[webkit-dev] What data structure is used to store multiple input controls sharing the same name?

Darin Adler darin at apple.com
Mon Mar 27 12:02:12 PST 2006

On Mar 20, 2006, at 10:13 AM, Marco Wise wrote:

> What kind of data structure/object is used internally by Safari /  
> Konqueror to store multiple inputs with the same name? Is it a  
> NodeList as in IE/Firefox, or something different? Can properties  
> be assigned to this object using Javascript?
> Using the code below it looks like Firefox, IE and Safari create an  
> HTMLInputElement the first time a control named _submit is  
> encountered.
> The second time a control named _submit is encountered, it seems  
> that a data structure is created to hold the HTMLInputElements and  
> these can then be accessed using array notation.
> Firefox/IE report that this new structure is a Nodelist, but Safari  
> only reports that it's an "object". When I try using toString() to  
> get more information but then Safari reports an error that it's not  
> an object.
> Finally,
> In Firefox/IE you can assign new properties to this new Nodelist as  
> in _submit.foo = "bar" and you can retrieve their value.
> In Safari (I'm using 2.0.3) doing so will fail silently and  
> retrieving them will return "undefined".
> The code I'm using to try to sort this out:
> <html>
> <form name="test_form" onsubmit="test(this);">	
> 	<input type="submit" name="_submit" value="One">
> 	<script>
> 	  alert("_submit is a " + document.forms[0]._submit);
> 	  alert("_submit's value is " + document.forms[0]._submit.value);
> 	</script>
> 	<input type="submit" name="_submit" value="Two">
> 	<script>
> 	  alert("_submit is now a " + document.forms[0]._submit);
> 	  alert("_submit's value is now " + document.forms[0]._submit.value);
> 	  alert("Assigning a value to _submit...");
> 	  document.forms[0]._submit.value = "New Value";
> 	  alert("_submit's value is now " + document.forms[0]._submit.value);
> 	  alert("The original _submit's value can still be reached as an  
> item: " + document.forms[0]._submit[0].value);
> 	</script>
> </form>
> </html>
> I've looked at the webkit source code but I'm not an expert at C++  
> so I am not quite sure where to find this information. I've also  
> tried calling functions that should work on Nodelists and arrays on  
> this object and they fail. The only property that seems to work is  
> "length".
> To recap, my question is: how does Safari store multiple input  
> controls that share the same name? Can this object have its own  
> properties (besides "length")?
> Thanks in advance for any help you can provide,

Here are some implementation details. I don't know if they will help  
you solve whatever problem you're working on.

document.forms is an HTMLCollection.

The function used to get an item by name in an HTML collection exists  
only in the JavaScript binding in Safari. It's  
JSHTMLCollection::getNamedItems, in kjs_html.cpp.

The class used when there is more than one item with the same name is  
DOMNamedNodesCollection, defined in kjs_dom.h/cpp. Looking at  
DOMNamedNodesCollection::getOwnPropertySlot, it looks like it  
supports length, indexing by number, and indexing by ID.

Would you consider filing a bug report about the problem you're  

     -- Darin

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