A DOM use case that can't be emulated with direct proxies

Brendan Eich brendan at mozilla.com
Fri Dec 14 10:19:51 PST 2012

David Bruant wrote:
> Le 14/12/2012 08:25, Brendan Eich a écrit :
>> window.location can be set by assignment to navigate to a new URL.
> location is [Unforgeable, PutForward], so it should be reflected as a 
> non-configurable getter+setter according to WebIDL.

That would be correct -- and nice, I agree.

>> Yet it appears in Chrome, Firefox, Opera, and Safari to be a writable 
>> data property.
> oh, web browsers and standards...
> There is indeed a pretty violent mismatch between WebIDL and reality, 
> I guess. Specifically because of the behavior you're describing 
> (assigning window.location having a behavior), location ought to be an 
> accessor.
> What was the rationale that motivated all these browsers to go for 
> data property? Is it still time to change this behavior?

Let's not make the standards-are-prior-to-implementations mistake. All 
this came from Netscape 2, JS1. It got cloned by IE and other browsers. 
It mutated and was not standardized until a decade later, in HTML5 and 
then DOM4 -- and WebIDL is an even later (still not REC, it's in CR if I 
recall correctly) standard.

Nevertheless, since ES5-standard reflection is new, I doubt anyone cares 
that location appears to be a data property. It should be an accessor. 
But it needs to be non-configurable, so we still have a problem -- or do we?


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