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14.11 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 (deprecated)
- All comments are comment nodes
Image courtesy www.W3Schools.com
- 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
Image courtesy www.W3Schools.com
<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:
- 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"
- <body> 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:
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 (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 property:
var myTitle = document.getElementById("demo").innerHTML;Accessing the innerHTML property is the same as accessing the 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 1: JS HTML Child Nodes and Node Values part 1
<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 2: JS HTML Child Nodes and Node Values part 2
<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 3: JS HTML Child Nodes and Node Values part 3
<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:
- - The body of the document
- - The full document
Example 4: JS HTMLDOM - DOM Root Nodes part 1
<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.body.innerHTML); </script> </body> </html>
Example 5: JS HTMLDOM - DOM Root Nodes part 2
<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 property specifies the name of a node.
- is read-only
- of an element node is the same as the tag name
- of an attribute node is the attribute name
- of a text node is always #text
- of the document node is always #document
Example 6: JS HTMLDOM - The nodeName Property
<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 property specifies the value of a node.
- nodeValue for element nodes is
- nodeValue for text nodes is the text itself
- nodeValue for attribute nodes is the attribute value
The nodeType Property
The nodeType property is read only. It returns the type of a node.
Example 7: JS HTMLDOM - The nodeType Property
<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">W3Schools</h1> |
| ATTRIBUTE_NODE | 2 | class = "heading" (deprecated) |
| TEXT_NODE | 3 | W3Schools |
| 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.
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