On Mon, Oct 6, 2014 at 8:19 PM, Rick Waldron <waldron.r...@gmail.com> wrote:
> > > On Mon, Oct 6, 2014 at 10:59 PM, Dmitry Soshnikov < > dmitry.soshni...@gmail.com> wrote: > >> Hi, >> >> We're currently polyfilling `Array.from` in our codebase following the >> latest draft [1]. And I was actually surprised by the `mapfn` being >> involved into the algorithm. >> > > Have you tried es6-shim? > > Yeah, I'm aware of it, though, we have own versions for better performance, since may skip some internal checks, etc. > >> I mean, from the performance perspective it's probably .. ok-ish.. but >> from the API design perspective it feels like combining the actual >> transformation of an iterable (or of an array-like) with the mapping, is >> the "too much of responsibility" anti-pattern. Why not filter then as well? >> (or, as one of the comments on a diff review: "I'm actually disappointed >> it won't do my laundry as well :P"). >> >> It probably should be just: >> >> ``` >> Array.from(...).map(mapfn); >> ``` >> >> Unless I'm missing something, and there was a special reason to include >> the mapping. >> > > Yes: > https://github.com/rwaldron/tc39-notes/blob/c61f48cea5f2339a1ec65ca89827c8cff170779b/es6/2013-01/jan-30.md#revising-the-array-subclassing-kind-issue > Any subclass of array will want to produce a list of its own "kind", but > .map returns an Array. This thread is also a dup of: > https://mail.mozilla.org/pipermail/es-discuss/2013-June/031500.html > > I see. OK, thanks Rick, will re-read. Dmitry
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