Le 29/12/2013 00:11, Rick Waldron a écrit :
On Sat, Dec 28, 2013 at 5:44 PM, Domenic Denicola
<dome...@domenicdenicola.com <mailto:dome...@domenicdenicola.com>> wrote:
I believe that Array.from's only purpose is to provide guidance
for polyfills for people to use in ES3/ES5 code; nobody writing
ES6 would ever use it.
Ignoring any of the previous benefits I've discussed, it seems you're
forgetting about the map function feature of Array.from?
Ok, so to re-focus for those following at home, there are 3 cases to
consider for authors:
1) code only aiming at ES3/5
2) code aiming at both ES3/5 and ES6 environments
3) code only aiming at ES6 envs.
For 1), let's all keep doing what we've been doing. In ES3/5, there is
not really a notion of iterable protocol as it's not used by the
language as it is in ES6.
For 3), from an iterable to an array, it takes ``[...iterable]`` IIUC,
no need for Array.from at all.
2) is the subtle case. There is only one code base. Because it needs to
work in ES3/5, it can't use @@iterable (like jQuery as Rick stated).
However, ES6 code may want to iterate over the arraylikes generated by
the library with for-of and spread. This is where Array.from comes handy
if it works both for @@iterables and arraylikes.
But an Array._from library could work equally well for this purpose. No
need for the built-in Array.from to handle arraylikes.
Dominic Denicola:
I also forgot about how it would be useful for subclasses, e.g.
Elements.from(nodeList), since subclasses don't have their own
dedicated spread syntax. Withdrawn in full.
Oh... super true. Array.from or perhaps less confusingly "just-from"
enables to convert any iterable to another iterable (assuming proper
@@create setup). But that's an ES6-only use case and is unrelated to the
arraylike handling I think.
Side note: it's somewhat ironic that Array carries 'from' given it's the
only "class" that doesn't need it per case study for 3) above :-)
David
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