On Fri, Mar 8, 2013 at 6:31 PM, Andrea Giammarchi <
[email protected]> wrote:
> also .. how that happened that Array.from is basically the equivalent of
>
> Array.from = Function.call.bind(Array.prototype.map); ?
>
> Wasn't the initial reason to Array.from avoid the repeated all over
> everywhere [].slice.call(arguments) where a signature slice-alike would be
> more suitable so instead of Array.from(arguments).slice(1), as example, one
> would Array.from(arguments, 1) ?
>
The addition of a "map callback" is to give subclasses, that inherit
Array.from() a way of creating new "collection likes", of their _own_ type.
You wouldn't want subclasses to return the parent classes type:
class Vector extends Array {}
Vector.from( ... ) // I want a new Vector, not an Array.
The example I gave during Allen's presentation:
var nodelist = NodeList.from(["div"], nodeName =>
document.createElement(nodeName) );
Full discussion:
https://github.com/rwldrn/tc39-notes/blob/master/es6/2013-01/jan-29.md#48-refactored-new-operator-and-the-create-method(search
for "Conclusion/Resolution, Bullet 2")
The proposed and accepted solution:
https://github.com/rwldrn/tc39-notes/blob/master/es6/2013-01/jan-30.md#revising-the-array-subclassing-kind-issue
Rick
>
> Thanks again :-)
>
>
>
> On Fri, Mar 8, 2013 at 3:26 PM, Andrea Giammarchi <
> [email protected]> wrote:
>
>> am I understanding mixin correctly?
>>
>> 'mixin' in Object || (Object.mixin = function mixin(
>> target, source
>> ) {
>> for(var
>> keys = Object.getOwnPropertyNames(source),
>> i = keys.length; i--; Object.defineProperty(
>> target,
>> keys[i],
>> Object.getOwnPropertyDescriptor(
>> source,
>> keys[i]
>> )
>> )
>> );
>> return target;
>> });
>>
>> thanks
>>
>>
>> On Fri, Mar 8, 2013 at 2:35 PM, Allen Wirfs-Brock
>> <[email protected]>wrote:
>>
>>> The March 8, 2013 Rev 14 draft is now available at the usual place:
>>> http://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts
>>>
>>> Changes include:
>>>
>>> - Class bodies are now always string
>>> - *static* methods may now be defined in *ClassBody*
>>> - Updated comprehension syntax to use left-to-right order
>>> - Eliminated *is* and *isnt* operators
>>> - added grammar productions to allow unqualified super to be used
>>> after new operator
>>> - expression to the right of *of* in *for-of* now restricted to
>>> being *AssignmentExpression*
>>> - Almost all Chapter 15 constructors are now specified to have an
>>> @@create methid and are initialized in a manner that supports
>>> subclassing.
>>> (still need to work on Function)
>>> - Added Object.getOwnPropertyKeys function
>>> - Added Object.is function
>>> - Tentatively added Object.mixin function
>>> - Array.from now takes an optional map function
>>> - Added String.prototype.normalize method
>>> - All String.prototype methods that accept RegExp arguments will
>>> now work with subclasses of RegExp
>>> - Renamed Number.prototype.toInt to Number.prototype.toInteger
>>> - RegExp global, ignoreCase, multiline, source, sticky are now
>>> prototype accessor properties rather than instance own data properties.
>>> This is needed to support adding web compatible compile method.
>>> - Added new RegExp.prototype methods that allow string methods to
>>> work with RegExp subclasses: match, replace, search, split, @@isRegExp
>>> - Map and Set constructors now accept a =n optional comparator
>>> parameter. Only value currently allowed is “is”
>>> - ArrayBuffer and *Typed*Array object length no long restricted to 2
>>> 32 limit
>>> - Eliminated all remaining references to [[Class]] and
>>> [[NativeBrand]] (except for in some DataView code that needs rewritting
>>> anyway)
>>> - Added SameValueZero abstraction operation that considers -0 and
>>> +0 to be the same value.
>>> - Rename [[GetP]] to [[Get]] and [[SetP]] to [[Set]]
>>> - Specified that unless otherwise indicated, internal data
>>> properties are created when an object is allocated. Internal data
>>> properties are now explicitly listed in ObjectCreate abstract operation
>>> calls.
>>> - internally consolidated [[IsExtensible]]/[[IsSealed]/[[IsFrozen]]
>>> and [[PreventExtensions]]/[[Seal]]/[[Freeze]] into two MOP operations
>>> [[HasIntegrity]] and [[SetIntegrity]]. However, no public APIs (Proxy
>>> traps
>>> and Reflect functions) changed.
>>> - Numerous editorial and technical corrections, clarifications, and
>>> bug fixes
>>>
>>>
>>>
>>> _______________________________________________
>>> es-discuss mailing list
>>> [email protected]
>>> https://mail.mozilla.org/listinfo/es-discuss
>>>
>>>
>>
>
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