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Re: typeof document.all

From: Brendan Eich <brendan@mozilla.org>
Date: Tue, 13 Oct 2009 11:58:57 -0700
Cc: "Maciej Stachowiak" <mjs@apple.com>, "HTML WG" <public-html@w3.org>
Message-Id: <5A59EC84-6320-42D5-989D-EB9A562E48DC@mozilla.org>
To: Anne van Kesteren <annevk@opera.com>
On Oct 13, 2009, at 11:47 AM, Anne van Kesteren wrote:

> On Tue, 13 Oct 2009 20:39:42 +0200, Brendan Eich  
> <brendan@mozilla.org> wrote:
>> On Oct 13, 2009, at 11:19 AM, Anne van Kesteren wrote:
>>> typeof gives undefined and ToBoolean gives false. I'm not sure  
>>> there's anything else.
>>
>> What about (document.all == undefined) and (document.all == null)?  
>> How about ===? These do not apply ToBoolean.
>
> All false. I haven't seen any logged issues on this either, but  
> admittedly I have not looked into it that much. I'm mostly trying to  
> wrap my head around some other specs.

Okey dokey. :-/

I pinged Chris Pine of Opera, who may still be on leave but may know  
more.


>> How is that not what you called a "weird result"? It's similar to  
>> what we do in assigning undefined, i.e., treating assignment as  
>> "detecting".
>
> Having the object evaluate to false does not seem so weird to me.

Let me get this straight: the only cases where Opera evaluates  
document.all to false are cases in ECMA-262 that apply the ToBoolean  
internal helper. Otherwise it evaluates to a collection.

And typeof document.all == "undefined".

That is simpler than what WebKit does, although as you noted it too  
conflicts with ECMA-262.

But according to bugs I've cited, see

https://bugzilla.mozilla.org/show_bug.cgi?id=253150#c4
https://bugzilla.mozilla.org/show_bug.cgi?id=253150#c12
https://bugzilla.mozilla.org/attachment.cgi?id=154617

it was not, and by default we presume is not, web-compatible.

Indeed Google codesearch discloses:

http://www.google.com/codesearch?hl=en&lr=&q=lang%3Ajavascript+%22.all+%3D%3D+undefined%22&sbtn=Search
http://www.google.com/codesearch?hl=en&lr=&q=lang%3Ajavascript+%22.all+!%3D+undefined%22&sbtn=Search
http://www.google.com/codesearch?hl=en&lr=&q=lang%3Ajavascript+%22.all+%3D%3D+null%22&sbtn=Search
http://www.google.com/codesearch?hl=en&lr=&q=lang%3Ajavascript+%22.all+!%3D+null%22&sbtn=Search

So I don't think what you describe, if that's all Opera does, is  
sufficient, because false != null and false != undefined.

/be
Received on Tuesday, 13 October 2009 19:00:04 UTC

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