Subj : Re: E4X: calling appendChild method with existing child as the argument
To   : netscape.public.mozilla.jseng
From : Martin Honnen
Date : Sat Apr 09 2005 05:14 pm



Brendan Eich wrote:

> Martin Honnen wrote:
> 
>>
>> In E4X XML objects have a method called appendChild which behaves 
>> differently in regardance to object identity when the method is called 
>> with an existing child as the argument:
>>
>> Spidermonkey:
>>
>> js> var gods = <gods><god>Kibo</god><god>Xibo</god></gods>;
>> js> gods
>> <gods>
>>   <god>Kibo</god>
>>   <god>Xibo</god>
>> </gods>
>> js> gods.appendChild(gods.god[0])
>> <gods>
>>   <god>Kibo</god>
>>   <god>Xibo</god>
>>   <god>Kibo</god>
>> </gods>
>> js> gods.god[0] === gods.god[2]
>> true
> 
> 
> SpiderMonkey is correct if you follow ECMA-357 9.2.1.2 XMLList [[Put]], 
> in particular 2(g)(ii)(2).

If Spidermonkey is correct should it be able to deal with "recursive" 
XML like the following?

var god = <god>Kibo</god>;
var infiniteGod = god.appendChild(god);
print('infiniteGod.nodeKind(): ' + infiniteGod.nodeKind());
print(god.toXMLString());

The Spidermonkey shell runs out of memory on the last line with 
toXMLString():

js> load('mozillaBugs/e4x/recursiveXML1.js');
infiniteGod.nodeKind(): element
mozillaBugs/e4x/recursiveXML1.js:4: out of memory


I have a feeling that such cyclic structures will cause a lot of 
troubles when using E4X. What is going to happen if I have an XML DOM with
   <gods><god>Kibo</god><god>Xibo</god></gods>;
then wrap it with
   var xmlObject = XML(domNode);
and do the
   xmlObject.appendChild(xmlObject.god[0])
In the DOM a node can only be at exactly one position so how would
   xmlObject.domNode()
look then?


-- 

	Martin Honnen
	http://JavaScript.FAQTs.com/

.