Why doesn't Array.from() pass the array to the mapFn?

the kojoman kojoman at gmail.com
Wed May 3 22:12:14 UTC 2017

Thanks Jordan, filter was, of course, what I was looking for. Just got
carried away, when I saw it had a mapFn as an option and thought I could
use that somehow to cut a corner.
By the way, and kind of off topic, why is mutating a list mid-iteration bad
news? I'm just curious, and obviously not a computer engineer.

ons 3 maj 2017 kl 23:37 skrev Jordan Harband <ljharb at gmail.com>:

> Good point :-) i guess as the destination index it makes sense, altho i've
> always thought of it as the source index.
> On Wed, May 3, 2017 at 12:58 PM, T.J. Crowder <
> tj.crowder at farsightsoftware.com> wrote:
>> On Wed, May 3, 2017 at 7:35 PM, Jordan Harband <ljharb at gmail.com> wrote:
>>> (an index in Array.from wouldn't make sense, because Array.from takes an
>>> iterable *or* an arraylike - and only an arraylike would be guaranteed to
>>> have an index, or even a "list" at all)
>> And yet, [it provides one](https://tc39.github.io/ecma262/#sec-array.from).
>> It's the index that will be used to set the array entry from the result.
>> It's only the third argument (the source object) that `Array.from` doesn't
>> include.
>> -- T.J. Crowder
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