HTML DOM, allows JavaScript to access and modify all the elements in an HTML document.
In this article, we will discuss DOM along with its properties and methods used to manipulate documents and understand their implementation through the examples.
Note: It is called a Logical structure because DOM doesn’t specify any relationship between objects.
Table of Content
What is DOM?
The Document Object Model (DOM) is a programming interface for HTML(HyperText Markup Language) and XML(Extensible Markup Language) documents. It defines the logical structure of documents and the way a document is accessed and manipulated.
So basically Document Object Model is an API that represents and interacts with HTML or XML documents.
The DOM is a W3C (World Wide Web Consortium) standard and it defines a standard for accessing documents.
The W3C Dom standard is divided into three different parts:
- Core DOM – standard model for all document types
- XML DOM – standard model for XML documents
- HTML DOM – standard model for HTML documents
HTML DOM
HTML DOM is a standard object model and programming interface for HTML documents. HTML DOM is a way to represent the webpage in a structured hierarchical way so that it will become easier for programmers and users to glide through the document.
With HTML DOM, we can easily access and manipulate tags, IDs, classes, attributes, or elements of HTML using commands or methods provided by the document object.
Using DOM JavaScript we get access to HTML as well as CSS of the web page and can also modify the behavior of the HTML elements.
Why is DOM Required?
HTML is used to structure the web pages and Javascript is used to add behavior to our web pages. When an HTML file is loaded into the browser, the JavaScript can not understand the HTML document directly. So it interprets and interacts with the Document Object Model (DOM), which is created by the browser based on the HTML document.
DOM is basically the representation of the same HTML document but in a tree-like structure composed of objects. JavaScript can not understand the tags(<h1>H</h1>) in HTML document but can understand object h1 in DOM.
JavaScript interprets DOM easily, using it as a bridge to access and manipulate the elements. DOM Javascript allow access to each of the objects (h1, p, etc) by using different functions.
The Document Object Model (DOM) is essential in web development for several reasons:
- Dynamic Web Pages: It allows you to create dynamic web pages. It enables the JavaScript to access and manipulate page content, structure, and style dynamically which gives interactive and responsive web experiences, such as updating content without reloading the entire page or responding to user actions instantly.
- Interactivity: With the DOM, you can respond to user actions (like clicks, inputs, or scrolls) and modify the web page accordingly.
- Content Updates: When you want to update the content without refreshing the entire page, the DOM enables targeted changes making the web applications more efficient and user-friendly.
- Cross-Browser Compatibility: Different browsers may render HTML and CSS in different ways. The DOM provides a standardized way to interact with page elements.
- Single-Page Applications (SPAs): Applications built with frameworks such as React or Angular, heavily rely on the DOM for efficient rendering and updating of content within a single HTML page without reloading the full page.
Structure of DOM
DOM can be thought of as a Tree or Forest (more than one tree). The term structure model is sometimes used to describe the tree-like representation of a document.
Each branch of the tree ends in a node, and each node contains objects Event listeners can be added to nodes and triggered on an occurrence of a given event. One important property of DOM structure models is structural isomorphism: if any two DOM implementations are used to create a representation of the same document, they will create the same structure model, with precisely the same objects and relationships.
Why DOM is called an Object Model?
Documents are modeled using objects, and the model includes not only the structure of a document but also the behavior of a document and the objects of which it is composed like tag elements with attributes in HTML.
Properties of DOM
Let’s see the properties of the document object that can be accessed and modified by the document object.
Representation of the DOM
- Window Object: Window Object is object of the browser which is always at top of the hierarchy. It is like an API that is used to set and access all the properties and methods of the browser. It is automatically created by the browser.
- Document object: When an HTML document is loaded into a window, it becomes a document object. The ‘document’ object has various properties that refer to other objects which allow access to and modification of the content of the web page. If there is a need to access any element in an HTML page, we always start with accessing the ‘document’ object. Document object is property of window object.
- Form Object: It is represented by form tags.
- Link Object: It is represented by link tags.
- Anchor Object: It is represented by a href tags.
- Form Control Elements: Form can have many control elements such as text fields, buttons, radio buttons, checkboxes, etc.
Methods of Document Object
DOM provides various methods that allows users to interact with and manipulate the document. Some commonly used DOM methods are:
- write(“string”): Writes the given string on the document.
- getElementById(): returns the element having the given id value.
- getElementsByName(): returns all the elements having the given name value.
- getElementsByTagName(): returns all the elements having the given tag name.
- getElementsByClassName(): returns all the elements having the given class name.
Example
In this example, We use HTML element id to find the DOM HTML element.
<!DOCTYPE html> <html>
<body>
<h2>GeeksforGeeks</h2>
<!-- Finding the HTML Elements by their Id in DOM -->
<p id="intro">A Computer Science portal for geeks.</p>
<p>This example illustrates the <b>getElementById</b> method.</p>
<p id="demo"></p>
<script>
const element = document.getElementById("intro");
document.getElementById("demo").innerHTML =
"GeeksforGeeks introduction is: " + element.innerHTML;
</script>
</body>
</html>
|
Output:
Getting the HTML element by getElementById() Method
Example
This example describes the representation of the HTML elements in the tree structure.
<table>
<ROWS>
<tr>
<td>Car</td>
<td>Scooter</td>
</tr>
<tr>
<td>MotorBike</td>
<td>Bus</td>
</tr>
</ROWS>
</table>
|
HTML elements in tree-like structure
What DOM is not?
- The Document Object Model is not a binary description where it does not define any binary source code in its interfaces.
- The Document Object Model is not used to describe objects in XML or HTML whereas the DOM describes XML and HTML documents as objects.
- The Document Object Model is not represented by a set of data structures; it is an interface that specifies object representation.
- The Document Object Model does not show the criticality of objects in documents i.e it doesn’t have information about which object in the document is appropriate to the context and which is not.
Levels of DOM
DOM consisted of multiple levels, each representing different aspect of the document.
- Level 0: Provides a low-level set of interfaces.
-
Level 1: DOM level 1 can be described in two parts: CORE and HTML.
- CORE provides low-level interfaces that can be used to represent any structured document.
- HTML provides high-level interfaces that can be used to represent HTML documents.
-
Level 2: consists of six specifications: CORE2, VIEWS, EVENTS, STYLE, TRAVERSAL, and RANGE.
- CORE2: extends the functionality of CORE specified by DOM level 1.
- VIEWS: views allows programs to dynamically access and manipulate the content of the document.
- EVENTS: Events are scripts that are either executed by the browser when the user reacts to the web page.
- STYLE: allows programs to dynamically access and manipulate the content of style sheets.
- TRAVERSAL: This allows programs to dynamically traverse the document.
- RANGE: This allows programs to dynamically identify a range of content in the document.
-
Level 3: consists of five different specifications: CORE3, LOAD and SAVE, VALIDATION, EVENTS, and XPATH.
- CORE3: extends the functionality of CORE specified by DOM level 2.
- LOAD and SAVE: This allows the program to dynamically load the content of the XML document into the DOM document and save the DOM Document into an XML document by serialization.
- VALIDATION: This allows the program to dynamically update the content and structure of the document while ensuring the document remains valid.
- EVENTS: extends the functionality of Events specified by DOM Level 2.
- XPATH: XPATH is a path language that can be used to access the DOM tree.
Example
This example illustrates the dom-manipulation using getElementById() Method.
<!DOCTYPE html> <html>
<head>
<title>DOM manipulation</title>
</head>
<body>
<label>Enter Value 1: </label>
<input type="text" id="val1" />
<br />
<br />
<label>Enter Value 2: </label>
<input type=".text" id="val2" />
<br />
<button onclick="getAdd()">Click To Add</button>
<p id="result"></p>
<script type="text/javascript">
function getAdd() {
// Fetch the value of input with id val1
const num1 = Number(document.getElementById("val1").value);
// Fetch the value of input with id val2
const num2 = Number(document.getElementById("val2").value);
const add = num1 + num2;
console.log(add);
// Displays the result in paragraph using dom
document.getElementById("result").innerHTML = "Addition : " + add;
// Changes the color of paragraph tag with red
document.getElementById("result").style.color = "red";
}
</script>
</body>
</html>
|
Output:
Manipulating the Document objects using getElementById() Method
Conclusion
DOM is a programming interface for web documents. It allows us to modify HTML or XML document using functions. In this guide, we specifically cover HTML DOM, that allows us to manipulate HTML tags, attributes or elements using JavaScript.
We have covered DOM, its properties, structure, methods with examples. Understanding DOM and it’s benefits allow developers to get complete idea of web development. Modify HTML and CSS elements with DOM JavaScript.
Frequently Asked Questions on DOM
What do you mean by DOM?
DOM stands for Document Object Model. It is a programming interface for web documents like HTML, XML and SVG documents. DOM represents elements of documents as tree of objects.
What is an example of a DOM?
DOM representation for a HTML code can be seen as:
Document
– HTML
– head
– title (text: “My Website”)
– body
– h1 (text: “Welcome!”)
– p (text: “This is the main content.”)
What is DOM in JavaScript?
DOM in JavaScript refers to a programming interface. It provides a way to access, manipulate, and interact with the structure and content of an HTML document.
Why DOM is used in JavaScript?
DOM is used in JavaScript for many purposes like: Dynamically style and update content, performing client-side validation, event handling, etc.