JavaScript Remote Scripting: Processing XML Files

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JavaScript Remote Scripting:Processing XML Files
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In this article, you will learn how to use AJAX forreading and manipulating simple XML files, in order to implement abasic Web service. Specifically, you will learn how to develop aJavaScript application that fetches data from an XML file. By the endof this article, you will know the basics for using client-side parsedXML in your own applications.Here you have it. Welcome to thesecond part of the series “JavaScript Remote Scripting.” Based on thetheoretical concepts explained in the first tutorial, as well as theirapplication in an illustrative example, I’ve demonstrated how to readfile data from the server by using AJAX as the primary method formaking http requests in the background, without having to reload thecurrent page.
Stepping back for a moment to the scriptthat I previously developed in the first article, it implements asimple mechanism for fetching data from a plain text file anddisplaying the information through a predefined sequence. Although theexample is rather basic, it does exposes the foundations of AJAXtechnology for building more complex and polished applications, byutilizing as core programming logic the powerful capabilities forsending silent http requests on the fly.
The best thingwith this approach is that it offers a broad range of applications forfetching data from the server in multiple formats. Of course you havealready seen how easy it is to fetch data from flat text files anddisplay their contents directly on the browser, all without messing upthings too much with complex server-side programs. Moreover, AJAX comeswith native support for pulling out data served as XML, by using the“responseXML” property that belongs to the XMLHtttpRequest object.
Consideringthat XML is today one of the most common data carriers used whenworking with Web services, this second part of the series will putstrong attention to developing a JavaScript application that fetchesdata from an XML file, by taking advantage of the native capabilitiesthat AJAX brings to developers for working with this markup language.In my attempt to illustrate the relevant role of AJAX within the areaof remote scripting, by the end of this article you will know thebasics for using client-side parsed XML in your own applications.
Nowthat you know the objectives of this second part of the series, it’stime to move on to learn more about JavaScript-based XML processing.Let’s get going!
JavaScript Remote Scripting:Processing XML Files - XML in the client: the basics of AJAX XML processing
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Inaddition to the “responseText” property that you saw in the firstarticle, the XMLHttpRequest object offers the “responseXML” property,useful for processingserverresponse, which has been sent back to the client as XML data. Usingregular DOM methods, it’s possible to parse basically XML in the clientand implement some kind of interaction, either for boosting thecapabilities of user interfaces or the application layer itself.
Withreference to the above deployed concepts, in conjunction with thesample news rotator that I developed in part one of this series, whatI’ll do next is write a simple script that retrieves some headlinesfrom a XML file, then processes them and finally displays the resultsdirectly on the browser. Considering that client-side flat text fileprocessing has already been covered, the next example will illustratehow to parse XML files once the corresponding http request has beensuccessfully completed.
As you might guess, in order toget the script parsing XML, first I’ll need to work with sample dataserved as XML. In this particular case, I’ll define a simple XML file,which contains some headlines to be included in the news rotator. Itsdefinition is the following:




http://www.devarticles.com



http://www.php.net



http://www.google.com/apis/maps/documentation/



http://www.mysql.com



http://www.macromedia.com



http://www.php.net


Asyou can see, the above listed XML file presents a simple structure fordefining the appropriate headlines to be displayed, as well as the URLstied to them. With reference to the document hierarchy, I’ve defined ageneral tag, which is placed on top of the document tree,and then created a few nodes to wrap up both






To wrap up
That’sit for now. Throughout this second part of the series, you’ve hopefullylearned how to use AJAX for reading and manipulating simple XML files,in order to implement a basic Web service. Certainly, the concepts thatI illustrated at the very beginning imply a challenge for developingricher applications that use remote scripting to provide users with amore interactive experience.
The third tutorial of theseries goes one step further with remote scripting, by explaining itsimplementation through the use of fully-standard DOM methods, withoutgetting a single foot into AJAX technology. Want to know more? Justwait for the next part!
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