XML DOM Access Nodes

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

Accessing Nodes

You can access a node in three ways:

  • By using the getElementsByTagName() method
  • By looping through (traversing) the nodes tree
  • 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.

    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];
    Note: The index starts at 0.

    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:

    Example

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

    for (i = 0; i <x.length; i++) {
      // do something for each node
      }

    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.

    Traversing Nodes

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

    Example

    txt = "";
    x = xmlDoc.documentElement.childNodes;

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

    Example explained:

    Navigating Node Relationships

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

    Example

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

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

    Example explained: