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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

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

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>

const button = document.querySelector("button");
button.addEventListener("click", () => {
  const htmlElt = document.querySelector("output");
  const svgElt = document.querySelector("svg");

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

Specifications

Specification
DOM> # dom-node-lookupprefix>

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
`lookupPrefix`	1	12	1	≤12.1	3	18	4	≤12.1	1	1.0	4.4	1

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https://developer.mozilla.org/en-US/docs/Web/API/Node/lookupPrefix