Proxying built-ins (Was: [[Invoke]] and implicit method calls)

David Bruant bruant.d at
Wed Sep 25 14:33:58 PDT 2013

Le 25/09/2013 22:00, Boris Zbarsky a écrit :
> On 9/25/13 3:47 PM, Mark S. Miller wrote:
>> Hi Boris, I don't understand what you mean by "in general". I think the
>> SpiderMonkey use of cross-realm membranes is a great use case for
>> membranes, and I don't understand why they need any special logic at all
>> -- beyond the logic expressed by their handlers, which must include
>> revocation.
> Mark,
> The issue is that if I have access to a different-realm Location 
> object called "loc", say, then:
>   Object.getOwnPropertyDescriptor(Location.prototype, 
> "href")
> should throw if the "loc" is not same-origin with me.
> But:
> Object.getOwnPropertyDescriptor(Location.prototype, 
> "href"), "whatever")
> should perform the set.
This line looks very WebIDL-ish. Does the web really need that to work?
Isn't it a case of WebIDL being overzealous?

> (There are actually some more complications here for the specific case 
> of Location, but let's ignore them for now.)
> What that means in practice is that the membrane isn't actually 
> "revoked": it needs to be unwrapped to the real underlying object in 
> some cases, but not others.
> The way we implement that, again, is with a way to unconditionally 
> unwrap a cross-realm membrane, and a way to ask a cross-realm membrane 
> whether it's ok to unwrap it.
What are the other such cases that require this check?


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