HTML DOM Access Nodes
With the DOM, you can access every node in an HTML document.
Accessing Nodes
You can access a node in three ways:
1. By using the getElementById() method
2. By using the getElementsByTagName() method
3. By navigating the node tree, using the node relationships.
The getElementById() Method
The getElementById() method returns the element with the specified ID:
Syntax
document.getElementById("someID");
|
Try it
yourself.
Note: The getElementById() method doesn't work in XML.
The getElementsByTagName() Method
getElementsByTagName() returns all elements with a specified tag name.
Syntax
node.getElementsByTagName("tagname");
|
Example 1
The following example returns a nodeList of all <p> elements in the document:
document.getElementsByTagName("p");
|
Try it
yourself.
Example 2
The following example returns a nodeList of all <p> elements that are descendants of
the element with id="main":
document.getElementById('main').getElementsByTagName("p");
|
Try it
yourself.
DOM Node List
The getElementsByTagName() method returns a node list. A node list is an
array of nodes.
The following code stores a list of <p> nodes (a node list) in the variable
x:
x=document.getElementsByTagName("p");
|
The <p> elements in x can be accessed by index number. To access the
second
<p> you can write:
Try it
yourself.
Note: The index starts at 0.
You will learn more about node lists in a later chapter of this tutorial.
DOM Node List Length
The length property defines the length of a node list (the number of nodes).
You can loop through the a node list by using the length property:
x=document.getElementsByTagName("p");
for (i=0;i<x.length;i++)
{
document.write(x[i].childNodes[0].nodeValue);
document.write("<br />");
}
|
Example explained:
- Get all <p> element nodes
- For each <p> element, output the value of its text node
Try it yourself.
Navigating Node Relationships
The three properties parentNode, firstChild,
and lastChild follow the document structure and allow short-distance travel in
the document.
Look at the following HTML fragment:
<html>
<body>
<p id="intro">W3Schools example</p>
<div id="main">
<p id="main1">The DOM is very useful</p>
<p id="main2">This example demonstrates <b>node relationships</b></p>
</div>
</body>
</html>
|
In the HTML code above, the <p id="intro"> is the first child node (firstChild) of the <body>
element, and the <div> element is the last child node (lastChild) of the <body> element.
Furthermore, the <body> is the parent (parentNode) of the every <td> element.
The firstChild property can be used to access the text of an
element:
var x=document.getElementById("intro");
var text=x.firstChild.nodeValue;
|
Try
it yourself.
Root Nodes
There are two special document properties that allow access to the
tags:
- document.documentElement
- document.body
The first property returns the root node of the document and exists in
all XML and HTML documents.
The second property is a special addition for HTML pages, and gives
direct access to the <body> tag.
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