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BOOK: Professional JavaScript for Web Developers 2nd edition ISBN: 9780470227800
This is the forum to discuss the Wrox book Professional JavaScript for Web Developers, 2nd Edition by Nicholas C Zakas; ISBN: 9780470227800
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Old December 9th, 2009, 07:06 PM
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Default Javascript and XPath when XPathEvaluator fails...

Working through the Javascript book "Professional Javascript for Web Developers" by Wrox, author "Zakas".
In particular I am working through his section on how to handle XML processing in Javascript.

What I am trying to ascertain is:
His section on dealing with XPath notes that there are some browsers that won't work with the XPathEvaluator.
He states that I should use the "corresponding methods on the Document" to make up for the short coming in
some browsers. Could someone give me an idea on what he means by "corresponding methods on the Document"?

His crossbrowser functions for Xpath:

Code:
 
// { prefix1: 'uri1', prefix2: 'uri2' } //example of namespace object
}
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"):
    }
}// end function selectSingleNode()
 
var result = selectSingleNode(xmldom.documentElement, "wrox:book/wrox:author", {wrox: "http://www.wrox.com/" });
// result is an object
 
//using the same namespaces literal above...
 
function selectNodes(context, expression, namespaces){ //selecting multiple nodes in a crossbrowser fashion
        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_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.slectNodes != "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.lenght; i<len; i++){
            nodes.push(result[i]);
        }
        
        return nodes;
        
    } else {
        
        throw new Error("no xpath engine");
        
    }
    
}// end function selectNodes();
 
//function call
var result = selectNodes(xmldom.documentElement, "wrox:book/wrox:author", { wrox: "http://www.wrox.com/" });
thanx kevin
 
Old December 9th, 2009, 09:56 PM
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Default

Internet Explorer is the only browser that now doesn't support XPathEvaluator. You can use selectNode() and selectSingleNode() on the DOM Document object instead (IE only).
__________________
Nicholas C. Zakas
Author, Professional JavaScript for Web Developers (ISBN 0764579088)
http://www.nczonline.net/
 
Old December 10th, 2009, 04:23 PM
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Default

thanx
great book

Kevin




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