Attr: namespaceURI property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

See full compatibility

The read-only namespaceURI property of the Attr interface returns the namespace URI of the attribute, or null if the element is not in a namespace.

The namespace URI is set at the Attr creation and cannot be changed. An attribute with a namespace can be created using Element.setAttributeNS().

Note: An attribute does not inherit its namespace from the element it is attached to. If an attribute is not explicitly given a namespace, it has no namespace.

The browser does not handle or enforce namespace validation per se. It is up to the JavaScript application to do any necessary validation. Note, too, that the namespace prefix, once it is associated with a particular attribute node, cannot be changed.

Value

A string containing the URI of the namespace, or null if the attribute is not in a namespace.

Example

The following example shows the results for a prefixed attribute in a case of an HTML element, and of a SVG element. As HTML doesn't handle namespaces, it will always return null in that case. In the case of the SVG element, it will return the URI of the XML namespace, http://www.w3.org/XML/1998/namespace.

HTML

html

<svg xml:lang="en-US" class="struct" height="1" width="1">Click me</svg>
<label xml:lang="en-US" class="struct"></label>

<p>
  <button>Show value for &lt;svg&gt;</button>
  <button>Show value for &lt;label&gt;</button>
</p>

<p>
  Namespace URI of the attribute <code>xml:lang</code>:
  <output id="result">None.</output>
</p>

JavaScript

const elements = document.querySelectorAll(".struct");
const buttons = document.querySelectorAll("button");
const outputEl = document.querySelector("#result");

let i = 0;
for (const button of buttons) {
  const element = elements[i];
  button.addEventListener("click", () => {
    const attribute = element.attributes[0];
    outputEl.value = attribute.namespaceURI;
  });
  i++;
}

Specifications

Specification
DOM # dom-attr-namespaceuri

Browser compatibility

	desktop					mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on iOS	Samsung Internet	WebView Android	WebView on iOS
`namespaceURI`	Chrome – Full support Chrome 1 (Release date: 2008-12-11) footnote Full support	Edge – Full support Edge 12 (Release date: 2015-07-29) footnote Full support	Firefox – Full support Firefox 1 (Release date: 2004-11-09) footnote Full support	Opera – Full support Opera 12.1 (Release date: 2012-11-20) footnote Full support	Safari – Full support Safari 1 (Release date: 2003-06-23) footnote Full support	Chrome Android – Full support Chrome Android 18 (Release date: 2012-06-27) footnote Full support	Firefox for Android – Full support Firefox for Android 4 (Release date: 2011-03-29) footnote Full support	Opera Android – Full support Opera Android 12.1 (Release date: 2012-10-09) footnote Full support	Safari on iOS – Full support Safari on iOS 1 (Release date: 2007-06-29) footnote Full support	Samsung Internet – Full support Samsung Internet 1 (Release date: 2013-04-27) footnote Full support	WebView Android – Full support WebView Android 4.4 (Release date: 2013-12-09) footnote Full support	WebView on iOS – Full support WebView on iOS 1 (Release date: 2007-06-29) footnote Full support

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Full support: Full support