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XML DOM: Navigating Nodes

Nodes can be navigated using node relationships.

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

DOM: Parent Node​

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

function myFunction(xml) {  
	var xmlDoc = xml.responseXML;  
	var x = xmlDoc.getElementsByTagName("book")[0];  
	document.getElementById("demo").innerHTML = x.parentNode.nodeName;  
}

Explanation:

  1. Load books.xml into xmlDoc
  2. Get the first <book> element
  3. Output the node name of the parent node of "x"

Avoid Empty Text Nodes​

Some browsers might treat empty white-spaces or new lines as text nodes. 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)  {  
	var 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.

Get the First Child Element​

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

<!DOCTYPE html>
<html>
    <body>
        <p id="demo"></p>
        <script>
            var xhttp = new XMLHttpRequest();
            xhttp.onreadystatechange = function() {
                if (this.readyState == 4 && this.status == 200) {
                    myFunction(this);
                }
            };
            xhttp.open("GET", "books.xml", true);
            xhttp.send();
            
            function myFunction(xml) {
                var xmlDoc = xml.responseXML;
                var x = get_firstChild(xmlDoc.getElementsByTagName("book")[0]);
                document.getElementById("demo").innerHTML = x.nodeName;
            }
            
            //check if the first node is an element node
            function get_firstChild(n) {
                var y = n.firstChild;
                while (y.nodeType != 1) {
                    y = y.nextSibling;
                }
                return y;
            }
        </script>
    </body>
</html>

Explanation:

  1. Load books.xml nto xmlDoc
  2. Use the get_firstChild function on the first <book> element node to get the first child node that is an element node
  3. Output the node name of first child node that is an element node

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