XML DOM Access Nodes

With the DOM, you can access every node in an XML document.

Find and Access Nodes

You can find the element you want to manipulate in several ways:

• By using the getElementsByTagName() method
• By using the parentNode, firstChild, and lastChild properties of an element node

getElementsByTagName()

The getElementsByTagName() method can find any XML element in the entire document.

This method ignore the document structure. If you want to find all <book> elements in the document, the getElementsByTagName() method will find them all, regardless of on which level the <book> elements are.

This method gives you the XML elements you need regardless of where they are in the document!

The getElementsByTagName() method returns all elements (as a nodeList) with the specified tag name that are descendants of the element you are on when using this method.

The getElementsByTagName() can be used on any XML element:

getElementsByTagName() Syntax

getElementsByTagName("tagname");

Example

The following example returns a nodeList of all <book> elements in the document:

xmlDoc.getElementsByTagName("book");

nodeList

When working with a nodeList, we usually store the list in a variable, like this:

var x=xmlDoc.getElementsByTagName("book");

Now the variable x contains a list of all <book> elements in the page, and we can access the <book> elements by their index numbers.

Note: The index starts at 0.

You can loop through the nodeList by using the length property:

var x=xmlDoc.getElementsByTagName("book");
for (var i=0;i<x.length;i++)
  { 
  // do something with each <book> element
  }

You can also access a specific element by using the index number.

To access the third <p> you can write:

var y=x[2];

parentNode, firstChild, and lastChild

The five properties parentNode, firstChild, and lastChild follow the document structure and allow short-distance travel in the document.

Look at the following XML fragment:

<bookstore>
  <book category="COOKING">
    <title lang="en">Everyday Italian</title> 
    <author>Giada De Laurentiis</author> 
    <year>2005</year> 
    <price>30.00</price> 
  </book>
</bookstore>

In the HTML code above, the <title> element is the firstChild of the <book> element, and the <price> element is the lastChild of the <book> element.

Furthermore, the <book> element is the parentNode of the <title>, <author>, <year>, and <price> elements.

Root Nodes

There is one special document property that allow access to the tags:

• document.documentElement

This property returns the root node of the document and exists in all XML and HTML documents.

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