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XML DOM - Node List and NamedNodeMap

From http://www.w3schools.com (Copyright Refsnes Data)

XML DOM Node List

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A list of nodes is returned by the getElementsByTagName() method and the childNodes property.


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 text from the first <title> element
This example uses the getElementsByTagName() method to get the text from the first <title> element in "books.xml".

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

Get the attribute of an element
This example uses a attribute list to get attribute from the first <book> element in "books.xml".


DOM Node List

When using properties or methods like childNodes or getElementsByTagName(), a node list object is returned.

A node list object represents a list of nodes, in the same order as in the XML.

Nodes in the node list are accessed with index numbers starting from 0.

The following image represents a node list of the <title> elements in "books.xml":

DOM node list

The following code fragment loads "books.xml" into xmlDoc using loadXMLDoc() and returns a node list of title elements in "books.xml":

xmlDoc=loadXMLDoc("books.xml");
x=xmlDoc.getElementsByTagName("title");

After the execution of the statement above, x is a node list object.

The following code fragment returns the text from the first <title> element in the node list (x):

txt=x[0].childNodes[0].nodeValue;

After the execution of the statement above, txt = "Everyday Italian".

Try it yourself.


Node List Length

A node list object keeps itself up-to-date. If an element is deleted or added, the list is automatically updated.

The length property of a node list is the number of nodes in the list.

The following code fragment loads "books.xml" into xmlDoc using loadXMLDoc() and returns the number of <title> elements in "books.xml":

xmlDoc=loadXMLDoc("books.xml");
x=xmlDoc.getElementsByTagName('title').length;

After the execution of the statement above, x = 4.

The length of the node list can be used to loop through all the elements in the list.

The following code fragment uses the length property to loop through the list of <title> elements:

xmlDoc=loadXMLDoc("books.xml");
//the x variable will hold a node list
x=xmlDoc.getElementsByTagName('title');
for (i=0;i<x.length;i++)
{
document.write(x[i].childNodes[0].nodeValue);
document.write("<br />");
}

Output:

Everyday Italian
Harry Potter
XQuery Kick Start
Learning XML

Example explained:

  1. Load "books.xml" into xmlDoc using loadXMLDoc()
  2. Set the x variable to hold a node list of all title elements
  3. Output the value from the text node of all <title> elements

Try it yourself.


DOM Attribute List (Named Node Map)

The attributes property of an element node returns a list of attribute nodes.

This is called a named node map, and is similar to a node list, except for some differences in methods and properties.

A attribute list keeps itself up-to-date. If an attribute is deleted or added, the list is automatically updated.

The following code fragment loads "books.xml" into xmlDoc using loadXMLDoc() and returns a list of attribute nodes from the first <book> element in "books.xml":

xmlDoc=loadXMLDoc("books.xml");
x=xmlDoc.getElementsByTagName('book')[0].attributes;

After the execution of the code above, x.length = is the number of attributes and x.getNamedItem() can be used to return an attribute node.

The following code fragment displays the value of the "category" attribute, and the number of attributes, of a book:

xmlDoc=loadXMLDoc("books.xml");
x=xmlDoc.getElementsByTagName("book")[0].attributes;
document.write(x.getNamedItem("category").nodeValue);
document.write("<br />" + x.length);

Output:

cooking
1

Example explained:

  1. Load "books.xml" into xmlDoc using loadXMLDoc()
  2. Set the x variable to hold a list of all attributes of the first <book> element
  3. Output the value from the "category" attribute
  4. Output the length of the attribute list

Try it yourself.


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From http://www.w3schools.com (Copyright Refsnes Data)

Home>Manual>XML DOM - Node List and NamedNodeMap