Array.prototype.last()

Andrea Giammarchi andrea.giammarchi at gmail.com
Wed May 14 10:10:44 PDT 2014


I like we keep adding `get` and `set` here and there but I hope we are not
forgetting to fix descriptors inheritance problem where any `get` or `set`
can compromise `Object.defineProperty` operations (just a gently reminder
that `get` and `set` if inherited can cause many troubles in ES5 like
operations)

Best Regards


On Wed, May 14, 2014 at 8:00 AM, Rick Waldron <waldron.rick at gmail.com>wrote:

>
>
>
> On Wed, May 14, 2014 at 5:37 AM, Till Schneidereit <
> till at tillschneidereit.net> wrote:
>
>> On Wed, May 14, 2014 at 8:48 AM, Mathias Bynens <mathiasb at opera.com>wrote:
>>
>>> Previous discussion on this topic:
>>> http://esdiscuss.org/topic/array-prototype-last
>>>
>>> We should look at how existing utility libraries handle this behavior
>>> and base any proposals on that IMHO. Underscore and Lo-Dash have
>>> [`_.first`](http://lodash.com/docs#first) and [`_.last`](
>>> http://lodash.com/docs#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]:
>> https://mail.mozilla.org/pipermail/es-discuss/2013-July/thread.html#32185
>> [2]: http://esdiscuss.org/topic/array-prototype-last#content-5
>>
>
> 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.
>
> Rick
>
>
>
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