Re: Allow to return same NodeList object for queries like getElementsByTagName, getElementsByClassName and getElementsByName

On Fri, 12 Feb 2010 12:51:03 +0100, Maciej Stachowiak <>  
> On Feb 12, 2010, at 3:47 AM, Maciej Stachowiak wrote:
>> On Feb 12, 2010, at 3:19 AM, Anne van Kesteren wrote:
>>> On Fri, 22 Jan 2010 14:11:40 +0100, Anton Muhin <>  
>>> wrote:
>>>> Is it possible to allow caching for those cases?  Firefox caches those
>>>> node lists for a long time (Maciej found the related bug
>>>>  IE8 caches as
>>>> well.   Opera, Safari and Chrome do not.
>>> Sorry for the somewhat late reply. We'd prefer not to change the  
>>> specification here and keep the requirement. We're afraid of potential  
>>> hard to detect incompatibility bugs if you sometimes cache and  
>>> sometimes don't. We're also not convinced that you cannot get the  
>>> performance win by other means.
>> Since Firefox and IE both cache, how would it create compatibility bugs  
>> for other browsers to do so as well? I think we should remove the  
>> requirement unless Firefox and IE are willing to change their  
>> implementations.

I would hope they fix their bugs in due course, yes. Specifically leaving  
the behavior undefined seems like a bad idea. We know that from other  

> In addition, I should mention that likely the only observable difference  
> is in setting custom ("expando") properties. If you make two equivalent  
> requests for a NodeList, setting a property on one will show up on the  
> other only in the case where there was caching. However, I think use of  
> expando properties on NodeLists is unlikely. Sacrificing a lot of  
> performance for a marginal hypothetical improvement in predictability of  
> behavior does not seem like a good tradeoff.

Is it really a lot of performance? Our developers are not that convinced.

Also it has been suggested to me that just-in-time optimizations might not  
work well if different users start polluting the same object (if nodelists  
are shared).

Anne van Kesteren

Received on Friday, 12 February 2010 13:06:08 UTC