Subj : for each (var property in DOMCollectionObject) causes exception
To   : netscape.public.mozilla.dom,netscape.public.mozilla.jseng
From : Martin Honnen
Date : Sun Jan 30 2005 08:01 pm

Intentionally crossposted to jseng and dom as it is an issue with the 
for each loop e4x adds to JavaScript but the error occurs with a loop on 
a dom object.

The test case at
<http://home.arcor.de/martin.honnen/mozillaBugs/e4x/foreachincollection.html>
tries both a
   for (var propertyName in collection)
and a
   for each (var property in collection)
on a DOM collection (result of getElementsByTagName).
The for each loop enumerates two properties but then throws an error as 
follows in the JavaScript console:

Error: uncaught exception: [Exception... "Illegal operation on 
WrappedNative prototype object"  nsresult: "0x8057000c 
(NS_ERROR_XPC_BAD_OP_ON_WN_PROTO)"  location: "JS frame :: 
http://home.arcor.de/martin.honnen/mozillaBugs/e4x/foreachincollection.html 
:: showProperties :: line 17"  data: no]

If the order of properties enumerated by for in and for each in is the 
same then the error occurs for the property with name 'length'.

Is the error a bug? On which component (JavaScript engine, DOM, or other 
(XPConnect)) should I file it?

Error occurs with latest Mozilla 1.8b (Mozilla/5.0 (Windows; U; Windows 
NT 5.1; en-US; rv:1.8b) Gecko/20050130) but also with earlier builds.


-- 

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

.