摘要：函數接收三個參數上下文節點表達式和可選的命名空間對象。命名空間對象應該是下面這種字面量的形式。使用樣式表轉換文檔跨瀏覽器使用這個函數接收兩個參數要執行轉換的上下文節點和文檔對象。

本章主要講解了以下四個問題：

跨瀏覽器把XML解析為DOM文檔:

function parseXml(xml){
            var xmldom = null;
            
            if (typeof DOMParser != "undefined"){
                xmldom = (new DOMParser()).parseFromString(xml, "text/xml");
                var errors = xmldom.getElementsByTagName("parsererror");
                if (errors.length){
                    throw new Error("XML parsing error:" + errors[0].textContent);
                }        
            } else if (typeof ActiveXObject != "undefined"){
                xmldom = createDocument();
                xmldom.loadXML(xml);
                if (xmldom.parseError != 0){
                    throw new Error("XML parsing error: " + xmldom.parseError.reason);
                }
            } else {
                throw new Error("No XML parser available.");
            }
            
            return xmldom;
        }
  

這個 parseXml()函數只接收一個參數，即可解析的 XML 字符串。

跨瀏覽器將DOM文檔序列化為XML文檔:

function serializeXml(xmldom){
           
            if (typeof XMLSerializer != "undefined"){
                return (new XMLSerializer()).serializeToString(xmldom);
            } else if (typeof xmldom.xml != "undefined"){
                return xmldom.xml;
            } else {
                throw new Error("Could not serialize XML DOM.");
            }
        }

這個 serializeXml()函數接收一個參數，即要序列化的 XML DOM 文檔。

跨瀏覽器使用XPath:
重新創建 selectSingleNode()和selectNodes()方法。函數接收三個參數：上下文節點、 XPath表達式和可選的命名空間對象。命名空間對象應該是下面這種字面量的形式。

{
    prefix1: "uri1",
    prefix2: "uri2",
    prefix3: "uri3"
}

 function selectSingleNode(context, expression, namespaces){
            var doc = (context.nodeType != 9 ? context.ownerDocument : context);
            
            if (typeof doc.evaluate != "undefined"){
                var nsresolver = null;
                if (namespaces instanceof Object){
                    nsresolver = function(prefix){
                        return namespaces[prefix];
                    };
                }
                
                var result = doc.evaluate(expression, context, nsresolver, XPathResult.FIRST_ORDERED_NODE_TYPE,null);
                return (result !== null ? result.singleNodeValue : null);
            
            } else if (typeof context.selectSingleNode != "undefined"){

                //create namespace string
                if (namespaces instanceof Object){
                    var ns = "";
                    for (var prefix in namespaces){
                        if (namespaces.hasOwnProperty(prefix)){
                            ns += "xmlns:" + prefix + "="" + namespaces[prefix] + "" ";
                        }
                    }
                    doc.setProperty("SelectionNamespaces", ns);
                }
                return context.selectSingleNode(expression);
            } else {
                throw new Error("No XPath engine found.");
            }
        }
        
var result = selectSingleNode(xmldom.documentElement, "wrox:book/wrox:author", { wrox: "http://www.wrox.com/" });            
alert(serializeXml(result));

function selectNodes(context, expression, namespaces){
            var doc = (context.nodeType != 9 ? context.ownerDocument : context);
            
            if (typeof doc.evaluate != "undefined"){
                var nsresolver = null;
                if (namespaces instanceof Object){
                    nsresolver = function(prefix){
                        return namespaces[prefix];
                    };
                }
                
                var result = doc.evaluate(expression, context, nsresolver, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
                var nodes = new Array();
                
                if (result !== null){
                    for (var i=0, len=result.snapshotLength; i < len; i++){
                        nodes.push(result.snapshotItem(i));
                    }
                }
                
                return nodes;
            } else if (typeof context.selectNodes != "undefined"){

                //create namespace string
                if (namespaces instanceof Object){
                    var ns = "";
                    for (var prefix in namespaces){
                        if (namespaces.hasOwnProperty(prefix)){
                            ns += "xmlns:" + prefix + "="" + namespaces[prefix] + "" ";
                        }
                    }
                    doc.setProperty("SelectionNamespaces", ns);
                }
                var result = context.selectNodes(expression);
                var nodes = new Array();
                
                for (var i=0,len=result.length; i < len; i++){
                    nodes.push(result[i]);
                }
                
                return nodes;
            } else {
                throw new Error("No XPath engine found.");
            }
        }
        
var result = selectNodes(xmldom.documentElement, "wrox:book/wrox:author", { wrox: "http://www.wrox.com/" });            
alert(result.length); 

跨瀏覽器使用XSLT：

function transform(context, xslt){
                if (typeof XSLTProcessor != "undefined"){
                    var processor = new XSLTProcessor();
                    processor.importStylesheet(xslt);
            
                    var result = processor.transformToDocument(context);
                    return (new XMLSerializer()).serializeToString(result);
            
                } else if (typeof context.transformNode != "undefined") {
                    return context.transformNode(xslt);
                } else {
                    throw new Error("No XSLT processor available.");
                }
            }

這個 transform()函數接收兩個參數：要執行轉換的上下文節點和 XSLT 文檔對象。