Element.getAttributeNames() does not match browser behavior

[titouanmathis]

Describe the bug

The Element.getAttributeNames() in happy-dom v16 and v17 does not return the same values as browsers. It is working as expected in happy-dom v15.

To Reproduce

Try the following snippet in a browser console (tested in Firefox 135, Chrome 133 and Safari 18 on macOS):

const element = document.createElement('div');
element.setAttribute('ns1:key', 'value1');
element.setAttribute('ns2:key', 'value1');
element.setAttribute('key1', 'value1');
element.setAttribute('key2', '');

console.log(element.getAttributeNames());
// browser: ['ns1:key', 'ns2:key', 'key1', 'key2']
// happy-dom@17: ['ns2:key', 'key1', 'key2']

I also added a failing test in a fork: titouanmathis@8fba4af.

Expected behavior

happy-dom should return the same attributes as the browser when using the Element.getAttributeNames() method.

Screenshots
Not relevant.

Device:

• OS: macOS
• Browser: firefox
• Version: 135

Additional context

Bug encountered in a vitest environment.