XML DOM Advanced

The XML DOM (Document Object Model) defines a standard way for accessing and manipulating XML documents.

The XML DOM

The DOM views XML documents as a tree-structure. All elements can be accessed through the DOM tree. Their content (text and attributes) can be modified or deleted, and new elements can be created. The elements, their text, and their attributes are all known as nodes.

In an earlier chapter of this tutorial we introduced the XML DOM , and used the XML DOM getElementsByTagName() method to retrieve data from a DOM tree.

In this chapter we will describe some other commonly used XML DOM methods. In the examples, we have used the XML file books.xml, and a JavaScript function to load the XML file into an DOM object called xmlDoc.

To learn all about the XML DOM, please visit our XML DOM tutorial.

Get the Value of an Element

The following code retrieves the text value of the first <title> element:

x=xmlDoc.getElementsByTagName("title")[0].childNodes[0];
txt=x.nodeValue;

Result:  txt = "Everyday Italian"

Try it yourself

Get the Value of an Attribute

The following code retrieves the text value of the "lang" attribute of the first <title> element:

txt=xmlDoc.getElementsByTagName("title")[0].getAttribute("lang");

Result:  txt = "en"

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Change the Value of an Element

The following code changes the text value of the first <title> element:

x=xmlDoc.getElementsByTagName("title")[0].childNodes[0];
x.nodeValue="Easy Cooking";

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Change the Value of an Attribute

The setAttribute() method can be used to change the value of an existing attribute, or to create a new attribute.

The following code adds a new attribute called "edition" (with the value "first") to each <book> element:

x=xmlDoc.getElementsByTagName("book");

for(i=0;i<x.length;i++)
  {
  x[i].setAttribute("edition","first");
  }

Try it yourself

Create an Element

The createElement() method creates a new element node.

The createTextNode() method creates a new text node.

The appendChild() method adds a child node to a node (after the last child).

To create a new element with text content, it is necessary to create both an element node and a text node.

The following code creates an element (<edition>), and adds it to the first <book> element:

newel=xmlDoc.createElement("edition");
newtext=xmlDoc.createTextNode("First");
newel.appendChild(newtext);

x=xmlDoc.getElementsByTagName("book");
x[0].appendChild(newel);

Example explained:

• Create an <edition> element
• Create a text node with value = "First"
• Append the text node to the <edition> element
• Append the <edition> element to the first <book> element

Try it yourself

Remove an Element

The removeChild() method removes a specified node (or element).

The following code fragment will remove the first node in the first <book> element:

x=xmlDoc.getElementsByTagName("book")[0];

x.removeChild(x.childNodes[0]);

Try it yourself

Note: The result of the example above may be different depending on what browser you use. Firefox treats new lines as empty text nodes, Internet Explorer don't. You can read more about this and how to avoid it in the XML DOM tutorial.

These were a few examples of things you can do with the XML DOM.

To learn all about the XML DOM, please visit our XML DOM tutorial.

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