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.


namespace = attribute.namespaceURI


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 == "") {
  // this is a XUL value 


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 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.


Specification Status Comment
The definition of 'Element.namespaceuri' in that specification.
Obsolete Initial definition

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support461 ?481 ? Yes ?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support ? ? ?481 ? ? ?

1. This API was previously available on the Node API.

See also

Document Tags and Contributors

Contributors to this page: connorshea, mattwojo, Sebastianz
Last updated by: connorshea,