var xmlDom = getXMLDOM(xmlStr);//调用之前写好的方法获得XMLDOM对象

        //        var node = xmlDom.selectSingleNode("root/user"); //获取单一节点

        //        alert(node.firstChild.nodeValue);

//        var node = xmlDom.selectSingleNode("root/user/text()"); //text()可以获取节点内的值

        //        alert(node.nodeValue);

        var node = xmlDom.selectSingleNode("//user[1]"); //双斜杠可以获取不关心层次的第一个user

        alert(node.xml);

        var node = xmlDom.selectSingleNode("root/user[@idp=5]");

        //通过唯一属性找到user节点

        alert(node.xml);

//        var nodes = xmlDom.selectNodes("root/user");

//        alert(nodes[1].xml)

    //做兼容，单个节点

    function selectSingleNode(xmlDom, xpath) {

        var node = null;

        //W3C

        if (typeof xmlDom.evaluate != "undefined") {

            /*此处需要将W3C标准，火狐等浏览器下的xpath【数字】加1，从而达到与IE xpath统一*/

            var patten = /\[(\d+)\]/g;

            var flag = xpath.match(patten);

            var num = 0;

            if (flag !== null) {

                num = parseInt(RegExp.$1) + 1;

                xpath = xpath.replace(patten, '[' + num + ']');

            }

            var eva = new XPathEvaluator();

            var result = eva.evaluate(xpath, xmlDom, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null); //单一节点

            if (result !== null) {

                node = result.singleNodeValue;

            }

        }

        else if (typeof xmlDom.selectSingleNode != "undefined") {//IE

            node = xmlDom.selectSingleNode(xpath);

        }

        return node;

    }

   //跨浏览器，做个节点集合

    function selectSingleNodes(xmlDom, xpath) {

        var nodes = null;

        //W3C

        if (typeof xmlDom.evaluate != "undefined") {

            /*此处需要将W3C标准，火狐等浏览器下的xpath【数字】加1，从而达到与IE xpath统一*/

            var patten = /\[(\d+)\]/g;

            var flag = xpath.match(patten);

            var num = 0;

            if (flag !== null) {

                num = parseInt(RegExp.$1) + 1;

                xpath = xpath.replace(patten, '[' + num + ']');

            }

            var eva = new XPathEvaluator();

            var result = eva.evaluate(xpath, xmlDom, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null); //节点集合

            var node = null;

            //下一跳节点

            var nodes = [];

            while ((node = result.iterateNext()) !== null) {

                nodes.push(node);

            }

        }

        else if (typeof xmlDom.selectNodes != "undefined") {//IE

            nodes = xmlDom.selectNodes(xpath);

        }

        return nodes;

    }

    //    alert(serializerXML(selectSingleNodes(xmlDom, "root/user")));

    alert(serializerXML(selectSingleNodes(xmlDom, "root/user")[1]));

</script>