Element.setAttributeNS()

setAttributeNS adds a new attribute or changes the value of an attribute with the given namespace and name.

Syntax

element.setAttributeNS(namespace, name, value)

namespace is a string specifying the namespace of the attribute.
name is a string identifying the attribute by its qualified name; that is, a namespace prefix followed by a colon followed by a local name.
value is the desired string value of the new attribute.

let d = document.getElementById('d1'); 
d.setAttributeNS('http://www.mozilla.org/ns/specialspace', 'spec:align', 'center');

DOM methods dealing with element's attributes:

Not namespace-aware, most commonly used methods	Namespace-aware variants (DOM Level 2)	DOM Level 1 methods for dealing with `Attr` nodes directly (seldom used)	DOM Level 2 namespace-aware methods for dealing with `Attr` nodes directly (seldom used)
`setAttribute` (DOM 1)	`setAttributeNS`	`setAttributeNode`	`setAttributeNodeNS`
`getAttribute` (DOM 1)	`getAttributeNS`	`getAttributeNode`	`getAttributeNodeNS`
`hasAttribute` (DOM 2)	`hasAttributeNS`	-	-
`removeAttribute` (DOM 1)	`removeAttributeNS`	`removeAttributeNode`	-

setAttributeNS is the only method for namespaced attributes which expects the fully qualified name, i.e. "namespace:localname".

Specification	Status	Comment
DOM The definition of 'document.setAttributeNS' in that specification.	Living Standard

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`setAttributeNS`	Chrome Full support Yes	Edge Full support 12	Firefox Full support Yes	IE Full support Yes	Opera Full support Yes	Safari Full support 6	WebView Android Full support Yes	Chrome Android Full support Yes	Firefox Android Full support Yes	Opera Android Full support Yes	Safari iOS Full support Yes	Samsung Internet Android Full support Yes