| Document Object Model (DOM) | |
|---|---|
 Example of DOM hierarchy in an HTML document | |
| Abbreviation | DOM |
| Latest version | DOM4[1] November 19, 2015; 10 years ago (2015-11-19) |
| Organization | World Wide Web Consortium,WHATWG |
| Base standards | WHATWG DOM Living Standard W3C DOM4 |
| HTML |
|---|
 |
| HTML and variants |
| HTML elements and attributes |
| Editing |
| Character encodings and language |
| Document and browser models |
| Client-side scripting and APIs |
| Graphics and Web3D technology |
| Comparisons |
TheDocument Object Model (DOM) is across-platform[2] andlanguage-independentAPI that treats anHTML orXML document as atree structure wherein eachnode is anobject 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.[2] Nodes can haveevent handlers (also known as event listeners) attached to them. Once an event is triggered, the event handlers get executed.[3]
The principal standardization of the DOM was handled by theWorld Wide Web Consortium (W3C), which last developed a recommendation in 2004.WHATWG took over the development of the standard, publishing it as aliving document. The W3C now publishes stable snapshots of the WHATWG standard.
In HTML DOM (Document Object Model), every element is a node[clarification needed]:[4]
The history of the Document Object Model is intertwined with the history of the "browser wars" of the late 1990s betweenNetscape Navigator andMicrosoft Internet Explorer, as well as with that ofJavaScript andJScript, the firstscripting languages to be widelyimplemented in theJavaScript engines ofweb browsers.
JavaScript was released byNetscape Communications in 1995 within Netscape Navigator 2.0. Netscape's competitor,Microsoft, releasedInternet Explorer 3.0 the following year with a reimplementation of JavaScript called JScript. JavaScript and JScript letweb developers create web pages withclient-side interactivity. The limited facilities for detecting user-generatedevents and modifying the HTML document in the first generation of these languages eventually became known as "DOM Level 0" or "Legacy DOM." No independent standard was developed for DOM Level 0, but it was partly described in the specifications forHTML 4.
Legacy DOM was limited in the kinds ofelements that could be accessed.Form,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 thesequential index of the traversed elements. For example, aform input element could be accessed as eitherdocument.myForm.myInput ordocument.forms[0].elements[0].
The Legacy DOM enabled client-side form validation and simple interface interactivity like creatingtooltips.
In 1997, Netscape and Microsoft released version 4.0 of Netscape Navigator and Internet Explorer respectively, adding support forDynamic 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 ofECMAScript, theW3C DOM Working Group began drafting a standard DOM specification. The completed specification, known as "DOM Level 1", became a W3C Recommendation in late 1998. By 2005, large parts of W3C DOM were well-supported by common ECMAScript-enabled browsers, includingInternet Explorer 6 (from 2001),Opera,Safari andGecko-based browsers (likeMozilla,Firefox,SeaMonkey andCamino).
TheW3C DOM Working Group published its final recommendation and subsequently disbanded in 2004. Development efforts migrated to theWHATWG, which continues to maintain a living standard.[5] In 2009, the Web Applications group reorganized DOM activities at the W3C.[6] In 2013, due to a lack of progress and the impending release ofHTML5, the DOM Level 4 specification was reassigned to theHTML Working Group to expedite its completion.[7] Meanwhile, in 2015, the Web Applications group was disbanded and DOM stewardship passed to the Web Platform group.[8] Beginning with the publication of DOM Level 4 in 2015, the W3C creates new recommendations based on snapshots of the WHATWG standard.
getElementById function as well as anevent model and support forXML namespaces and CSS.Torender 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 atree structure, called theDOM tree, with the topmost node named as "Document 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,[11] and some browsers have used other internal models.[12]
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 ofdynamic web pages,[13] because within a page JavaScript can:
A Document Object Model (DOM) tree is a hierarchical representation of an HTML orXML document. It consists of a root node, which is the document itself, and a series of child nodes that represent the elements, attributes, and text content of the document. Each node in the tree has a parent node, except for the root node, and can have multiple child 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:
<html><head><title>My Website</title></head><body><h1>Welcome to DOM</h1><p>This is my website.</p></body></html>
will be represented in the DOM tree as:
- Document (root) - html - head - title - "My Website" - body - h1 - "Welcome to DOM" - p - "This is my website."
Text content within an element is represented as a text node in the DOM tree. Text nodes do not have attributes or child nodes, and are always leaf nodes in the tree. For example, the text content "My Website" in the title element and "Welcome" in the h1 element in the above example are both represented as text nodes.
Attributes of an element are represented as properties of the element node in the DOM tree. For example, an element with the following HTML:
<ahref="https://example.com">Link</a>
will be represented in the DOM tree as:
- a - href: "https://example.com" - "Link"
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 asgetElementById,createElement,appendChild, andinnerHTML.
// Create the root elementvarroot=document.createElement("root");// Create a child elementvarchild=document.createElement("child");// Add the child element to the root elementroot.appendChild(child);
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:
document.getElementById("root").innerHTML="<child></child>";
Another method is to use a JavaScript library or framework such asjQuery,AngularJS,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.
Creating a DOM structure does not necessarily mean that it will be displayed in the web page, it only exists in memory and should be appended to the document body or a specific container to be rendered.
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.
Because the DOM supports navigation in any direction (e.g., parent and previous sibling) and allows for arbitrary modifications, implementations typically buffer the document.[14] 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 exampleDynaText's model disclosed in[15] and various database approaches.
Web browsers rely onlayout engines to parse HTML into a DOM. Some layout engines, such asTrident/MSHTML, are associated primarily or exclusively with a particular browser, such as Internet Explorer. Others, includingBlink,WebKit, andGecko, are shared by a number of browsers, such asGoogle Chrome,Opera,Safari, andFirefox. The different layout engines implement the DOM standards to varying degrees of compliance.
DOM implementations:
APIs that expose DOM implementations:
org.w3c.dom) is an API for accessing DOM providersInspection tools:
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.
{{cite web}}: CS1 maint: numeric names: authors list (link)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.
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