Internet Explorer, for the most part, implements MSXml 4.0 or higher. However that’s (obviously) a Microsoft technology, and the standard implementation doesn’t support XPath in the DOM.

In particular the selectNodes() and selectSingleNode() functions are of particular use when manipulating XML or the DOM. Using these functions you can parse an XPath expression and get a nodelist of elements in your DOM that match the expression.

The code below adds basic XPath parsing functionality to the DOM in Mozilla. (Thanks to km0ti0n)

// mozXPath - http://km0.la/js/mozXPath/
// km0ti0n@gmail.com
// Code licensed under Creative Commons Attribution-ShareAlike License
// http://creativecommons.org/licenses/by-sa/2.5/
if (document.implementation.hasFeature("XPath", "3.0")) {
	if ( typeof XMLDocument == "undefined" ) {
		XMLDocument = Document;
	}
	XMLDocument.prototype.selectNodes = function(cXPathString, xNode) {
		if ( !xNode ) { xNode = this; }
		var oNSResolver = this.createNSResolver(this.documentElement);
		var aItems = this.evaluate(cXPathString, xNode, oNSResolver, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
		var aResult = [];
		for ( var i = 0; i < aItems.snapshotLength; i++) {
			aResult[i] =  aItems.snapshotItem(i);
		}
		return aResult;
	}
	XMLDocument.prototype.selectSingleNode = function(cXPathString, xNode) {
		if( !xNode ) { xNode = this; }
		var xItems = this.selectNodes(cXPathString, xNode);
		if ( xItems.length > 0 ) { return xItems[0]; }
		else { return null; }
	}

	Element.prototype.selectNodes = function(cXPathString) {
		if (this.ownerDocument.selectNodes) {
			return this.ownerDocument.selectNodes(cXPathString, this);
		} else { throw "For XML Elements Only"; }
	}

	Element.prototype.selectSingleNode = function(cXPathString) {
		if (this.ownerDocument.selectSingleNode) {
			return this.ownerDocument.selectSingleNode(cXPathString, this);
		} else { throw "For XML Elements Only"; }
	}
}

It appears that Opera doesn’t have the XMLDocument object type, so, when using the XmlHttpRequest object the responseXML is in fact a Document object.

To get around this fact, we can use:

if ( typeof XMLDocument == "undefined" ) {
    XMLDocument = Document;
}

To use these new features, in either IE or Firefox, you can now simple call the functions as a method of the elements themselves… e.g.:

On the following XML Document:

    
      Some Content
    
    
      Some Content
    
    
      Some Content
    

For the XML sample above, you can use the following XPath to select all ContentNode’s with their enabled attribute set to “true”:
//subnode[@enabled='true']/contentnode

So you would retrieve your XML Node List by executing the following JavaScript function:

//assume the variable xDOM is an XmlDocument object
//...that has been pre-loaded with the example XML
var nodeList = xDOM.selectNodes('//subnode[@enabled='true']/contentnode');
for each (var xNode in nodeList) {
    //do some operation...
}

This would perform some operation on each contentnode which is inside a subnode with it’s enabled property set to true.

NOTE: Be sure to double check your syntax, spelling and remember XML/XPath is CaseSensitive.