Le 28/12/2013 15:25, Brendan Eich a écrit :
This seems overcomplicated. Isn't the likelier code something like
Array.from || (Array.from = function(b) { var a=[]; for (var i=0;
i<b.length; i++) a.push(b[i]); return a; });
Isn't the whole point to impute arraylikeness to the parameter?
In any case the important point is that it's possible to implement in an
ES5 env whatever behavior is expected from Array.from in an ES6 env.
Granted, it's not super elegant solution, but it does work. The
overhead becomes significant only in the degenerate cases where
dozens of libraries override Array.from.
David, I took your side in the TC39 meeting, as the meeting notes
disclosed. Rick prevailed (I think, my memory is hazy).
It's what I read from the notes too, but I feel something may have been
overlooked.
You want the polyfillers to pay the price, while Rick proposes that
ES6's built-in absorb arraylike fallback handling.
The difference is not in the polyfill (old browser) case, but in the
present and future (ES6 and above) cases: some objects will remain
arraylike yet lack @@iterator.
In ES6 and above, why would one create such an object? What's a good use
case?
My understanding of the current consensus is that an arraylike without
@@iterator wouldn't work for for-of loops nor spread. Why not just
create an array? jQuery and Zepto want to subclass Array (one creates
arraylike, the other does subclass setting __proto__). It wasn't
possible in ES5, but is in ES6 with classes (and the super+@@create
infrastructure).
I feel that all the cases that justified arraylikes in the past have
much better alternatives in ES6.
My little experience building a Firefox addon even suggests that sets
replace arrays in most situations as most of what I do with arrays is
.push, for-of and .map/filter/reduce (by the way, Set.prototype needs
these too, but another topic for another time).
Why shouldn't Array.from help them out?
If these objects have a good reason to exist in an ES6 and above world,
I agree, that's a good point. But is there a use case justifying their
existence?
David
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