Allow variable declarations with guard-for-in

What rule do you want to change? guard-for-in

Does this change cause the rule to produce more or fewer warnings? Fewer.

How will the change be implemented? (New option, new default behavior, etc.)? New default behavior.

Please provide some example code that this change will affect:

for (key in foo) {
    const val = checkSomething(key)
    if (val > 0) {
        doSomething(key, val);
    }
}

What does the rule currently do for this code? Warns.

What will the rule do after it’s changed? Not warn.

---

The point is that the condition(s) that you check to filter properties may involve values that are also needed inside the loop body. It would be good to allow this without having to disable or work around the warning. I.e. allow let and const statements before the if.

[not-an-aardvark]

Thanks for the suggestion.

I’m not sure about this change; I think the point of the guard-for-in rule is to enforce the following pattern:

for (key in foo) {
  // Only do things if `key` is an own property of `foo`, rather than an inherited property.
  if (Object.prototype.hasOwnProperty.call(foo, key)) {
    // do logic, including const and let declarations, in this `if` statement
  }
}

[kaicataldo]

Feel free to make a new issue with a proposal!