Dom structures

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DOM STRUCTURE

Document Object Model (DOM)
• The Document Object Model (DOM) is a programming API for
HTML and XML documents.
• Defines the logical structure of documents and the way a
document is accessed and manipulated.
• An interface to allow programs and scripts to update content,
structure, and style of documents dynamically.
• The DOM is not HTML nor is it JavaScript.
• It is something like the glue that binds them together.

DOM Objects
• DOM components are accessible as objects or
collections of objects.
• In HTML DOM
o The entire document is a document node.
o Every HTML element is an element node.
o The Every HTML attribute is an attribute node
o text inside HTML elements are text nodes.
o Comments are comment nodes.

• DOM components form a tree of nodes called Node
Tree
• nodes in the node tree have a hierarchical relationship to
each other.
i.e, Parent node, child node and siblings
Fig : HTML DOM tree
example.

Fig : image illustrates a part of the node tree and the relationship between the nodes.

Programming Interface
• All HTML elements are defined as objects.
• the programming interface is the object methods and object
properties.
• A method is an action you can do.
• A property is a value that you can get or set.

getElementById(id) get the node (element) with a
specified id
appendChild(node) insert a new child node (element)
removeChild(node) remove a child node (element)
•HTML DOM methods:
•HTML DOM properties:
innerHTML the text value of a node (element)
parentNode the parent node of a node
(element)
childNodes the child nodes of a node (element)
attributes the attributes nodes of a node
(element)

Accessing Nodes by id
• Access to elements by their id
– document.getElementById(<id>)
• returns the element with id <id>
– id attribute can be defined in each start tag.

Other Access Methods
• Access by elements' tag
– there are typically several elements with the same tag
– document.getElementsByTagName(<tag>)
– e.g.
• var li = document.getElementsByTagName(“li")[0];
//to get first li of ul.
• Access by elements' name attribute
– several elements can have the same name
– document.getElementsByName(<name>)
• returns the collection of elements with name <name>

Traversing DOM tree
• Traversal through node properties
– childNodes property
• the value is a collection of nodes
– has a length attribute
– an item can be reached by its index
• e.g. var body = html.childNodes[1];
– firstChild, lastChild properties
– nextSibling, previousSibling properties
– parentNode property

Document Object Model
<TABLE>
<ROWS>
<TR>
<TD>hi</TD>
<TD>there</TD>
</TR>
<TR>
<TD>hello</TD>
<TD>world</TD>
</TR>
</ROWS>
</TABLE>

Eg :JavaScript program to add two numbers.( Numbers are input
using textbox )
<html>
<head>
<script language="javascript">
function calculateNumbers()
{
var FirstNumber = document.getElementById("txtFirst").value;
FirstNumber = Number(FirstNumber);
var SecondNumber = document.getElementById("txtSecond").value;
SecondNumber = Number(SecondNumber);
var Total = (FirstNumber+SecondNumber);
document.frmCalculate.txtTotal.value = Total;
}
</script>
</head>
<body>
<form name="frmCalculate">
<input type="text" size="2" id="txtFirst" maxlength="2">+</input>
<input type="text" size="2" id="txtSecond" maxlength="2">=</input>
<input type="text" size="2" name="txtTotal" ></input><br>
<input type="button" value="Add" name="buttonCalculate"
onClick="calculateNumbers()"></input>
<input type="reset" value="Reset" name="buttonReset"></input>
</form>
</body>
</html>

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