Chapter 8 Working with XML Documents

Working with elements

Many applications that process XML documents need to locate or manipulate various elements of the document by using the tree structure.

The DOM interface provides two objects for working with elements:

DOMNode object You can use the DOMNode object and test to see if the node you are addressing is an element node.
DOMElement object You can explicitly use the DOMElement object, which provides some additional properties and methods that reflect the features of XML elements.

Using the DOMNode object to work with elements

The element nodes of a document have all the properties (parents, siblings, children) that you need to navigate a document. These nodes provide one way to access the properties of elements.

Example

Here is a script that writes out the names of all elements in a document:

function displayElementName( domElement ){           //1
  var i;                                             //2
  var domChild;                                      //3
  if( domElement.nodeType == 1){                     //4
      document.writeln( domElement.nodeName );       //5
  }                                                  //6 
  for( i=0; i < domElement.childNodes.length ; i++ ){//7
    domChild = domElement.childNodes.item(i);        //8
    displayElementName( domChild );                  //9
  }                                                 //10
}                                                   //11
displayElementName( domDoc.documentElement );       //12

Notes

Lines 2 and 3 When calling a function recursively, as in this example, you must declare variables inside the function to ensure a new copy is made each time.
Lines 4 to 6 Only write out the names of nodes that are elements (nodeType = 1).
Lines 7 to 10 Loop over all the child nodes of the current node, calling displayElementName on each.
Line 12 Invoke displayElementName with the document element of a DOM document. The function must be defined before it is used.

Characteristics of nodes that represent elements

Nodes that correspond to elements have the following characteristics:

nodeType The nodeType of a node that is an element is 1.
nodeName This is the tag name of the element.
nodeValue The nodeValue of a node that is an element is null.
attributes The attributes of an element. These are made available as a DOMNamedNodeMap object.

For more information about attributes, see "Working with attributes".

Using the DOMElement object to work with elements

The DOMElement object corresponds to an element of an XML document. DOMElement inherits all the properties and methods from the DOMNode object. In addition, it supports some properties and methods specific to elements.

You can retrieve and process all elements with a given name from a document as follows:

elemlist = domObj.getElementsByTagName(tag_name);
for(i=0; i < elemlist.length ; i++){
  document.writeln( elemlist.item(i).tagName);
}

where domObj is a DOMDocument object or a DOMElement object, and tag_name is the case-sensitive name of the tag you want to retrieve. If domObj is a DOMElement object, only those elements contained in domObj are retrieved (descendants of domObj ).

This is usually more effective than traversing the entire document tree looking for a particular element.

For a list of DOMElement properties and methods, see "The DOMElement object" in the PowerDynamo Reference Manual.