B.3.1 The __proto__ pseudo property

Andrea Giammarchi andrea.giammarchi at gmail.com
Tue May 21 09:44:24 PDT 2013


for always work I meant as long as the object is not sealed/frozen as
discussed a while ago


On Tue, May 21, 2013 at 9:43 AM, Andrea Giammarchi <
andrea.giammarchi at gmail.com> wrote:

> On Tue, May 21, 2013 at 12:56 AM, Brendan Eich <brendan at mozilla.com>wrote:
>
>> Andrea Giammarchi wrote:
>>
>>> can I also suggest to analyze, if there's still any doubt left on a
>>> method VS a property yet, this piece of code if not highlighted before?
>>>
>>
>> I do not understand what you mean here.
>>
>>
> I mean that JSON, as part of the specs, needs to consider that "magic"
> property case, resulting into an `instanceof Object`, with an enumerable
> property that will show up in a `for/in` loop but it's not able to mutate
> the object.
>
> ```
> var obj = JSON.parse('{"__proto__":[]}');
> alert(obj instanceof Array); // false
> alert(obj["__proto__"] instanceof Array); // true
> obj["__proto__"] = obj["__proto__"];
> // or
> for (var key in obj) {
>   obj[key] = obj[key];
>   // could be a generic
>   // clone operation
> }
> alert(obj instanceof Array); // false
> alert(obj instanceof Object); // true
> ```
>
> Above kind of object is "not perfectly described in current specs" and is
> different from any other where the `__proto__` is the inherited and not own
> property.
>
> This is what developers should be aware of, that `__proto__` might not be
> what they think is while `Object.setPrototypeOf(obj, proto):obj` will
> always work as expected, as well as `Object.getPrototypeOf(obj):proto`
>
> All I am saying is that I understood reasons `__proto__` is there but I
> hope there won't be any step backward about `Object.setPrototypeOf`
>
> All the best and looking forward to read the notes.
>
>
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