The Node.isDefaultNamespace() method accepts a namespace URI as an argument and returns a Boolean with a value of true if the namespace is the default namespace on the given node or false if not.
Syntax
result = node.isDefaultNamespace(namespaceURI)
resultholds the return valuetrueorfalse.namespaceURIis a string representing the namespace against which the element will be checked.
Example
var XULNS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"; var el = document.getElementsByTagNameNS(XULNS, 'textbox')[0]; alert(el.isDefaultNamespace(XULNS)); // true