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Re: typeof document.all

From: <hallvord@opera.com>
Date: Tue, 13 Oct 2009 22:08:50 +0000
Message-ID: <20091013220850.waf1dvzclb4kcwo8@staff.opera.com>
To: Brendan Eich <brendan@mozilla.org>
Cc: Anne van Kesteren <annevk@opera.com>, Maciej Stachowiak <mjs@apple.com>, HTML WG <public-html@w3.org>
>> I didn't quite understand the comment about "treating assignment as  
>>  'detecting'" because we do no such thing.
> The jaron is odd, but you do. A "detecting" use of document.all would be
> if (document.all) { IE-only content here }
> We found (see the links in
> https://bugzilla.mozilla.org/show_bug.cgi?id=259935#c0 ) that content
> also did
>  d=document;
>  this.ie=(d.all);
> and so assignment is "detecting" too, and does *not* detect the
> document.all collection.

Isn't the situation here that the variable d just references the real  
document object, so that d.all in turn references the real all  
collection, which this.ie again is going to be a reference too. So  
when this.ie later is used in a boolean context, it refers to the  
same, old doc.all object with its magic "pretend to be false in  
boolean contexts" behaviour.

> wondering if using undefined instead of false as the masquerade value
> would not be even better, since undefined is falsy but also compares
> == itself and null.

Quite possibly.

-Hallvord R.
Received on Tuesday, 13 October 2009 22:09:29 UTC

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