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From: kangax on 17 Jan 2010 11:51
On 1/17/10 9:46 AM, Asen Bozhilov wrote:
> kangax wrote:
[...]
>> Also, why only 3 out of 7?
>
> Which others four? I don't find good article about {DontEnum} bug in
> JScript implementation. I know only for that three user defined
> properties in native objects. Can you give link or example?
> Thanks.

Garrett explained it here
<http://dhtmlkitchen.com/learn/js/enumeration/dontenum.jsp#JScriptDontEnumBug>

To quote:

"JScript will skip over any property in any object where there is a
same-named property in the object's prototype chain that has the
DontEnum attribute."

For a list of `Object.prototype` properties see 15.2.4 (ES3F).

--
kangax
From: kangax on 17 Jan 2010 12:03
On 1/17/10 10:02 AM, Thomas 'PointedEars' Lahn wrote:
> kangax wrote:
>
>> Asen Bozhilov wrote:
[...]
>>> },
>>>
>>> addProperties : function(o)
>>> {
>>> for (var i in o)
>>> {
>>> if (o.hasOwnProperty(i))
>>
>> Would be safer to do:
>>
>> if (Object.prototype.hasOwnProperty.call(o, i))
>
> How so? All built-in objects need to implement hasOwnProperty() as they
> have Object.prototype in their prototype chain, and nobody sane would pass
> a host object here.

Think about what happens when `{ hasOwnProperty: null }` is passed to
`addProperties` method.

[...]

--
kangax
From: Thomas 'PointedEars' Lahn on 17 Jan 2010 12:55
kangax wrote:

> Thomas 'PointedEars' Lahn wrote:
>> kangax wrote:
>>> Asen Bozhilov wrote:
> [...]
>>>> },
>>>>
>>>> addProperties : function(o)
>>>> {
>>>> for (var i in o)
>>>> {
>>>> if (o.hasOwnProperty(i))
>>>
>>> Would be safer to do:
>>>
>>> if (Object.prototype.hasOwnProperty.call(o, i))
>>
>> How so? All built-in objects need to implement hasOwnProperty() as they
>> have Object.prototype in their prototype chain, and nobody sane would
>> pass a host object here.
>
> Think about what happens when `{ hasOwnProperty: null }` is passed to
> `addProperties` method.

Nobody sane would create such an object either, or pass a reference to it
to this method.


PointedEars
--
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evangelism: XHTML 1.0 Strict
madness: XHTML 1.1 as application/xhtml+xml
-- Bjoern Hoehrmann
From: Jorge on 17 Jan 2010 13:05
On Jan 17, 6:55 pm, Thomas 'PointedEars' Lahn <PointedE...(a)web.de>
wrote:
> kangax wrote:
>
> > Think about what happens when `{ hasOwnProperty: null }` is passed to
> > `addProperties` method.
>
> Nobody sane would create such an object either, or pass a reference to it
> to this method.

LOL.

Object.prototype.hasOwnProperty.call({ hasOwnProperty: null },
"hasOwnProperty");
--> true

--
Jorge.
From: Thomas 'PointedEars' Lahn on 17 Jan 2010 13:10
Jorge wrote:

> Thomas 'PointedEars' Lahn wrote:
>> kangax wrote:
>> > Think about what happens when `{ hasOwnProperty: null }` is passed to
>> > `addProperties` method.
>>
>> Nobody sane would create such an object either, or pass a reference to it
^^^^^^^^^^^
>> to this method.
>
> LOL.
>
> Object.prototype.hasOwnProperty.call({ hasOwnProperty: null },
> "hasOwnProperty");
> --> true

q.e.d.


PointedEars
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