On Tue, Oct 7, 2014 at 11:46 AM, Domenic Denicola < [email protected]> wrote:
> From: es-discuss [mailto:[email protected]] On Behalf Of > Dmitry Soshnikov > > > Am I still missing something? > > Yes. > > ```js > var uint16s = new Uint16Array([258]); > var uint8s = Uint8Array.from(uint16s, x => x / 2); > console.log(uint8s); // [129] > ``` > > ```js > var uint16s = new Uint16Array([258]); > var uint8s = Uint8Array.from(uint16s).map(x => x / 2); > console.log(uint8s); // [1] > ``` > > Moreover, these two examples are semantically completely different. They confuse and substitute the pre- and post- mapping. Clearly, it should be pre-mapping here, and the second example is not even correct from this perspective. And exactly manually pre-map it, is seems better, because that `mapfn` on the API level can simply be confusing: what does it do -- maps pre- or post? And as mentioned above, after the correct list is constructed (with possible pre-mapping), developers can also post-map it calling the `Array.prototype.map` that still preserves the kind of the collection. So I'd say, we should exclude the `mapfn` from `Array.from` in order to keep the implementation (including polyfills) simpler and responsible for only one things -- building a <ArrayKind> collection from another collection or an iterable, consuming _correct_ data. Dmitry
_______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
