javascript

Chapter 15: XML in JavaScript
To create a new XML document with document element of < root > , the following code can be used:
var xmldom = document.implementation.createDocument(“”, “root”, null);
alert(xmldom.documentElement.tagName); //”root”
var child = xmldom.createElement(“child”);
xmldom.documentElement.appendChild(child);
This example creates an XML DOM document with no default namespace and no doctype . Note that
even though a namespace and doctype aren ’ t needed, the arguments must still be passed in. An empty
string is passed as the namespace URI so that no namespace is applied, and null is passed as the
doctype. The xmldom variable contains an instance of the DOM Level 2 Document type, complete with
all of the DOM methods and properties discussed in Chapter 11 . In this example, the document
element ’ s tag name is displayed and then a new child element is created and added.
You can check to see if DOM Level 2 XML support is enabled in a browser by using the following line of
code:
var hasXmlDom = document.implementation.hasFeature(“XML”, “2.0”);
In practice, it is rare to create an XML document from scratch and then build it up systematically using
DOM methods. It is much more likely that an XML document needs to be parsed into a DOM structure
or vice versa. Because DOM Level 2 didn ’ t provide for such functionality, a couple of de facto standards
emerged.
The DOM Parser Type
Firefox introduced the DOMParser type specifically for parsing XML into a DOM document, and it was
later adopted by Opera. To use it, you must first create an instance of DOMParser and then call the
parseFromString() method. This method accepts two arguments: the XML string to parse and a
content type, which should always be “ text/xml ” . The return value is an instance of Document .
Consider the following example:
var parser = new DOMParser();
var xmldom = parser.parseFromString(“ < root > < child/ > < /root > ”, “text/xml”);
alert(xmldom.documentElement.tagName); //”root”
alert(xmldom.documentElement.firstChild.tagName); //”child”
var anotherChild = xmldom.createElement(“child”);
xmldom.documentElement.appendChild(anotherChild);
var children = xmldom.getElementsByTagName(“child”);
alert(children.length); //2
In this example, a simple XML string is parsed into a DOM document. The DOM structure has < root >
as the document element with a single < child > element as its child. You can then interact with the
returned document using DOM methods.
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