On Wed, Oct 8, 2014 at 2:42 PM, Dmitry Soshnikov <[email protected] > wrote:
> On Tue, Oct 7, 2014 at 4:08 PM, Claude Pache <[email protected]> > wrote: > > >> Le 7 oct. 2014 à 23:43, Dmitry Soshnikov <[email protected]> a >> écrit : >> >> On Tue, Oct 7, 2014 at 2:35 PM, Tab Atkins Jr. <[email protected]> >> wrote: >> >>> On Tue, Oct 7, 2014 at 2:26 PM, Dmitry Soshnikov >>> <[email protected]> wrote: >>> > I see. Actually it doesn't work, your're correct, since >>> > `Array.prototype.map` does preserve the kind (at least in the latest >>> draft). >>> >>> Hmm, per Rick's earlier email and >>> < >>> https://github.com/rwaldron/tc39-notes/blob/c61f48cea5f2339a1ec65ca89827c8cff170779b/es6/2013-01/jan-30.md#revising-the-array-subclassing-kind-issue >>> >, >>> Array#map (used by a subclass) doesn't preserve the subclass's type; >>> it always returns an Array. >>> >>> > And the `UInt32Array.from(...)` would be consuming a nodeList, not an >>> array. >>> > Will the `nodeList.map(node => parseInt(node.value, 10));` by itself >>> > actually work then? >>> >>> If .map() is inherited from Array, and thus not type-preserving, yes, >>> it'll work. >>> >>> >> Yes, it is preserving (probably was changed since that previous >> discussion), see (9) in >> http://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.prototype.map. >> Will a simple map to `node.value` on a `NodeList` work with the preserving >> `Array#map`? >> >> >> So, a `SortOfArray.from` (with a mapping) is finally less confusing than >> a `SortOfArray#map`, for you don't have to look at the doc in order to >> determine the type of the result... :-p >> >> > Also related, and came on Twitter just not: > https://twitter.com/DmitrySoshnikov/status/519964146637737986 > > The mapping function from `Array.from` considers holes (from the new TC39 > "policy"), but `Array#map` does not. > > I guess this doc on `Array.from` from MDN [1] should be fixed then: > > > More clearly, Array.from(obj, mapFn, thisArg) is the same as > Array.from(obj).map(mapFn, thisArg), except that it does not create an > intermediate array. > > Since not only they are "the same" (as we confuse/substitute pre- and > post- mapping), but also the mapping function itself behaves differently. > > [1] > https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from > > Never mind, as Rick and Allen clarified, they will produce the same arrays, because of behavior of `Array.from` which as a result already has a hole converted to explicit `undefined` value. Here is an example: http://gyazo.com/4709305f3bde1c8ce0b02d2071a99e7f Dmitry
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