Function.create

[Xavier MONTILLET]

I don't get the difference between the proto operator and some
setPrototype method that could be added (or the actual __proto__
property)...

On Sat, Sep 24, 2011 at 6:03 PM, David Bruant <david.bruant at labri.fr> wrote:
> Le 24/09/2011 15:33, Jake Verbaten a écrit :
>> There is no standardized way to create a new function with a prototype
>> which is not Function.prototype.
>>
>> I propose Function.create
>>
>>     /*
>>       Creates a new function whose prototype is proto.
>>       The function body is the same as the function fbody.
>>       The hash of propertydescriptors props is passed to
>> defineproperties just like
>>       Object.create does.
>>     */
>>     Function.create = (function() {
>>       var functionBody = function _getFunctionBody(f) {
>>         return f.toString().replace(/.+\{/, "").replace(/\}$/, "");
>>       };
>>       var letters = "abcdefghijklmnopqrstuvwxyz".split("");
>>
>>       return function _create(proto, fbody, props) {
>>         var parameters = letters.slice(0, fbody.length);
>>         parameters.push(functionBody(fbody));
>>         var f = Function.apply(this, parameters);
>>         f.__proto__ = proto;
>>         Object.defineProperties(f, props);
>>         return f;
>>       };
>>     })();
>>
>> This is the same as Object.create except the second parameter is a
>> function.
>>
>> It will create a new function whose function body is the same as the
>> function passed in.
>>
>> I don't believe this is possible to do in ES5 without __proto__
> It is not indeed.
> This topic has been discussed a couple of times here. There is one
> proposal that is more generic than your solution which is the proto
> operator [1].
>
> Basically, to create a function with a chosen prototype, you can do:
> -----
> var f = myProto <| function(a, b){return a+b;}
> Object.getPrototypeOf(f); // myProto
> f(1, 2); // 3
> -----
>
> I'm a big fan of the proto operator proposal, however, as raised
> previously this operator relies on the object being created to have an
> intialisation syntax. This prevents, for instance, Date objects to have
> a custom prototype with this method. I am not very familiar with it yet,
> but I think that if they ever came to life, ParallelArrays [2] would
> suffer from the same problem.
> By the way, could someone add this concern as a note ("open issue" or
> "limitation" or something like this) in the proto operator page, please?
>
> One even more generic way which would work even for objects that have no
> initialization syntax would to standardize one of [3] or [4]. Is there a
> wiki page mentionning these two functions somewhere? If not, may it be
> added and linked in some way to the proto operator?
>
> David
>
> [1] http://wiki.ecmascript.org/doku.php?id=harmony:proto_operator
> [2]
> https://github.com/RiverTrail/RiverTrail/blob/15ae7f6f77d9d2842d9d75458017efd9fe0fbee7/jslib/ParallelArray.js#L29
> [3] https://mail.mozilla.org/pipermail/es-discuss/2011-March/013141.html
> [4] https://mail.mozilla.org/pipermail/es-discuss/2011-March/013154.html
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