[whatwg] HTML 5 : Misconceptions Documented

Maciej Stachowiak mjs at apple.com
Wed Aug 6 02:29:14 PDT 2008

On Aug 6, 2008, at 12:27 AM, Cameron McCormack wrote:

> Hi Garrett.
> Garrett Smith:
>> In EcmaScript, the property access operators seem to look like a
>> "getter" to Cameron. What they really do is provide access to
>> properties added to the collection, or, in one case (on one
>> implementation), this seems implemented as a "getter". A "getter"  
>> is a
>> method that gets the value of a property of that name.
> I’m sorry I haven’t had a chance to reply yet, I’ve been quite busy  
> with
> other things and haven’t had a chance to work on Web IDL for the last
> few weeks.  (Actually I had a half written reply to your earlier mail
> drafted, but I hadn’t got to finishing it yet.)
> Your tests do show that the HTML collections expose items through real
> properties rather than “fake” ones returned through a custom [[Get]].
> So yes that means that HTML 5 won’t be able to use [IndexGetter]  
> etc. to
> accurately describe current browser behaviour.  That doesn’t  
> necessarily
> mean that [IndexGetter] etc. will have to be changed, just that for  
> the
> purpose of documenting HTML collections they’re insufficient.

I think Garret has a valid point (despite his needlessly rude tone)  
that the way we describe magical dynamic properties in a way that  
makes clear they are also visible to the "in" operator and to  
Object.prototype.hasOwnProperty. Are there any DOM bindings that have  
index (or named) properties which are *not* visible in such a way? If  
not, then the current [IndexGetter] definition is useless and we need  
a better formalism.

> I think that Web IDL can’t provide as much syntactic help for HTML
> collections where the properties are real.  So HTML will probably have
> to include a sentence such as:

I also don't understand what is meant to by calling some properties  
"real". I don't think this is a meaningful distinction. The core of  
the point that Garret raised (as far as I can tell) is that the  
properties are visible to has/in checks as well as gettable, and I  
think this is true in all cases of DOM objects with dynamic index/ 
named properties.

>  In the ECMAScript language binding, for every node in the collection
>  there must exist a property on the collection object whose name is
>  the index of the node in the collection, and whose value is the node.
> With some wording about whether these extra properties take precedence
> over other properties on the object due to the interface, etc.  Ian?

I think Web IDL should provide a formalism to cater to this, because  
nearly all bindings with special dynamic properties work like this  
afaik. But I think it would have to involve a pseudo-method for the  
"hasOwnProperty" check (which "in" is based on).


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