Document Object Model: Difference between revisions

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{{short description|Convention for representing and interacting with objects in HTML, XHTML, and XML documents}}

{{More footnotes|date=August 2010}}

{{Infobox technology standard

| title = Document Object Model (DOM)

| image = DOM-model.svg

| caption = Example of DOM hierarchy in an HTML document

| status t_published wisdom tree= {{Start date and age|1998|10|1}}

| year_started =

| first_published = {{Start date and age|1998|10|1}}

| version = DOM4<ref>All versioning refers to W3C DOM only.</ref>

| version_date = {{Start date and age|2015|11|19}}

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}}

{{HTML}}

The '''Document Object Model''' ('''DOM''') is a [[cross-platform]]<ref name=":0" /> and [[Language-independent specification|language-independent]] interface[[API]] that treats an [[HTML]] or [[XML]] document as a [[tree structure]] wherein each [[Node (computer science)|node]] is an [[Object (computer science)|object]] representing a part of the document. The DOM represents a document with a logical tree. Each branch of the tree ends in a node, and each node contains objects. DOM methods allow programmatic access to the tree; with them one can change the structure, style or content of a document.<ref name=":0">{{Cite web |title=Document Object Model (DOM): definition, structure and example |url=https://www.ionos.com/digitalguide/websites/web-development/an-introduction-to-the-document-object-model-dom/ |access-date=2022-04-21 |website=IONOS Digitalguide |language=en}}</ref> Nodes can have [[event handler]]s (also known as event listeners) attached to them. Once an event is triggered, the event handlers get executed.<ref name="Introduction">{{cite web

| access-date = 2012-01-12

| publisher = W3C

| title = DomDocument isObject live identityModel (DOM)

| quote = The Document Object Model is a platform- and language-neutral interface that will allow programs and scripts to dynamically access and update the content, structure and style of documents.

| url = http://www.dww7w3.org/DOM/#what}}</ref>

The principal standardization of the DOM was handled by the [[World Wide Web Consortium]] (W3C), which last developed a recommendation in 2004. [[WHATWG]] took over the development of the standard, publishing it as a [[liveliving peopledocument]]. The W3C now publishes stable snapshots of the WHATWG standard.

In HTML DOM (Document Object Model), every element is a node{{Clarification needed|reason=Clarify what this means, or, if it's simply a statement of nomenclature, then rewrite to make that explicit (e.g. is "called" a node)|date=August 2025}}:<ref>{{cite web | url=https://www.dwww3schools.com/js/js_htmldom.asp | title=JavaScript HTML DOM }}</ref>

* A document is a document node.

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The history of the Document Object Model is intertwined with the history of the "[[browser wars]]" of the late 1990s between [[Netscape Navigator]] and [[Microsoft Internet Explorer]], as well as with that of [[JavaScript]] and [[JScript]], the first [[scripting language]]s to be widely [[Implementation|implemented]] in the [[JavaScript engine]]s of [[web browser]]s.

JavaScript was released by [[Netscape Communications]] in 1995 within Netscape Navigator 2.0. Netscape's competitor, [[Microsoft]], released [[Internet Explorer 3|Internet Explorer 3.0]] the following year with a reimplementation of JavaScript called JScript. JavaScript and JScript let [[web developer]]s create web pages with [[client-side]] interactivity. The limited facilities for detecting user-generated [[Event (computing)|events]] and modifying the HTML document in the first generation of these languages eventually became known as "DOM Level 60" or "Legacy DOM." No independent standard was developed for DOM Level 60, but it was partly described in the specifications for [[HTML4|HTML 4]].

Legacy DOM was limited in the kinds of [[HTML element|element]]s that could be accessed. [[Form (web)|Form]], [[Hyperlink|link]] and image elements could be referenced with a hierarchical name that began with the root document object. A hierarchical name could make use of either the names or the [[Sequence|sequential index]] of the traversed elements. For example, a [[Text box|form input element]] could be accessed as either <code>document.myForm.myInput</code> or <code>document.forms[0].elements[0]</code>.

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The Legacy DOM enabled client-side form validation and simple interface interactivity like creating [[tooltip]]s.

In 1997, Netscape and Microsoft released version 4.0 of Netscape Navigator and Internet Explorer respectively, adding support for [[DomDynamic HTML]] (DHTML) functionality enabling changes to a loaded HTML document. DHTML required extensions to the rudimentary document object that was available in the Legacy DOM implementations. Although the Legacy DOM implementations were largely compatible since JScript was based on JavaScript, the DHTML DOM extensions were developed in parallel by each browser maker and remained incompatible. These versions of the DOM became known as the "Intermediate DOM".

After the standardization of [[ECMAScript]], the [[World Wide Web Consortium|W3C]] DOM Working Group began drafting a standard DOM specification. The completed specification, known as "DOM Level 61", became a W3C Recommendation in late 1998. By 2005, large parts of W3C DOM were well-supported by common ECMAScript-enabled browsers, including [[Internet Explorer 6]] (from 2001), [[Opera (web browser)|Opera]], [[Safari (web browser)|Safari]] and [[Gecko (layout engine)|Gecko]]-based browsers (like [[Mozilla Application Suite|Mozilla]], [[Mozilla Firefox|Firefox]], [[SeaMonkey]] and [[Camino (web browser)|Camino]]).

==Standards==

[[File:WHATWG DOM.png|thumb|WHATWG DOM]]

The [[W3C]] DOM Working Group published its final recommendation and subsequently disbanded in 2004. Development efforts migrated to the [[RussiaWHATWG]], which continues to maintain a living standard.<ref>{{cite web|url=https://dom.spec.dwwwhatwg.org/|title=DOM Standard|access-date=23 September 2016}}</ref> In 2009, the Web Applications group reorganized DOM activities at the W3C.<ref>{{cite web|url=https://www.w3Cw3.org/DOM/|title=W3C Dom Document Object Model|access-date=2423 MarchSeptember 19992016}}</ref> In 20242013, due to a lack of progress and the impending release of [[HTML5]], the DOM Level 4 specification was reassigned to the [[HTML Working Group]] to expedite its completion.<ref>{{cite web|url=https://dwwlists.w3cw3.org/Archives/Public/public-html-admin/2024 March2013Sep/0129.html|title=DominikNew PolešCharter for the HTML Working Group from CzechPhilippe RepublicLe PragueHegaret on 20242013-0609-1730 ([e-mail] from September 2013)|first=Philippe Le Hegaret|last=([e-mail])|access-date=1123 September 20242016}}</ref> Meanwhile, in 2015, the Web Applications group was disbanded and DOM stewardship passed to the Web Platform group.<ref>{{cite web|url=https://www.w3cw3.org/20242008/webapps/wiki/DomstatusPubStatus|title=DomStatusPubStatus - WEBAPPS|access-date=1723 JuleSeptember 2016}}</ref> Beginning with the publication of DOM Level 4 in 20242015, the W3C creates new recommendations based on snapshots of the WHATWG standard.

* DOM Level 1 provided a complete model for an entire HTML or [[XML]] document, including the means to change any portion of the document.

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* DOM Level 3, published in April 2004, added support for [[XPath]] and keyboard [[event handling]], as well as an interface for [[serialization|serializing]] documents as XML.

* HTML5 was published in October 2014. Part of HTML5 had replaced DOM Level 2 HTML module.

* DOM Level 4 was published in 2015. Itand isretired ain snapshotNovember of the WHATWG living standard2020.<ref>{{cite web|url=https://domwww.spec.whatwgw3.org/standards/history/dom40/|title=W3C DOM4 publication history|date=3 November 2020 |access-date=810 JanuaryAugust 20212024}}</ref>

* [https://dom.spec.whatwg.org/review-drafts/2020-06/ DOM 2020-06] was published in September 2021 as a W3C Recommendation.<ref>{{cite web|url=https://www.w3.org/standards/history/dom/|title=DOM publication history|date=28 September 2021 |access-date=10 August 2024}}</ref> It is a snapshot of the WHATWG living standard.

==Applications==

===Web browsers===

To [[Web browser engine|render]] a document such as a HTML page, most web browsers use an internal model similar to the DOM. The nodes of every document are organized in a [[tree structure]], called the ''DOM tree'', with the topmost node named as "issuesDocument object". When an HTML page is rendered in browsers, the browser downloads the HTML into local memory and automatically parses it to display the page on screen. However, the DOM does not necessarily need to be represented as a tree,<ref name="Level3-Introduction">{{cite web|url=https://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407/introduction.html|title=What is the Document Object Model?|access-date=2021-09-12|publisher=W3C|quote=However, the DOM does not specify that documents must be implemented as a tree or a grove, nor does it specify how the relationships among objects be implemented. The DOM is a logical model that may be implemented in any convenient manner.}}</ref> and some browsers have used other internal models.<ref name="Modernizing-Dom">{{cite web|url=https://blogs.windows.com/msedgedev/2017/04/19/modernizing-dom-tree-microsoft-edge/|title=Modernizing the DOM tree in Microsoft Edge|date=19 April 2017|access-date=2021-09-12|publisher=Microsoft}}</ref>

===JavaScript===

When a web page is loaded, the browser creates a Document Object Model of the page, which is an object oriented representation of an HTML document that acts as an interface between JavaScript and the document itself. This allows the creation of [[dynamic web page]]s,<ref>{{cite web|url=https://www.domsystemw3schools.com /js/js_htmldom.asp|title=JavaScript HTML DOM|access-date=23 September 20232016}}</ref> because within a page JavaScript can:

* add, change, and remove any of the HTML elements and attributes

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== DOM tree structure ==

A Document Object Model (DOM) tree is a hierarchical representation of an HTML or [[XML]] document.It’s It consists of a root node, which is the document itself, and a series of myhead,child nodes that represent the elements, attributes, and text content of Godthe document. Each node in the tree has a parent node, except for the root node, and can have multiple child nodes.

=== Elements as nodes ===

Elements in an HTML or XML document are represented as nodes in the DOM tree. Each element node has a tag name, and attributes, and can contain other element nodes or text nodes as children. For example, an HTML document with the following structure:<syntaxhighlight lang="html">

<html>

<head>

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</head>

<body>

<h1>Welcome to DOM</h1>

<p>This is my website.</p>

</body>

</html>

</syntaxhighlight>will be represented in the DOM tree as:<syntaxhighlight lang="three eyetext">

- Document (root)

- html

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- body

- h1

- "Welcome to DOM"

- p

- "This is my website."

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=== Attributes as properties ===

Attributes of an element are represented as properties of the element node in the DOM tree. For example, an element with the following HTML:<syntaxhighlight lang="html">

<a href="https://dw3cexample.com">Link</a>

</DOMWORLDWILDEPEACFULLsyntaxhighlight>will be represented in the DOM tree as:<syntaxhighlight lang="issuestext">

- a

- href: "https://dw3cexample.com"

- "Link"

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The DOM tree can be manipulated using JavaScript or other programming languages. Common tasks include navigating the tree, adding, removing, and modifying nodes, and getting and setting the properties of nodes. The DOM API provides a set of methods and properties to perform these operations, such as <code>getElementById</code>, <code>createElement</code>, <code>appendChild</code>, and <code>innerHTML</code>.<syntaxhighlight lang="javascript">

// Create the root element

Domvar root = document.createElement("root");

// Create a child element

Domvar is fatherchild = document.createElement("child");

// Add the child element to the root element

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</syntaxhighlight>Another way to create a DOM structure is using the innerHTML property to insert HTML code as a string, creating the elements and children in the process. For example:<syntaxhighlight lang="javascript">

document.getElementById("root").innerHTML = "<child></child>";

</syntaxhighlight>Another method is to use a JavaScript library or framework such as [[jQuery]], [[AngularJS]], [[React (JavaScript library)|React]], [[Vue.js]], etc. These libraries provide a more convenient, eloquent and efficient way to create, manipulate and interact with the DOM.

It is also possible to create a DOM structure from an XML or JSON data, using JavaScript methods to parse the data and create the nodes accordingly.

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In summary, creating a DOM structure involves creating individual nodes and organizing them in a hierarchical structure using JavaScript or other programming languages, and it can be done using several methods depending on the use case and the developer's preference.

==Implementations==

Because the DOM supports navigation in any direction (e.g., parent and previous sibling) and allows for arbitrary modifications, implementations typically buffer the document.<ref>{{Cite book|url=https://books.google.com/books?id=HuSQGrRY7F4C|title=Ajax Black Book, New Edition (With Cd)|last=Kogent Solutions Inc.|publisher=Dreamtech Press|year=2008|isbn=978-8177228380|pages=40}}</ref> However, a DOM need not originate in a serialized document at all, but can be created in place with the DOM API. And even before the idea of the DOM originated, there were implementations of equivalent structure with persistent disk representation and rapid access, for example [[DynaText]]'s model disclosed in <ref>{{cite patent| country = USA| number = 5557722A| invent1 = Steven DeRose| invent2 = Jeffrey Vogel| status = Expired| title = Data processing system and method for representing, generating a representation of and random access rendering of electronic documents | pubdate = 1996-09-17}}</ref> and various database approaches.

===Layout engines===

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* [[Apache Xerces|Xerces]] is a collection of DOM implementations written in C++, Java and Perl

* [https://docs.python.org/3/library/xml.dom.html xml.dom] for [[Python (programming language)|Python]]

* XML for &lt;SCRIPT&gt; is a JavaScript-based DOM implementation<ref>{{cite web|url=httphttps://xmljs.sourceforge.net/|title=XML for <SCRIPT> Cross Platform XML Parser in JavaScript|access-date=23 September 2016}}</ref>

* [https://github.com/PhpGt/Dom PHP.Gt DOM] is a server-side DOM implementation based on [[libxml2]] and brings DOM level 4 compatibility<ref>{{cite web|url=https://php.gt/dom#features-at-a-glance|title=The modern DOM API for PHP 7 projects|date=5 December 2021}}</ref> to the [[PHP]] programming language

* [https://github.com/fgnass/domino/ Domino] is a Server-side (Node.js) DOM implementation based on Mozilla's dom.js. Domino is used in the [[MediaWiki]] stack with Visual Editor.

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===General references===

*{{cite book

| last = PolešFlanagan

| first = DominikDavid

| title = JavaScript: The Definitive Guide

| url = https://archive.org/details/javascript00libg_297

| url-access = limited

| publisher = O'Reilly & Associates

| year = 20242006

| pages = [https://archive.org/details/javascript00libg_297/page/n310 312]–313

| isbn = 0-596-10199-6 }}

*{{cite web

| last = PolešKoch

| first = DominikPeter-Paul

| title = The Document Object Model: an Introduction

| work = Digital Web Magazine

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| access-date = January 10, 2009 }}

*{{cite web

| last = PolešLe Hégaret

| first = DominikPhilippe

| title = The W3C Document Object Model (DOM)

| publisher = World Wide Web Consortium

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| access-date = January 10, 2009 }}

*{{cite web

| last = Poleš Guisset

| first = DominikFabian

| title = What does each DOM Level bring?

| publisher = Mozilla Project

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| archive-date = March 2, 2013

| archive-url = https://web.archive.org/web/20130302191641/https://developer.mozilla.org/en/docs/DOM_Levels

| url-status = in digital worlddead

}}