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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:
The text inside HTML elements are text nodes Every HTML attribute is an attribute node (deprecated)
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. 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>
Formula
< title > DOM Tutorial </title ></head> <body>
Formula
< 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
You can use the following node properties to navigate between nodes with
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>
<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 document document.documentElement - The full document
<html> <body>
Formula
< 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>
Formula
< 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. 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
<h1 id="id01">My First Page</h1> <p id="id02"></p> <script> document.getElementById("id02").innerHTML
= document.getElementById("id01").nodeName;</script>
nodeName always contains the uppercase tag name of an HTML element.
The nodeValue property specifies the value of a node. nodeValue for element nodes is null nodeValue for text nodes is the text itself nodeValue for attribute nodes is the attribute value
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: