Rick Waldron waldron.rick at
Wed May 14 08:00:50 PDT 2014

On Wed, May 14, 2014 at 5:37 AM, Till Schneidereit <
till at> wrote:

> On Wed, May 14, 2014 at 8:48 AM, Mathias Bynens <mathiasb at>wrote:
>> Previous discussion on this topic:
>> We should look at how existing utility libraries handle this behavior and
>> base any proposals on that IMHO. Underscore and Lo-Dash have [`_.first`](
>> and [`_.last`](,
>> which both take an optional `callback` parameter, in which case all the
>> first/last `n` elements for which `callback` returns a truthy value are
>> returned. This seems like a sensible thing to add to the proposal.
> While I think having .last would be nice, I don't think it's worth the
> considerable backwards-compatibility issues. We had to temporarily back out
> Array#values from SpiderMonkey until we implement @@unscopable
> semantics[1], because we ran into serious real-world breakage. I'm pretty
> sure that "last" would break a lot more code, as it's even easier to think
> up scenarios where that'd be used as a property name on an array used in
> application logic.
> At the very least, I think having Array#last be a getter is entirely
> untenable: a method would at least just be overwritten in most cases,
> whereas a read-only accessor would just (silently, in non-strict code)
> fail. A read-write accessor would probably be even worse: it'd silently (in
> all code) do something entirely different than it did before.
> I do, however, like Axel's proposal[2] of adding .get() and .set() to
> Array.prototype, and think that that'd be way less of a compatibility issue.
> [1]:
> [2]:

I forgot about this, thanks for posting. I like get() much better as it can
be a "first" or a "last"  (or any in between) with less surface impact.

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