Obsolete
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.

The Node.namespaceURI read-only property returns the namespace URI of the node, or null if the node is not in a namespace. When the node is a document, it returns the XML namespace for the current document.

In DOM4 this API was moved from Node to the Element and Attr interfaces.

Syntax

namespace = node.namespaceURI

Example

In this snippet, a node is being examined for its Node.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 (node.localName == "browser" && 
    node.namespaceURI == "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul") {
  // this is a XUL browser 
}

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 a node is frozen at the node creation time.

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

For nodes of any Node.nodeType other than ELEMENT_NODE and ATTRIBUTE_NODE the value of namespaceURI is always null.

You can create an element with the specified namespaceURI using the DOM Level 2 method Document.createElementNS and attributes with the 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
Document Object Model (DOM) Level 3 Core Specification
The definition of 'Node.namespaceURI' in that specification.
Recommendation Specifies the behavior when it's set to null.
Document Object Model (DOM) Level 2 Core Specification
The definition of 'DOM Level 2 Core: XML Namespaces' in that specification.
Recommendation  
Document Object Model (DOM) Level 2 Core Specification
The definition of 'Node.namespaceURI' in that specification.
Recommendation Initial definition

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes)
No support46.0[1]
(Yes)[2]
No support 48.0 (48.0)[1]
? ? ?
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? (Yes)[2]
No support 48.0 (48.0)[1]
? ? ?

[1] This API was moved to the Element and Attr APIs according to the DOM4 standard.

[2] Prior to Gecko 5.0 (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2), this property was read-write; starting with Gecko 5.0 it is read-only, following the specification.

See also