getAttribute('xmlns') returns NULL when using the new DOM API

[ausi]

getAttribute('xmlns') returns NULL when using the new DOM API

[nielsdos]

The new behaviour is the right behaviour, and also how browsers behave.

When you create an element in a namespace, it doesn't add an xmlns attribute into the document tree. Therefore, getAttribute('xmlns') returns NULL. The serializer invoked via saveXML() adds an xmlns attribute in its string output such that the namespace is preserved when parsing the output. However, the attribute is still not added in the document tree.

When you now reload the document by parsing the output from saveXML(), the attribute will be added to the document tree because the input string had the attribute.

You can check this is the same what your browser does:

doc = document.implementation.createDocument('', '');
doc.appendChild(doc.createElementNS('http://www.w3.org/2000/svg', 'svg'));
console.log(doc.firstChild.getAttribute('xmlns')) // returns null
console.log( (new XMLSerializer).serializeToString(doc) ) // now it adds the xmlns attribute in the output, but it still doesn't exist in the document

The "old DOM" behaviour is wrong: it mixes the concept of an internally defined namespaces with attributes that are observable.

I’d have expected that serializing and parsing produces an identical state of the document, but it didn’t.

There are multiple cases where the use of namespaces can lead to invalid XML, and so there are rules that are laid out by the spec on how to make the serializer resolve these issues.

[nielsdos]

BTW If your intention is to get the default namespace in a certain context node, you can use lookupNamespaceURI.

[nielsdos]

Makes sense. Next time I will cross check with the browser behavior in advance. ☺️

FTR: I don't mind answering questions if anything is unclear or seems off though. :-)

[ausi]

Thank you for the detailed explanation!

You can check this is the same what your browser does

Makes sense. Next time I will cross check with the browser behavior in advance. ☺️