ref(eslint): enable typescript-eslint/no-for-in-array

[TkDodo]

While it’s legal to iterate over an array with for-in, it’s likely not intended (for-in iterates over the properties of an Object) because it will return the index as a string, and has other room for bugs as stated here.

Moving to for-of is a better fix in many places, as it will also rid us of no-null assertions when doing an indexed access.

[TkDodo]

note: I’m pretty sure this can’t have worked before. If we iterate with:

for (const errorKey in Object.keys(errorMessages))

errorKey will be the stringified index of the keys array, so ['0', '1'] etc. Then, going to the actual errorMessages object and deleting something at '0' doesn't do anything unless the key is literally the string '0'.

Maybe the intention was to do:

for (const errorKey in errorMessages)

to iterate over all keys?

@roggenkemper am I missing something here?

[roggenkemper]

good catch! i guess the case that it covered wasn't common enough to come up often.

[JonasBa]

Nice to see this might have also caught a bug in that loop. Approving the PR (provided @roggenkemper confirms this fixes a bug)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Lines      586114   586100      -14     
  Branches    22618    22618              
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- Hits       513417   513403      -14     
  Misses      72278    72278              
  Partials      419      419