fixes #207: add a counter parameter to Array analogues that have indices

[michaelficarra]

Fixes #207. Adds "counter" parameters to callbacks of methods that have an Array.prototype analogue that passes an index to its callback. Also removes .indexed() now that it's equivalent to .map((a, i) => [i, a]).

Feedback on #207 has been mixed. I am not yet convinced that this is an improvement, but I am also not opposed to this change if that's what the committee decides.

[ljharb]

The PR does what it claims to do, but I'm even less enthusiastic about it than "unconvinced".

[rbuckton]

I'm very much in favor of this as it reduces the complexity of refactoring something like array.map((item, index) => ...) to iter.map((item, index) => ...), or array.map(existingMapFn) to iter.map(existingMapFn).

[michaelficarra]

I am currently leaning toward merging this. If I don't receive any further feedback soon, we will accept this change.

[zloirock]

It looks like the feedback from #207 is rather against this.

BTW I don't understand why it also removes .indexed() method. Iterators and indexes can be used not only in affected helpers. How do you propose to replace something like this?

for (let [counter, value] of customGenerator().indexed()) { /* some complex logic */ }

[bakkot]

It looks like the feedback from https://github.com/tc39/proposal-iterator-helpers/issues/207 is rather against this.

I see three people who have expressed opposition (you, @ljharb, and @bergus), and three who have expressed support (me, @js-choi, and @rbuckton) (plus two users who just +1'd things, one in each direction). I would not summarize that as "rather against this".

[zloirock]

@bakkot @rbuckton was not in #207 - so #207 is rather against this. Anyway, 50 / 50 is not a reason to merge it.

I'm against indexes param, but not strongly against - it's inconsistency, but useful in some cases. However, I'm strongly against removing the .indexed() helper.

[michaelficarra]

@zloirock This change was discussed during 2 plenary sessions (July and September) and each time it received weak mixed feedback from delegates.

[luncheon]

for (let [value, index] of iter.map(Array)) {
  /* some complex logic */
}