What is the use of html dom?

What is the DOM?

The Document Object Model [DOM] is a programming interface for web documents. It represents the page so that programs can change the document structure, style, and content. The DOM represents the document as nodes and objects; that way, programming languages can interact with the page.

A web page is a document that can be either displayed in the browser window or as the HTML source. In both cases, it is the same document but the Document Object Model [DOM] representation allows it to be manipulated. As an object-oriented representation of the web page, it can be modified with a scripting language such as JavaScript.

For example, the DOM specifies that the querySelectorAll method in this code snippet must return a list of all the

elements in the document:

const paragraphs = document.querySelectorAll["p"];
// paragraphs[0] is the first 
 element
// paragraphs[1] is the second 
 element, etc.
alert[paragraphs[0].nodeName];

All of the properties, methods, and events available for manipulating and creating web pages are organized into objects. For example, the document object that represents the document itself, any table objects that implement the HTMLTableElement DOM interface for accessing HTML tables, and so forth, are all objects.

The DOM is built using multiple APIs that work together. The core DOM defines the entities describing any document and the objects within it. This is expanded upon as needed by other APIs that add new features and capabilities to the DOM. For example, the HTML DOM API adds support for representing HTML documents to the core DOM, and the SVG API adds support for representing SVG documents.

DOM and JavaScript

The previous short example, like nearly all examples, is JavaScript. That is to say, it is written in JavaScript, but uses the DOM to access the document and its elements. The DOM is not a programming language, but without it, the JavaScript language wouldn't have any model or notion of web pages, HTML documents, SVG documents, and their component parts. The document as a whole, the head, tables within the document, table headers, text within the table cells, and all other elements in a document are parts of the document object model for that document. They can all be accessed and manipulated using the DOM and a scripting language like JavaScript.

The DOM is not part of the JavaScript language, but is instead a Web API used to build websites. JavaScript can also be used in other contexts. For example, Node.js runs JavaScript programs on a computer, but provides a different set of APIs, and the DOM API is not a core part of the Node.js runtime.

The DOM was designed to be independent of any particular programming language, making the structural representation of the document available from a single, consistent API. Even if most web developers will only use the DOM through JavaScript, implementations of the DOM can be built for any language, as this Python example demonstrates:

# Python DOM example
import xml.dom.minidom as m
doc = m.parse[r"C:\Projects\Py\chap1.xml"]
doc.nodeName # DOM property of document object
p_list = doc.getElementsByTagName["para"]

For more information on what technologies are involved in writing JavaScript on the web, see JavaScript technologies overview.

Accessing the DOM

You don't have to do anything special to begin using the DOM. You use the API directly in JavaScript from within what is called a script, a program run by a browser.

When you create a script, whether inline in a element or included in the web page, you can immediately begin using the API for the document or window objects to manipulate the document itself, or any of the various elements in the web page [the descendant elements of the document]. Your DOM programming may be something as simple as the following example, which displays a message on the console by using the console.log[] function:

  …

As it is generally not recommended to mix the structure of the page [written in HTML] and manipulation of the DOM [written in JavaScript], the JavaScript parts will be grouped together here, and separated from the HTML.

For example, the following function creates a new

element, adds text to that element, and then adds it to the tree for the document:

  
    
      // run this function when the document is loaded
      window.onload = [] => {
        // create a couple of elements in an otherwise empty HTML page
        const heading = document.createElement["h2"];
        const headingText = document.createTextNode["Big Head!"];
        heading.appendChild[headingText];
        document.body.appendChild[heading];
      };
    
  
  

Fundamental data types

This page tries to describe the various objects and types in simple terms. But there are a number of different data types being passed around the API that you should be aware of.

Note: Because the vast majority of code that uses the DOM revolves around manipulating HTML documents, it's common to refer to the nodes in the DOM as elements, although strictly speaking not every node is an element.

The following table briefly describes these data types.

There are also some common terminology considerations to keep in mind. It's common to refer to any Attr node as an attribute, for example, and to refer to an array of DOM nodes as a nodeList. You'll find these terms and others to be introduced and used throughout the documentation.

DOM interfaces

This guide is about the objects and the actual things you can use to manipulate the DOM hierarchy. There are many points where understanding how these work can be confusing. For example, the object representing the HTML form element gets its name property from the HTMLFormElement interface but its className property from the HTMLElement interface. In both cases, the property you want is in that form object.

But the relationship between objects and the interfaces that they implement in the DOM can be confusing, and so this section attempts to say a little something about the actual interfaces in the DOM specification and how they are made available.

Interfaces and objects

Many objects borrow from several different interfaces. The table object, for example, implements a specialized HTMLTableElement interface, which includes such methods as createCaption and insertRow. But since it's also an HTML element, table implements the Element interface described in the DOM Element Reference chapter. And finally, since an HTML element is also, as far as the DOM is concerned, a node in the tree of nodes that make up the object model for an HTML or XML page, the table object also implements the more basic Node interface, from which Element derives.

When you get a reference to a table object, as in the following example, you routinely use all three of these interfaces interchangeably on the object, perhaps without knowing it.

const table = document.getElementById["table"];
const tableAttrs = table.attributes; // Node/Element interface
for [let i = 0; i 
  
  Set text content
  Clear text content

CSS

.container {
  display: flex;
  gap: 0.5rem;
  flex-direction: column;
}

button {
  width: 200px;
}

JavaScript

const story = document.body.querySelector[".story"];

const setText = document.body.querySelector["#set-text"];
setText.addEventListener["click", [] => {
  story.textContent = "It was a dark and stormy night...";
}];

const clearText = document.body.querySelector["#clear-text"];
clearText.addEventListener["click", [] => {
  story.textContent = "";
}];

Result

Adding a child element

This example uses a

  parent
  Add a child
  Remove child

.container {
  display: flex;
  gap: 0.5rem;
  flex-direction: column;
}

button {
  width: 100px;
}

div.parent {
  border: 1px solid black;
  padding: 5px;
  width: 100px;
  height: 100px;
}

div.child {
  border: 1px solid red;
  margin: 10px;
  padding: 5px;
  width: 80px;
  height: 60px;
  box-sizing: border-box;
}

const parent = document.body.querySelector[".parent"];

const addChild = document.body.querySelector["#add-child"];
addChild.addEventListener["click", [] => {
  // Only add a child if we don't already have one
  // in addition to the text node "parent"
  if [parent.childNodes.length > 1] {
    return;
  }
  const child = document.createElement["div"];
  child.classList.add["child"];
  child.textContent = "child";
  parent.appendChild[child];
}];

const removeChild = document.body.querySelector["#remove-child"];
removeChild.addEventListener["click", [] => {
  const child = document.body.querySelector[".child"];
  parent.removeChild[child];
}];