JavaScript HTML DOM Navigation
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
<html>
<head>
<title>DOM Tutorial</title>
</head>
<body>
<h1>DOM Lesson one</h1>
<p>Hello world!</p>
</body>
</html>
From
the HTML above you can read:
<html>
is the root node
<html>
has no parents
<html>
is the parent of <head> and <body>
<head>
is the first child of <html>
<body>
is the last child of <html>
and:
<head>
has one child: <title>
<title>
has one child (a text node): "DOM Tutorial"
<body>
has two children: <h1> and <p>
<h1>
has one child: "DOM Lesson one"
<p>
has one child: "Hello world!"
<h1>
and <p> 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:
<title
id="demo">DOM Tutorial</title>
The element
node <title> (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 <h1> element and copies it
into a <p> element:
Example
<html>
<body>
<h1
id="id01">My First Page</h1>
<p
id="id02"></p>
<script>
document.getElementById("id02").innerHTML
= document.getElementById("id01").innerHTML;
</script>
</body>
</html>
»
Example
<html>
<body>
<h1
id="id01">My First Page</h1>
<p
id="id02"></p>
<script>
document.getElementById("id02").innerHTML
= document.getElementById("id01").firstChild.nodeValue;
</script>
</body>
</html>
»
Example
<html>
<body>
<h1
id="id01">My First Page</h1>
<p
id="id02">Hello!</p>
<script>
document.getElementById("id02").innerHTML
= document.getElementById("id01").childNodes[0].nodeValue;
</script>
</body>
</html>
»
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
dy.innerHTML);
</script>
</body>
</html>
»<html>
<body>
<p>Hello
World!</p>
<div>
<p>The
DOM is very useful!</p>
<p>This
example demonstrates the <b>document.body</b> property.</p>
</div>
<script>
alert(document.bo
Example
<html>
<body>
<p>Hello
World!</p>
<div>
<p>The
DOM is very useful!</p>
<p>This
example demonstrates the <b>document.documentElement</b>
property.</p>
</div>
<script>
alert(document.documentElement.innerHTML);
</script>
</body>
</html>
»
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
<h1
id="id01">My First Page</h1>
<p
id="id02"></p>
<script>
document.getElementById("id02").innerHTML
= document.getElementById("id01").nodeName;
</script>
»
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
<h1
id="id01">My First Page</h1>
<p
id="id02"></p>
<script>
document.getElementById("id02").innerHTML
= document.getElementById("id01").nodeType;
</script>
»
The most
important node types are:
Element type NodeType
Element 1
Attribute 2
Text 3
Comment 8
Document 9
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