For loop breaks an unrelated array

Question

Hey so I am using puppeteer and when I run this code:

console.log(dealsId[i]);

for (var i = 0; i < sizes.length; i++) {
    var refIdClasses = await sizes[i].$eval('input', a => a.getAttribute('class'));
    if (refIdClasses != 'disabled') {
        var refId = await sizes[i].$eval('input', a => a.getAttribute('value'));
        var size = await sizes[i].$eval('input', a => a.getAttribute('data-size'));
        refIds.push({ size: size, refId: refId });
    }
}
console.log(dealsId[i]);

The Deals Id works before the for loop and after the loop it says undefined and I am so confused on why.

ouflak · Accepted Answer · 2021-11-05 13:21:29Z

3

Var i is globally-scoped, so by using var i=0 you are definitely creating scope conflict. Use let or another variable name instead.

edited Nov 5, 2021 at 13:21

ouflak

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answered Nov 5, 2021 at 10:31

newt

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Comments

Gaëtan Boyals · Accepted Answer · 2021-11-05 10:29:49Z

1

That's the problem with vars. You can declare and re-declare them in the same scope without warning.

I assume you declared a var i in the code before what you showed, but you re-declare it in the for loop. i < sizes.length being the condition to break the loop, the loop break and i is now out-of-bounds of your array, hence the undefined (if dealsId has a size that's inferior to sizes array).

It isn't "unrelated" since you used the same variable to loop through 2 different arrays. Since we don't know if the two arrays have the exact same size, we can't pinpoint with 100% accuracy what's going on, but I'll go with that.

answered Nov 5, 2021 at 10:29

Gaëtan Boyals

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Comments

Nabeel Khan · Accepted Answer · 2021-11-06 22:16:12Z

0

This is because your for loop is also using i to iterate, possibly conflicting with the i in dealsId[i].

Possible solution might be to change the variable in for loop from i to j.

The code becomes:

console.log(dealsId[i]);

for (var j = 0; j < sizes.length; j++) {
    var refIdClasses = await sizes[j].$eval('input', a => a.getAttribute('class'));
    if (refIdClasses != 'disabled') {
        var refId = await sizes[j].$eval('input', a => a.getAttribute('value'));
        var size = await sizes[j].$eval('input', a => a.getAttribute('data-size'));
        refIds.push({ size: size, refId: refId });
    }
}
console.log(dealsId[i]);

edited Nov 6, 2021 at 22:16

answered Nov 5, 2021 at 10:31

Nabeel Khan

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3 Comments

Casimir et Hippolyte Over a year ago

Yes, it's a possible solution, but a good solution is to use a for...of loop, that doesn't need a useless index variable at all.

Casimir et Hippolyte Over a year ago

Probably sizes[i] needs to be sizes[j].

Nabeel Khan Over a year ago

@CasimiretHippolyte you can revert the downvote :) i have edited the code for it

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