Web/API/Attr/namespaceURI

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

Before DOM4 this API was defined within the Node interface.

Syntax

namespace = attribute.namespaceURI

Example

In this snippet, an attribute is being examined for its localName and its namespaceURI. If the namespaceURI returns the XUL namespace and the localName returns "browser", then the node is understood to be a XUL <browser/>.

if (attribute.localName == "value" && 
    attribute.namespaceURI == "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul") {
  // this is a XUL value 
}

Notes

This is not a computed value that is the result of a namespace lookup based on an examination of the namespace declarations in scope. The namespace URI of an attribute is frozen at the attribute creation time.

In Firefox 3.5 and earlier, the namespace URI for HTML attributes in HTML documents is null. In later versions, in compliance with HTML5, it is https://www.w3.org/1999/xhtml as in XHTML.

You can create an attribute with the specified namespaceURI using the DOM Level 2 method Element.setAttributeNS.

Per the Namespaces in XML specification, 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 DOM does not handle or enforce namespace validation per se. It is up to the DOM application to do any validation necessary. Note too that the namespace prefix, once it is associated with a particular node, cannot be changed.

Specifications

Specification	Status	Comment
DOMThe definition of 'Attr: namespaceURI' in that specification.	Living Standard

Browser compatibility

Update compatibility data on GitHub

	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
`namespaceURI`	Chrome Full support 46 Notes' Full support 46 Notes' Notes' This API was previously available on the `Node` API.	Edge Full support ≤18	Firefox Full support 48 Notes' Full support 48 Notes' Notes' This API was previously available on the `Node` API.	IE No support No	Opera Full support 33 Notes' Full support 33 Notes' Notes' This API was previously available on the `Node` API.	Safari Full support 1.3	WebView Android Full support 46 Notes' Full support 46 Notes' Notes' This API was previously available on the `Node` API.	Chrome Android Full support 46 Notes' Full support 46 Notes' Notes' This API was previously available on the `Node` API.	Firefox Android Full support 48 Notes' Full support 48 Notes' Notes' This API was previously available on the `Node` API.	Opera Android Full support 33 Notes' Full support 33 Notes' Notes' This API was previously available on the `Node` API.	Safari iOS Full support 1	Samsung Internet Android Full support 5.0 Notes' Full support 5.0 Notes' Notes' This API was previously available on the `Node` API.

Legend

Full support: Full support
No support: No support
See implementation notes.': See implementation notes.