell"? Or do you mean that the loops share variables? — evolutionxbox, Mar 17 '21 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, Mar 17 '21 at 11:13
There is a lint rule for this https://eslint.org/docs/rules/no-shadow, I assume it would detect this case — evolutionxbox, Mar 17 '21 at 11:15
@T.J.Crowder it was your use of shadow that reminded me of its existence — evolutionxbox, Mar 17 '21 at 11:20
@T.J.Crowder hahaha that's true:-), thanks for reminding, corrected now. — ist, Mar 18 '21 at 05:19

score 6 · Accepted Answer · answered Mar 17 '21 at 11:16

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);
    }
}

score -1 · Answer 2 · answered Mar 17 '21 at 11:11

-1

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

answered Mar 17 '21 at 11:11

user7090959

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

2 Answers2