Node: lookupNamespaceURI() method

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 lookupNamespaceURI() method of the Node interface takes a prefix as parameter and returns the namespace URI associated with it on the given node if found (and null if not). This method's existence allows Node objects to be passed as a namespace resolver to XPathEvaluator.createExpression() and XPathEvaluator.evaluate().

Syntax

lookupNamespaceURI(prefix)

Parameters

prefix: The prefix to look for. The empty string is equivalent to null, meaning the default namespace.

Note: This parameter is not optional, but can be set to null.

Return value

A string containing the namespace URI corresponding to the prefix.

Always returns null if the node is a DocumentFragment, DocumentType, Document with no documentElement, or Attr with no associated element.
If prefix is "xml", the return value is always "http://www.w3.org/XML/1998/namespace".
If prefix is "xmlns", the return value is always "http://www.w3.org/2000/xmlns/".
If the prefix is null, the return value is the default namespace URI.
If the prefix is not found, the return value is null.

Example

Note: This example runs in an HTML document, where xmlns: attributes are ignored (except xmlns:xlink). Firefox sets all elements' namespace URIs to null, while Chrome and Safari appropriately set HTML, SVG, and MathML elements' default namespace URIs. If you want to conduct more meaningful tests, you can open a standalone SVG document and execute scripts in its context.

html

<div class="hidden">
  <div>Test HTML element</div>
  <svg>
    <text>Test SVG element</text>
  </svg>
  <svg xmlns:xlink="http://www.w3.org/1999/xlink" id="with-xlink">
    <text>Test SVG element with xlink</text>
  </svg>
  <math>Test MathML element</math>
</div>

<table>
  <thead>
    <tr>
      <th><code>prefix</code></th>
      <th><code>&lt;div&gt;</code></th>
      <th><code>&lt;svg&gt;</code></th>
      <th><code>&lt;svg xmlns:xlink&gt;</code></th>
      <th><code>&lt;math&gt;</code></th>
    </tr>
  </thead>
  <tbody></tbody>
</table>

.hidden {
  display: none;
}

const htmlElt = document.querySelector("div");
const svgElt = document.querySelector("svg");
const svgEltXLink = document.querySelector("#with-xlink");
const mathElt = document.querySelector("math");

const tbody = document.querySelector("tbody");

for (const prefix of ["xmlns", "xml", "html", "svg", "xlink", "", null]) {
  const row = document.createElement("tr");
  tbody.appendChild(row);
  row.appendChild(document.createElement("td")).textContent =
    JSON.stringify(prefix);
  for (const el of [htmlElt, svgElt, svgEltXLink, mathElt]) {
    console.log(el, prefix, el.lookupNamespaceURI(prefix));
    row.appendChild(document.createElement("td")).textContent = String(
      el.lookupNamespaceURI(prefix),
    );
  }
}

Specifications

Specification
DOM # dom-node-lookupnamespaceuri

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
`lookupNamespaceURI`	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 3 (Release date: 2007-10-26) 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

Tip: you can click/tap on a cell for more information.

Full support: Full support