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JavaScript HTML DOM Navigation
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With the HTML DOM, you can navigate the node tree using node relationships.

DOM Nodes
According to the W3C HTML DOM standard, everything in an HTML document is a node:

The entire document is a document node
Every HTML element is an element node
The text inside HTML elements are text nodes
Every HTML attribute is an attribute node
All comments are comment nodes
With the HTML DOM, all nodes in the node tree can be accessed by JavaScript.

New nodes can be created, and all nodes can be modified or deleted.

Node Relationships
The nodes in the node tree have a hierarchical relationship to each other.

The terms parent, child, and sibling are used to describe the relationships.

In a node tree, the top node is called the root (or root node)
Every node has exactly one parent, except the root (which has no parent)
A node can have a number of children
Siblings (brothers or sisters) are nodes with the same parent

 
      DOM Tutorial
 

 
     

DOM Lesson one

     

Hello world!

 

From the HTML above you can read:

is the root node
has no parents
is the parent of and
is the first child of
is the last child of
and:

has one child:
has one child (a text node): “DOM Tutorial”
has two children:

and

has one child: “DOM Lesson one”

has one child: “Hello world!”

and

are siblings
Navigating Between Nodes
You can use the following node properties to navigate between nodes with JavaScript:

parentNode
childNodes[nodenumber]
firstChild
lastChild
nextSibling
previousSibling
Child Nodes and Node Values
A common error in DOM processing is to expect an element node to contain text.

Example:
DOM Tutorial
The element node (in the example above) does not contain text.

It contains a text node with the value “DOM Tutorial”.

The value of the text node can be accessed by the node’s innerHTML  property:

var myTitle = document.getElementById(“demo”).innerHTML;
Accessing the innerHTML property is the same as accessing the nodeValue of the first child:

var myTitle = document.getElementById(“demo”).firstChild.nodeValue;
Accessing the first child can also be done like this:

var myTitle = document.getElementById(“demo”).childNodes[0].nodeValue;
All the (3) following examples retrieves the text of an

element and copies it into a

element:

Example

My First Page

document.getElementById(“id02”).innerHTML = document.getElementById(“id01”).innerHTML;

»
Example

My First Page

document.getElementById(“id02”).innerHTML = document.getElementById(“id01”).firstChild.nodeValue;

»
Example

My First Page

Hello!

document.getElementById(“id02”).innerHTML = document.getElementById(“id01”).childNodes[0].nodeValue;

»
InnerHTML
In this tutorial we use the innerHTML property to retrieve the content of an HTML element.

However, learning the other methods above is useful for understanding the tree structure and the navigation of the DOM.

DOM Root Nodes
There are two special properties that allow access to the full document:

document.body – The body of the document
document.documentElement – The full document
Example

Hello World!

alert(document.body.innerHTML);

»
Example

Hello World!

alert(document.documentElement.innerHTML);

»
The nodeName Property
The nodeName property specifies the name of a node.

nodeName is read-only
nodeName of an element node is the same as the tag name
nodeName of an attribute node is the attribute name
nodeName of a text node is always #text
nodeName of the document node is always #document
Example

My First Page

document.getElementById(“id02”).innerHTML = document.getElementById(“id01”).nodeName;

»
Note: nodeName always contains the uppercase tag name of an HTML element.

The nodeValue Property
The nodeValue property specifies the value of a node.

nodeValue for element nodes is undefined
nodeValue for text nodes is the text itself
nodeValue for attribute nodes is the attribute value
The nodeType Property
The nodeType property returns the type of node. nodeType is read only.

Example

My First Page

document.getElementById(“id02”).innerHTML = document.getElementById(“id01”).nodeType;

»
The most important node types are:

Element type NodeType
Element 1
Attribute 2
Text 3
Comment 8
Document 9

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