Here is an implementation of Node.lookupNamespaceURI which should work cross-browser.
Note that all Gecko-based browsers (including Firefox) support Node.lookupNamespaceURI. This function is not necessary for Gecko-based browsers (though the function will quickly return the standard value for Mozilla browsers) when used to reflect on static documents. However, due to bug 312019, this method does not work with dynamically assigned namespaces (e.g., those set with Node.prefix).
/*globals Document, HTMLDocument */
(function () {
'use strict';
var Doc = typeof Document !== 'undefined' ? Document : HTMLDocument; // Support HTMLDocument if Document not present // If Document is present, is this method also present?
addLookupNamespaceURI(Doc);
addLookupNamespaceURI(Element);
function addLookupNamespaceURI (type) {
if (!type.prototype.lookupNamespaceURI) {
type.prototype.lookupNamespaceURI = lookupNamespaceURI;
}
function lookupNamespaceURI (prefix) {
return lookupNamespaceURIHelper(this, prefix);
}
function lookupNamespaceURIHelper (node, prefix) { // adapted directly from https://www.w3.org/TR/DOM-Level-3-Core/namespaces-algorithms.html#lookupNamespaceURIAlgo
var i, att,
htmlMode = document.contentType, // Mozilla only
xmlnsPattern = /^xmlns:(.*)$/;
switch (node.nodeType) {
case 1: // ELEMENT_NODE (could also just test for Node.ELEMENT_NODE, etc., if supported in all browsers)
if (node.namespaceURI != null && node.prefix === prefix) {
// Note: prefix could be "null" in the case we are looking for default namespace
return node.namespaceURI;
}
if (node.attributes.length) {
for (i = 0; i < node.attributes.length; i++) {
att = node.attributes[i];
if (xmlnsPattern.test(att.name) && xmlnsPattern.exec(att.name)[1] === prefix) {
if (att.value) {
return att.value;
}
return null; // unknown
}
if (att.name === 'xmlns' && prefix == null) {
// default namespace
if (att.value) {
return att.value;
}
return null; // unknown
}
}
}
if (node.parentNode && node.parentNode.nodeType !== 9) {
// EntityReferences may have to be skipped to get to it
return lookupNamespaceURIHelper(node.parentNode, prefix);
}
return null;
case 9: // DOCUMENT_NODE
return lookupNamespaceURIHelper(node.documentElement, prefix);
case 6: // ENTITY_NODE
case 12: // NOTATION_NODE
case 10: // DOCUMENT_TYPE_NODE
case 11: // DOCUMENT_FRAGMENT_NODE
return null; // unknown
case 2: // ATTRIBUTE_NODE
if (node.ownerElement) {
return lookupNamespaceURIHelper(node.ownerElement, prefix);
}
return null; // unknown
default:
// TEXT_NODE (3), CDATA_SECTION_NODE (4), ENTITY_REFERENCE_NODE (5),
// PROCESSING_INSTRUCTION_NODE (7), COMMENT_NODE (8)
if (node.parentNode) {
// EntityReferences may have to be skipped to get to it
return lookupNamespaceURIHelper(node.parentNode, prefix);
}
return null; // unknown
}
};
}
}());