The getAttributeNames() method of the Element interface returns the attribute names of the element as an Array of strings. If the element has no attributes it returns an empty array.

Using getAttributeNames() along with getAttribute(), is a memory-efficient and performant alternative to accessing Element.attributes.

The names returned by getAttributeNames() are qualified attribute names, meaning that attributes with a namespace prefix have their names returned with that namespace prefix (not the actual namespace), followed by a colon, followed by the attribute name (for example, xlink:href), while any attributes which have no namespace prefix have their names returned as-is (for example, href).

None.

None (undefined).

The following example shows how:

• For an attribute which has a namespace prefix, getAttributeNames() returns that namespace prefix along with the attribute name.
• For an attribute which has no namespace prefix, getAttributeNames() returns just the attribute name, as-is.

It's important to understand that:

1. An attribute can be present in the DOM with a namespace but lacking a namespace prefix.
2. For an attribute in the DOM that has a namespace but lacks a namespace prefix, getAttributeNames() will return just the attribute name, with no indication that the attribute is in a namespace.

The example below includes such a "namespaced but without a namespace prefix" case.

const element = document.createElement("a");

// set "href" attribute with no namespace and no namespace prefix
element.setAttribute("href", "https://example.com");
// set "href" attribute with namespace and also "xlink" namespace prefix
element.setAttributeNS(
  "http://www.w3.org/1999/xlink",
  "xlink:href",
  "https://example.com",
);
// set "show" attribute with namespace but no namespace prefix
element.setAttributeNS("http://www.w3.org/1999/xlink", "show", "new");

// Iterate over element's attributes
for (const name of element.getAttributeNames()) {
  const value = element.getAttribute(name);
  console.log(name, value);
}

// logs:
// href https://example.com
// xlink:href https://example.com
// show new