Node: lookupPrefix() 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.

The lookupPrefix() method of the Node interface returns a string containing the prefix for a given namespace URI, if present, and null if not. When multiple prefixes are possible, the first prefix is returned.

Syntax

js
lookupPrefix(namespace)

Parameters

namespace

A string containing the namespace to look the prefix up.

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

Return value

A string containing the corresponding prefix, or null if none has been found. If namespace is null, or the empty string, lookupPrefix() returns null.

If the node is a DocumentType or a DocumentFragment, lookupPrefix() always returns null.

Example

html
Prefix for <code>http://www.w3.org/2000/svg</code> on &lt;output&gt;:
<output>Not tested</output>.<br />
Prefix for <code>http://www.w3.org/XML/1998/namespace</code> on &lt;output&gt;:
<output>Not tested</output>.<br />
Prefix for <code>http://www.w3.org/TR/html4/</code> on &lt;output&gt;:
<output>Not tested</output>.<br />
Prefix for <code>https://www.w3.org/1999/xlink</code> on &lt;output&gt;:
<output>Not tested</output>.<br />
Prefix for <code>http://www.w3.org/2000/svg</code> on &lt;svg&gt;:
<output>Not tested</output>.<br />
Prefix for <code>https://www.w3.org/1999/xlink</code> on &lt;svg&gt;:
<output>Not tested</output>.<br />
Prefix for <code>http://www.w3.org/XML/1998/namespace</code> on &lt;svg&gt;:
<output>Not tested</output>.<br />
<svg xmlns:t="http://www.w3.org/2000/svg" height="1"></svg>
<button>Click to see the results</button>
js
const button = document.querySelector("button");
button.addEventListener("click", () => {
  const aHtmlElt = document.querySelector("output");
  const aSvgElt = document.querySelector("svg");

  const result = document.getElementsByTagName("output");
  result[0].value = aHtmlElt.lookupPrefix("http://www.w3.org/2000/svg"); // true
  result[1].value = aHtmlElt.lookupPrefix(
    "http://www.w3.org/XML/1998/namespace",
  ); // false
  result[2].value = aHtmlElt.lookupPrefix("http://www.w3.org/TR/html4/"); // true
  result[3].value = aHtmlElt.lookupPrefix("https://www.w3.org/1999/xlink"); // false
  result[4].value = aSvgElt.lookupPrefix("http://www.w3.org/2000/svg"); // true
  result[5].value = aSvgElt.lookupPrefix("https://www.w3.org/1999/xlink"); // true
  result[6].value = aSvgElt.lookupPrefix(
    "http://www.w3.org/XML/1998/namespace",
  ); // false
});

Specifications

Specification
DOM Standard
# dom-node-lookupprefix

Browser compatibility

BCD tables only load in the browser

See also