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Re: [WebIDL] interface objects and properties too restrictive?

From: Maciej Stachowiak <mjs@apple.com>
Date: Wed, 04 Aug 2010 15:42:33 -0700
Cc: Jonas Sicking <jonas@sicking.cc>, Cameron McCormack <cam@mcc.id.au>, "Sam Weinig (weinig@apple.com)" <weinig@apple.com>, "public-webapps@w3.org" <public-webapps@w3.org>
Message-id: <B00A1A2A-FC91-4B0F-AF39-8C26EBCA9B49@apple.com>
To: Travis Leithead <travil@microsoft.com>

On Aug 4, 2010, at 11:36 AM, Travis Leithead wrote:

> Sure.
> Not only does ES5's configurable: false property prevent deletion, but it also prevents changing a property from a field to an accessor and vice-versa, as well as changing the getter/setters of the property.
> So, the following wouldn't work if the "appendChild" property was configurable:false:
> Object.defineProperty(Node.prototype, 
>                      "appendChild", 
>                      { get: function() { /* custom getter replacement */ }, 
>                        set: function(x) { /* custom setter replacement */ }
>                      });
> ... which is the ES5 way of doing:
> Node.prototype.__defineGetter__("appendChild", function() { /* custom getter replacement */ });
> Node.prototype.__defineSetter__("appendChild", function(x) { /* custom setter replacement */ });
> So, configurable: false prevents users from replacing built-in properties with getter/setters. I think this is too restrictive, especially forward-looking considering how much the DOM is changing and evolving.

I don't see why you would want to do that. The common way to override the behavior of DOM operations is: 

Node.prototype.appendChild = function(node) { /* replacement function */ }

I think what you describe is not commonly done, or particularly useful. Furthermore, prototype hacking is primarily used for additions, not replacements, which are not impacted by this at all.

Likewise, I don't think it's common to want to add a setter for the window.Node global interface object.


> -----Original Message-----
> From: Jonas Sicking [mailto:jonas@sicking.cc] 
> Sent: Tuesday, August 03, 2010 5:22 PM
> To: Travis Leithead
> Cc: Cameron McCormack; Sam Weinig (weinig@apple.com); public-webapps@w3.org
> Subject: Re: [WebIDL] interface objects and properties too restrictive?
> On Tue, Aug 3, 2010 at 4:57 PM, Travis Leithead <travil@microsoft.com> wrote:
>> Hey folks, just wondering what the justification behind the current 
>> {DontDelete} semantics are in WebIDL 4.4 [1] and 4.5 (second bullet) 
>> [2]. When our IE9 binding ported this to ES5, it translated to 
>> "configurable: false", which completely destroyed the ability to set 
>> accessors on the interface objects as well as operations (and in our 
>> case, DOM accessors). Because of this, we actually don't mark our 
>> interface objects OR operations/attributes as configurable: false, 
>> rather configurable: true.*
>> If this seems reasonable, I'd like to see the spec updated.
> Sorry, I'm not very updated on the differences between the ES3 and ES5 worlds. Why does "configurable: false" destroyed the ability to set accessors? Can you give an example of a piece of script that doesn't work but which you'd like to work, and what you'd like it to do?
> / Jonas
Received on Wednesday, 4 August 2010 22:43:07 UTC

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