My main concern was about non `Array` objects such instances of `Arguments` or `NodeList` or others Array_ish_ instances where to work with `.slice()` all we need is a `length` property.
If these will return not as `instanceof` current `Array` realm most of the code will be broken. If `.slice()` will be that smart as I expect, I wonder why nobody is mentioning `.concat()` as able to concatenate every Array_ish_ and produce an `instanceof` the original object constructor that invoked that concat call. `ArrayIsh.prototype.concat([]) instanceof ArrayIsh` Last doubt would be about `Array.isArray` and the inability to distinguish, if not via `Object#toString` or `instanceof` between two different `ArrayIsh` objects ... so that `instanceof` will be not usable for `ArrayIsh` and at the same time the best solution to understand what kind of `ArrayIsh` it is so that extra, enriched, methods can be used. Thoughts? On Tue, Sep 10, 2013 at 12:25 PM, Allen Wirfs-Brock <[email protected]>wrote: > > On Sep 10, 2013, at 11:12 AM, Andrea Giammarchi wrote: > > > As short answer, let me reformulate: > > AFAIK 99% of libraries out there believe that slice.call will return an > Array, no matter which realm. In ES6 I see there's too much magic involved > because of subclassing possibility. > > Presumably this is a 100% reasonable expectation today, because that's > that the ES<=5.1 specs say. However, often do they depend upon the value > being a direct instance of Array as opposed to being an instance of a > subclass of an array, assuming that the subclass how all the observable > characteristics of an Array instances including answering true to > Array.isArray and maintaining the Array invariant. > > In other words, those libraries have never encountered a true subclass of > Array. When they do, is anything bad going to happen if the result object > is also a subclass of Array? > > BTW, I think it is useful to distinguish this use case from applying slice > to non Array.isArray objects or using slice as a strange way to create a > new Array instance. > > Allen > > > > >
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