I think you may have mixed up a few things:
1. JSON does not recognize '__proto__' per its unchanging spec, and so
parsing that identifier makes an own data property.
2. var obj = {__proto__: proto}; is a special form, unlike any other
identifier __proto__ as the literal property name does assign (set) not
a define.
3. Annex B.2.2.1 defines an accessor on Object.prototype, which if
unshadowed will be got or set when used by name on objects that actually
delegate to Object.prototype. It's also delete-able (configurable),
important for SES and the like.
/be
Andrea Giammarchi <mailto:andrea.giammar...@gmail.com>
October 14, 2013 1:53 PM
`JSON` serialization <= `JSON` parse
Andrea Giammarchi <mailto:andrea.giammar...@gmail.com>
October 14, 2013 1:53 PM
Then I might have confused what decided with `JSON` serialization
where `"__proto__"` will be a property and not a setter, neither a
getter once deserialized.
Is this correct? Yeah, I remember that different accessors looked
weird to me too ... thanks for clarification.
Best Regards
Brendan Eich <mailto:bren...@mozilla.com>
October 14, 2013 1:43 PM
What you just wrote is not true of __proto__ in SpiderMonkey or other
engines I can test (V8, JSC).
It also can't be true via ES6 Annex B, since obj[key] and obj.foo
where key = 'foo' both lookup prototype properties and will find
Object.prototype.foo.
/be
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Andrea Giammarchi <mailto:andrea.giammar...@gmail.com>
October 14, 2013 1:32 PM
I meant that IIRC `obj["__proto__"]` should not invoke that Annex B
specified getter (@Benjamin, Annex B is where you'll find everything
related indeed) but `obj.__proto__` will ... unless once again I've
missed some update.
Yeah, I know that you link stuff, and glad you made some time for
extra clarification.
Cheers
Brendan Eich <mailto:bren...@mozilla.com>
October 14, 2013 1:22 PM
Andrea Giammarchi wrote:
__Current Status__
(Thanks for the dunders! :-P)
Instead of formalizing its form, ES6 accepted `Object.setPrototypeOf`
as described in specs and decided to silently move beside, but still
have in specs, the dunder `__proto__` form, fixing at least a couple
of related gotchas so that:
* unless explicitly set as property, `__proto__` is a named
property for every object that should not affect inheritance so that
`obj["__proto__"]` or `obj[key]` where `key` is the string
`"__proto__"` should not hot/swap the prototypal chain
I'm not sure what you mean here, but first, __proto__ is not specified
in ES6 drafts as an own property. See
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-B.2.2.1
B.2.2.1
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-object.prototype.__proto__>
Object.prototype.__proto__
Object.prototype.__proto__ is an accessor property with attributes {
[[Enumerable]]: false, [[Configurable]]: true }. The [[Get]] and
[[Set]] attributes are defined as follows
B.2.2.1.1
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-get-object.prototype.__proto__>
get Object.prototype.__proto__
The value of the [[Get]] attribute is a built-in function that
requires no arguments. It performs the following steps:
1. Let /O/ be the result of calling ToObject
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-toobject>
passing the *this* value as the argument.
2. ReturnIfAbrupt
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-returnifabrupt>(/O/).
3. Return the result of calling the [[GetPrototypeOf]] internal
method of /O/.
B.2.2.1.2
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-set-object.prototype.__proto__>
set Object.prototype.__proto__
The value of the [[Set]] attribute is a built-in function that takes
an argument proto. It performs the following steps:
1. Let /O/ be CheckObjectCoercible
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-checkobjectcoercible>(*this*
value)/./
2. ReturnIfAbrupt
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-returnifabrupt>(/O/).
3. If Type
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-ecmascript-data-types-and-values>(/proto/)
is neither Object or Null, then return /proto/.
4. If Type
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-ecmascript-data-types-and-values>(/O)/
is not Object, then return /proto/.
5. Let /status/ be the result of calling the [[SetPrototypeOf]]
internal method of /O/ with argument /proto/.
6. ReturnIfAbrupt
<http://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-returnifabrupt>(/status/).
7. If /status/ is *false*, then throw a *TypeError* exception.
8. Return /proto/.
/be
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