JavaScript and XML

You can create an empty (except for an optional root element) XML Document in Firefox and related browsers with the DOM Level 2 method document.implementation.createDocument() . You can accomplish a similar thing in IE with the ActiveX object named MSXML2.DOMDocument. Example 21-1 defines an XML.newDocument() utility function that hides the differences between these two approaches. An empty XML document isn’t useful by itself, but creating one is the first step of the document loading and parsing techniques that are shown in the examples that follow this one.

Example 21-1. Creating an empty XML document

/**
 * Create a new Document object. If no arguments are specified,
 * the document will be empty. If a root tag is specified, the document
 * will contain that single root tag. If the root tag has a namespace
 * prefix, the second argument must specify the URL that identifies the
 *namespace.
 * /
XML.newDocument = function(rootTagName, namespaceURL) {
    if (!rootTagName) rootTagName = "";
    if (!namespaceURL) namespaceURL = "";

    if (document.implementation && document.implementation.createDocument) {
        // This is the W3C standard way to do it
        return document.implementation.createDocument(namespaceURL, 
                       rootTagName, null);
    }
    else { // This is the IE way to do it
        // Create an empty document as an ActiveX object
        // If there is no root element, this is all we have to do
        var doc = new ActiveXObject("MSXML2.DOMDocument");

        // If there is a root tag, initialize the document
        if (rootTagName) {
            // Look for a namespace prefix
            var prefix = "";
            var tagname = rootTagName;
            var p = rootTagName.indexOf(':');
            if (p != -1) {
                prefix = rootTagName.substring(0, p);
                tagname = rootTagName.substring(p+1);
            }

            // If we have a namespace, we must have a namespace prefix
            // If we don't have a namespace, we discard any prefix
            if (namespaceURL) {
                if (!prefix) prefix = "a0"; // What Firefox uses
            }
            else prefix = "";

            // Create the root element (with optional namespace) as a
            // string of text
            var text = "<" + (prefix?(prefix+":"):"") + tagname +
                (namespaceURL
                 ?(" xmlns:" + prefix + '="' + namespaceURL +'"')
                 :"") +
                "/>";
            // And parse that text into the empty document
            doc.loadXML(text);
        }
        return doc;
    }
};