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C # tutorial
With the HTML DOM, you can navigate the node tree using node relationships
According to the W3C HTML DOM standard, everything in an HTML document is a node:
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.
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.
<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 siblingsYou can use the following node properties to navigate between nodes with JavaScript:
parentNode
childNodes[nodenumber]
firstChild
lastChild
nextSibling
previousSibling
A common error in DOM processing is to expect an element node to contain text.
<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:
myTitle = document.getElementById("demo").innerHTML;
Accessing the innerHTML property is the same as accessing the nodeValue
of the first child:
myTitle = document.getElementById("demo").firstChild.nodeValue;
Accessing the first child can also be done like this:
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:
<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>
<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>
<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>
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.
There are two special properties that allow access to the full document:
document.body
- The body of the documentdocument.documentElement
- The full document
<html>
<body>
<h2>JavaScript HTMLDOM</h2>
<p>Displaying document.body</p>
<p
id="demo"></p>
<script>
document.getElementById("demo").innerHTML
= document.body.innerHTML;
</script>
</body>
</html>
<html>
<body>
<h2>JavaScript HTMLDOM</h2>
<p>Displaying document.documentElement</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML =
document.documentElement.innerHTML;
</script>
</body>
</html>
The nodeName
property specifies the name of a node.
<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 specifies the value of a node.
null
The nodeType
property is read only. It returns the type of a node.
<h1 id="id01">My First Page</h1>
<p id="id02"></p>
<script>
document.getElementById("id02").innerHTML
= document.getElementById("id01").nodeType;
</script>
The most important nodeType properties are:
Node | Type | Example |
---|---|---|
ELEMENT_NODE | 1 | <h1 class="heading">w3resource</h1> |
ATTRIBUTE_NODE | 2 | class = "heading" (deprecated) |
TEXT_NODE | 3 | w3resource |
COMMENT_NODE | 8 | <!-- This is a comment --> |
DOCUMENT_NODE | 9 | The HTML document itself (the parent of <html>) |
DOCUMENT_TYPE_NODE | 10 | <!Doctype html> |
Type 2 is deprecated in the HTML DOM (but works). It is not deprecated in the XML DOM.