XML DOM - Accessing Nodes

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

Examples

The examples below use the XML file books.xml.
A function, loadXMLDoc(), in an external JavaScript is used to load the XML file.

Access a node using its index number in a node list
This example uses the getElementsByTagname() method to get the third <title> element in "books.xml"

Loop through nodes using the length property
This example uses the length property to loop through all <title> elements in "books.xml"

See the node type of an element
This example uses the nodeType property to get node type of the root element in "books.xml".

Loop through element nodes
This example uses the nodeType property to only process element nodes in "books.xml".

Loop through element nodes using node realtionships
This example uses the nodeType property and the nextSibling property to process element nodes in "books.xml".

Accessing Nodes

You can access a node in three ways:

1. By using the getElementsByTagName() method

2. By looping through (traversing) the nodes tree.

3. By navigating the node tree, using the node relationships.

The getElementsByTagName() Method

getElementsByTagName() returns all elements with a specified tag name.

Syntax

node.getElementsByTagName("tagname");

Example

The following example returns all <title> elements under the x element:

x.getElementsByTagName("title");

Note that the example above only returns <title> elements under the x node. To return all <title> elements in the XML document use:

xmlDoc.getElementsByTagName("title");

where xmlDoc is the document itself (document node).

DOM Node List

The getElementsByTagName() method returns a node list. A node list is an array of nodes.

The following code loads "books.xml" into xmlDoc using loadXMLDoc() and stores a list of <title> nodes (a node list) in the variable x:

xmlDoc=loadXMLDoc("books.xml");

x=xmlDoc.getElementsByTagName("title");

The <title> elements in x can be accessed by index number. To access the third <title> you can write:

y=x[2];

Try it yourself.

Note: The index starts at 0.

You will learn more about node lists in a later chapter of this tutorial.

DOM Node List Length

The length property defines the length of a node list (the number of nodes).

You can loop through a node list by using the length property:

xmlDoc=loadXMLDoc("books.xml");

x=xmlDoc.getElementsByTagName("title");

for (i=0;i<x.length;i++)
  { 
  document.write(x[i].childNodes[0].nodeValue);
  document.write("<br />");
  }

Example explained:

1. Load "books.xml" into xmlDoc using loadXMLDoc()
2. Get all <title> element nodes
3. For each title element, output the value of its text node

Try it yourself.

Node Types

The documentElement property of the XML document is the root node.

The nodeName property of a node is the name of the node.

The nodeType property of a node is the type of the node.

You will learn more about the node properties in the next chapter of this tutorial.

Try it yourself.

Traversing Nodes

The following code loops through the child nodes, that are also element nodes, of the root node:

xmlDoc=loadXMLDoc("books.xml");

x=xmlDoc.documentElement.childNodes;

for (i=0;i<x.length;i++)
{ 
  if (x[i].nodeType==1)
  {//Process only element nodes (type 1) 
  document.write(x[i].nodeName);
  document.write("<br />");
  } 
}

Example explained:

1. Load "books.xml" into xmlDoc using loadXMLDoc()
2. Get the child nodes of the root element
3. For each child node, check the node type of the node. If the node type is "1" it is an element node
4. Output the name of the node if it is an element node

Try it yourself.

Navigating Node Relationships

The following code navigates the node tree using the node relationships:

xmlDoc=loadXMLDoc("books.xml");

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

for (i=0;i<x.length;i++)
{
if (y.nodeType==1)
  {//Process only element nodes (type 1)
  document.write(y.nodeName + "<br />");
  }
y=y.nextSibling;
}

1. Load "books.xml" into xmlDoc using loadXMLDoc()
2. Get the child nodes of the first book element
3. Set the "y" variable to be the first child node of the first book element
4. For each child node (starting with the first child node "y"):
5. Check the node type. If the node type is "1" it is an element node
6. Output the name of the node if it is an element node
7. Set the "y" variable to be the next sibling node, and run through the loop again

Try it yourself.