On Wed, May 14, 2014 at 8:48 AM, Mathias Bynens <[email protected]> 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
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