Tutorials » XML and Javascript

Introduction:

XML is a very important base on which Web Services work. XML can be used in conjunction with a lot of client side and server side languages to put it to good effect. Let us see how we can use XML and client side JavaScript to work. We will see how we can display the contents of a XML file using JavaScript, accessing child elements, manipulating elements etc.

Browser Issues:

When it comes client side languages browser incompatibilities is a major issue. But here where we want to use XML and JavaScript, XML is the issue. Not all browsers have support for parsing XML documents. I will use IE6 to explain the codes. Browsers that do not support XML, cannot read them. When you view an XML file in such a browser it will just ignore all the tags.

Sample XML file:

<company>
<employee id="001" sex="M" age="19">Premshree Pillai</employee>
<employee id="002" sex="M" age="24">Kumar Singh</employee>
<employee id="003" sex="M" age="21">Ranjit Kapoor</employee>
<turnover>
<year id="2000">100,000</year>
<year id="2001">140,000</year>
<year id="2002">200,000</year>
</turnover>
</company>

The above XML file shows employee data and Turnover of the company (just an e.g).

Manipulating XML file data using JavaScript:

Loading XML file data using Javascript
    var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");
    function loadXML(xmlFile)
    {
        xmlDoc.async="false";
        xmlDoc.onreadystatechange=verify;
        xmlDoc.load(xmlFile);
        xmlObj=xmlDoc.documentElement;
    }

    Actually, just the last two lines of the function are enough to load the XML file. The     previous two lines are written to ensure that the JavaScript functions that we may     use later to manipulate the XML file data, does not perform any function on an     uninitialized object. Thus the function verify()is called.

    function verify()
    {
        // 0 Object is not initialized
        // 1 Loading object is loading data
        // 2 Loaded object has loaded data
        // 3 Data from object can be worked with
        // 4 Object completely initialized
        if (xmlDoc.readyState != 4)
        {
            return false;
        }
    }

    Now the XML file can be loaded

         loadXML('xml_file.xml');
Displaying contents of XML file: View the entire contents of the XML file using alert(xmlObj.xml); The entire XML file will be displayed in an alert box as it is with proper indentation.

Children and nodes: In the above XML file <company> is the top level tag under which all other tags come. These tags are called children. The above XML file can be represented graphically like a folder-tree. A folder-tree is shown below.

Thus in the above XML file the top level tag <company> has 4 children.The numbering of children (as is usual in all languages) starts from 0 (zero).The <turnover> tag has 3 children under it.

We can find the no of children a tag has by using the childNodes.length property. Thus the no of childen of <company> tag (here, 4) can be found by using xmlObj.childNodes.length

The no of children of <turnover> tag (here, 3) can be found by using xmlObj.childNodes(3).childNodes.length

Here we use childNodes(3) because <turnover> is the 3rd child of <company>

Testing for children: You can test whether a particular node child has any children using childNodes(i).hasChildNodes. Thus mlObj.childNodes(3).hasChildNodes() will return true.

Getting Tag Name: You can get the tag name of a child using
    childNodes(i).tagName. Thus xmlObj.tagName will return "company".
    xmlObj.childNodes(0).tagName will return "employee".
    xmlObj.childNodes(3).childNodes(0).tagName will return "year".

Displaying content of a tag: In the XML file the content of the 1st <employee> tag is "Premshree Pillai". You can get this value using xmlObj.childNodes (0).firstChild.text xmlObj.childNodes(2).firstChild.text will return "Suhasini Pandita". Similarly xmlObj.childNodes(3).childNodes(1).firstChild.text will return "140,000".

Attributes : In the XML file, the <employee> tag has 3 attributes. An attribute can be     accessed using childNodes(i).getAttribute("AttributeName"). Thus     xmlObj.childNodes(0).getAttribute("id") will return "001".
    xmlObj.childNodes(1).getAttribute("age") will return "24".
    xmlObj.childNodes(2).getAttribute("sex") will return "F".

XML - JavaScript Example: There are many more properties and methods available. Using these properties you can create lots of client side applications. The main advantage of using XML along with JavaScript is that editing of data becomes very easy. XML being structured, it becomes very easy to manage content. One example is a folder-tree menu. Another one is a JavaScript Ticker. You can find a XML based JavaScript Ticker at

http://www.dynamicdrive.com/dynamicindex2/xmlticker.htm

XML based JavaScript Ticker :
We will create a XML based JavaScript Ticker that can tick any number of messages. The ticker reads it's contents, i.e the ticker style, text to be displayed, the link for that particular message from a XML file. Let the XML file be ticker_items.xml

The structure of the XML document is as follows >>

TICKER
tickerstyle
  >>pause = "true" / "false" :: "true" for pause onMouseOver
  >>timeout = any integer :: The delay in seconds between different messages.
  >>border = any integer :: Border width of Ticker
  >>bordercolor = #HexColor :: The border color of Ticker
  >>background = #HexColor :: Background color of Ticker
  >>width = any integer :: Ticker width
  >>height = any integer :: Ticker height
tickerlinkstyle
  mouseout
    >>font = "verdana,arial,helvetica....." :: Ticker link font
    >>color = #HexColor :: Ticker link color
    >>decoration = "none" / "underline" / "underline + overline" :: Ticker link style
    >> weight = "normal" / "bold" :: Ticker link weight
    >>size = 'any integer'pt :: Ticker link size
  mouseover
    >>font = "verdana,arial,helvetica....." :: Ticker link font
    >>color = #HexColor :: Ticker link color
    >>decoration = "none" / "underline" / "underline + overline" :: Ticker link style
    >>weight = "normal" / "bold" :: Ticker link weight
    >>size = 'any integer'pt :: Ticker link size
tickeritem
    >>URL = A valid URL :: Ticker link URL
    >>target = "_blank" / "_top" / "_self" / 'any other valid target name' :: Ticker link         target

This is the script Script

As you can see in the source code, the ticker reads all the contents/messages to be displayed, the links for each message, the target for each URL, the ticker static style, roll-over style, border width, color, background, the delay between messages etc from the XML file. So if you want to change any parameter of the Ticker, all you have to do is make necessary changes in the XML file.

The ticker shown here is a basic ticker that rotates messages at an interval that is specified in the XML file. There are many effects you could add to the ticker like 'Fading message', 'Teletypewriter'. You could add features to change the ticker speed or to list all messages at an instant.

I hope this article has helped you in some way.

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Tutorials » XML and Javascript