Provide getAttributeNames() which returns an Array<DOMString>

[esprehn]

Element.prototype.attributes requires allocating all the Attr node instances and the NamedNodeMap itself which is expensive, lots of frameworks (ex. Polymer, Angular, others) just want to iterate the attributes at construction time of an element or when traversing the document and don't need these expensive persistent structures.

Instead we should provide getAttributeNames(), then authors can use that with getAttribute/setAttribute/removeAttribute which results in better memory usage and performance.

This would also get developers to stop using .attributes which means the usage of the exotic Node like thing would go down possibly allowing the removal of it in the future.

@domenic @foolip

[foolip]

That sounds pretty nice, not unlike Object.getOwnPropertyNames.

My biggest question mark is around namespaces, without which this would be a simple API. Because of them, one can't return an array of strings where each string points to a unique attribute:

var e = document.createElement('span');
e.setAttributeNS('http://a.example.com/', 'foo', 'bar');
e.setAttributeNS('http://b.example.com/', 'foo', 'baz');
alert(e.getAttribute('foo'));
e.removeAttribute('foo');
alert(e.getAttribute('foo'));

I'm sure you could come up with a crazy case involving prefixes too.

Should the API throw an exception if any of the attributes are in a namespace, or return a tuple of strings instead of a string for those cases?

[annevk]

I think we should just return the qualified names, those are the property names NamedNodeMap already exposes and what most algorithms operate on.

If you just stick to namespaceless attributes as you should, there will be no issue.

[foolip]

With qualified names you could still have the same string appear multiple times, do we just live with that? It would be nice if one didn't have to resort to NamedNodeMap to guarantee that all attributes are found, but I see no other way to give that guarantee than to have a namespace+localName tuple :(

[annevk]

Yeah, and to be fair, for mutation observers we do care about all attributes. Perhaps we should return an array of two-item-arrays ([namespace, localName])?

[foolip]

That would certainly do the job, although it's unfortunate to waste memory on those arrays for the vast majority of attributes that aren't in a namespace. A mixture of strings and arrays isn't exactly perfect, either.

Any preferences, @esprehn?

[annevk]

The alternative is to continue with precedent: getAttributeNames() and getAttributeNamesNS(). Such joy.

[foolip]

Joy indeed, but that would probably work. One would lose the order between the two sets of attributes, but I'm not sure if that could possibly matter.

[foolip]

To clarify, with the attributes API one can see if an attribute with a namespace comes before an attribute without a namespace and vice versa.

[zcorpan]

The naming conflict issue is already there when using getAttribute(attributes[n].name). If people cared about it, they would use NS methods everywhere, but it seems like it's not really a problem.

[foolip]

@annevk clarified getAttributeNames() and getAttributeNamesNS() on IRC, both would return all attributes. I was assuming that the attributes would be split into two buckets.

[domenic]

I'd prefer just getAttributeNames() and wait for someone to ask for getAttributeNamesNS()...

[foolip]

I'd be OK with that, if the spec has a note saying that it's not guaranteed that the values will be unique, so you can't use it to implement something like Live DOM Viewer.

[annevk]

Yeah, this all sounds good. @smaug----, any concerns?

[smaug----]

So getAttributeNames() would return a new sequence each time?
Are we concerned about silly usage like
for (var i = 0; i < elem.getAttributeNames().length; ++i) {
// do something with elem.getAttributeNames()[i];
}

It is just that .attributes doesn't change, so fewer new objects there.

Would something like
readonly attribute FrozenArray attributeNames;
work, and in such way that it is replaced with a new array whenever an attribute is added or removed?

But I don't object getAttributeNames().