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XML DOM - Navigating Nodes

Nodes can be navigated using node relationships.

Examples

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

Get the parent of a node
This example uses the parentNode property to get the parent of a node

Get the first child element of a node
This example uses the firstChild() method and a custom function to get the first child node of a node

Navigating DOM Nodes

Accessing nodes in the node tree via the relationship between nodes, is often called "navigating nodes".

In the XML DOM, node relationships are defined as properties to the nodes:

parentNode
childNodes
firstChild
lastChild
nextSibling
previousSibling

The following image illustrates a part of the node tree and the relationship between nodes in books.xml:

Node tree

DOM - Parent Node

All nodes has exactly one parent node. The following code navigates to the parent node of <book>:

xmlDoc=loadXMLDoc("books.xml");

x=xmlDoc.getElementsByTagName("book")[0];
document.write(x.parentNode.nodeName);

Example explained:

Load "books.xml" into xmlDoc using loadXMLDoc()
Get the first <book> element
Output the node name of the parent node of "x"

Try it yourself

Avoid Empty Text Nodes

Firefox, and some other browsers, will treat empty white-spaces or new lines as text nodes, Internet Explorer will not.

This causes a problem when using the properties: firstChild, lastChild, nextSibling, previousSibling.

To avoid navigating to empty text nodes (spaces and new-line characters between element nodes), we use a function that checks the node type:

function get_nextSibling(n)
{
y=n.nextSibling;
while (y.nodeType!=1)
  {
  y=y.nextSibling;
  }
return y;
}

The function above allows you to use get_nextSibling(node) instead of the property node.nextSibling.

Code explained:

Element nodes are type 1. If the sibling node is not an element node, it moves to the next nodes until an element node is found. This way, the result will be the same in both Internet Explorer and Firefox.

Get the First Child Element

The following code displays the first element node of the first <book>:

<html>
<head>
<script type="text/javascript" src="loadxmldoc.js">
</script>
<script type="text/javascript">
//check if the first node is an element node
function get_firstChild(n)
{
y=n.firstChild;
while (y.nodeType!=1)
  {
  y=y.nextSibling;
  }
return y;
}
</script>
</head>

<body>
<script type="text/javascript">
xmlDoc=loadXMLDoc("books.xml");

x=get_firstChild(xmlDoc.getElementsByTagName("book")[0]);
document.write(x.nodeName);
</script>
</body>
</html>

Output:

title

Example explained:

Load "books.xml" into xmlDoc using loadXMLDoc()
Use the get_firstChild fucntion on the first <book> element node to get the first child node that is an element node
Output the node name of first child node that is an element node

Try it yourself

Examples

The following examples use a similar function:

firstChild: Try it yourself lastChild: Try it yourself

nextSibling: Try it yourself previousSibling: Try it yourself