The HTML DOM API
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This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
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TheHTML DOM API is made up of the interfaces that define the functionality of each of theelements inHTML, as well as any supporting types and interfaces they rely upon.
The functional areas included in the HTML DOM API include:
- Access to and control of HTML elements via theDOM.
- Access to and manipulation of form data.
- Interacting with the contents of 2D images and the context of an HTML
<canvas>, for example to draw on top of them. - Management of media connected to the HTML media elements (
<audio>and<video>). - Dragging and dropping of content on webpages.
- Access to the browser navigation history
- Supporting and connective interfaces for other APIs such asWeb Components,Web Storage,Web Workers,WebSocket, andServer-sent events.
HTML DOM concepts and usage
In this article, we'll focus on the parts of the HTML DOM that involve engaging with HTML elements. Discussion of other areas, such asDrag and Drop,WebSockets,Web Storage, etc. can be found in the documentation for those APIs.
Structure of an HTML document
The Document Object Model (DOM) is an architecture that describes the structure of adocument; each document is represented by an instance of the interfaceDocument. A document, in turn, consists of a hierarchical tree ofnodes, in which a node is a fundamental record representing a single object within the document (such as an element or text node).
Nodes may be strictly organizational, providing a means for grouping other nodes together or for providing a point at which a hierarchy can be constructed; other nodes may represent visible components of a document. Each node is based on theNode interface, which provides properties for getting information about the node as well as methods for creating, deleting, and organizing nodes within the DOM.
Nodes don't have any concept of including the content that is actually displayed in the document. They're empty vessels. The fundamental notion of a node that can represent visual content is introduced by theElement interface. AnElement object instance represents a single element in a document created using either HTML or anXML vocabulary such asSVG.
For example, consider a document with two elements, one of which has two more elements nested inside it:
While theDocument interface is defined as part of theDOM specification, the HTML specification significantly enhances it to add information specific to using the DOM in the context of a web browser, as well as to using it to represent HTML documents specifically.
Among the things added toDocument by the HTML standard are:
- Support for accessing various information provided by theHTTP headers when loading the page, such as thelocation from which the document was loaded,cookies,modification date,referring site, and so forth.
- Access to lists of elements in the document's
<head>block andbody, as well as lists of theimages,links,scripts, etc. contained in the document. - Support for interacting with the user by examiningfocus and by executing commands oneditable content.
- Event handlers for document events defined by the HTML standard to allow access tomouse andkeyboard events,drag and drop,media control, and more.
- Event handlers for events that can be delivered to both elements and documents; these presently include only
copy,cut, andpasteactions.
HTML element interfaces
TheElement interface has been further adapted to represent HTML elements specifically by introducing theHTMLElement interface, which all more specific HTML element classes inherit from. This expands theElement class to add HTML-specific general features to the element nodes. Properties added byHTMLElement include for examplehidden andinnerText.
AnHTML document is a DOM tree in which each of the nodes is an HTML element, represented by theHTMLElement interface. TheHTMLElement class, in turn, implementsNode, so every element is also a node (but not the other way around). This way, the structural features implemented by theNode interface are also available to HTML elements, allowing them to be nested within each other, created and deleted, moved around, and so forth.
TheHTMLElement interface is generic, however, providing only the functionality common to all HTML elements such as the element's ID, its coordinates, the HTML making up the element, information about scroll position, and so forth.
In order to expand upon the functionality of the coreHTMLElement interface to provide the features needed by a specific element, theHTMLElement class is subclassed to add the needed properties and methods. For example, the<canvas> element is represented by an object of typeHTMLCanvasElement.HTMLCanvasElement augments theHTMLElement type by adding properties such asheight and methods likegetContext() to provide canvas-specific features.
The overall inheritance for HTML element classes looks like this:
As such, an element inherits the properties and methods of all of its ancestors. For example, consider an<a> element, which is represented in the DOM by an object of typeHTMLAnchorElement. The element, then, includes the anchor-specific properties and methods described in that class's documentation, but also those defined byHTMLElement andElement, as well as fromNode and, finally,EventTarget.
Each level defines a key aspect of the utility of the element. FromNode, the element inherits concepts surrounding the ability for the element to be contained by another element, and to contain other elements itself. Of special importance is what is gained by inheriting fromEventTarget: the ability to receive and handle events such as mouse clicks, play and pause events, and so forth.
There are elements that share commonalities and thus have an additional intermediary type. For example, the<audio> and<video> elements both present audiovisual media. The corresponding types,HTMLAudioElement andHTMLVideoElement, are both based upon the common typeHTMLMediaElement, which in turn is based uponHTMLElement and so forth.HTMLMediaElement defines the methods and properties held in common between audio and video elements.
These element-specific interfaces make up the majority of the HTML DOM API, and are the focus of this article. To learn more about the actual structure of theDOM, seeIntroduction to the DOM.
HTML DOM target audience
The features exposed by the HTML DOM are among the most commonly-used APIs in a web developer's toolkit.All but the most simple web applications will use some features of the HTML DOM.
HTML DOM API interfaces
The majority of the interfaces that comprise the HTML DOM API map almost one-to-one to individual HTML elements, or to a small group of elements with similar functionality. In addition, the HTML DOM API includes a few interfaces and types to support the HTML element interfaces.
HTML element interfaces
These interfaces represent specific HTML elements (or sets of related elements which have the same properties and methods associated with them).
HTMLAnchorElementHTMLAreaElementHTMLAudioElementHTMLBaseElementHTMLBodyElementHTMLBRElementHTMLButtonElementHTMLCanvasElementHTMLDataElementHTMLDataListElementHTMLDetailsElementHTMLDialogElementHTMLDirectoryElementHTMLDivElementHTMLDListElementHTMLElementHTMLEmbedElementHTMLFieldSetElementHTMLFormElementHTMLHRElementHTMLHeadElementHTMLHeadingElementHTMLHtmlElementHTMLIFrameElementHTMLImageElementHTMLInputElementHTMLLabelElementHTMLLegendElementHTMLLIElementHTMLLinkElementHTMLMapElementHTMLMediaElementHTMLMenuElementHTMLMetaElementHTMLMeterElementHTMLModElementHTMLObjectElementHTMLOListElementHTMLOptGroupElementHTMLOptionElementHTMLOutputElementHTMLParagraphElementHTMLPictureElementHTMLPreElementHTMLProgressElementHTMLQuoteElementHTMLScriptElementHTMLSelectElementHTMLSlotElementHTMLSourceElementHTMLSpanElementHTMLStyleElementHTMLTableCaptionElementHTMLTableCellElementHTMLTableColElementHTMLTableElementHTMLTableRowElementHTMLTableSectionElementHTMLTemplateElementHTMLTextAreaElementHTMLTimeElementHTMLTitleElementHTMLTrackElementHTMLUListElementHTMLUnknownElementHTMLVideoElement
Deprecated HTML Element Interfaces
Obsolete HTML Element Interfaces
Web app and browser integration interfaces
These interfaces offer access to the browser window and document that contain the HTML, as well as to the browser's state, available plugins (if any), and various configuration options.
Deprecated web app and browser integration interfaces
Obsolete web app and browser integration interfaces
Form support interfaces
Canvas and image interfaces
Media interfaces
Drag and drop interfaces
These interfaces are used by theHTML Drag and Drop API to represent individual draggable (or dragged) items, groups of dragged or draggable items, and to handle the drag and drop process.
Page history interfaces
The History API interfaces let you access information about the browser's history, as well as to shift the browser's current tab forward and backward through that history.
Web Components interfaces
These interfaces are used by theWeb Components API to create and manage the availablecustom elements.
Miscellaneous and supporting interfaces
These supporting object types are used in a variety of ways in the HTML DOM API. In addition,PromiseRejectionEvent represents the event delivered when aJavaScriptPromise is rejected.
Interfaces belonging to other APIs
Several interfaces are technically defined in the HTML specification while actually being part of other APIs.
Web storage interfaces
TheWeb Storage API provides the ability for websites to store data either temporarily or permanently on the user's device for later re-use.
Web Workers interfaces
These interfaces are used by theWeb Workers API both to establish the ability for workers to interact with an app and its content, but also to support messaging between windows or apps.
BroadcastChannelDedicatedWorkerGlobalScopeMessageChannelMessageEventMessagePortSharedWorkerSharedWorkerGlobalScopeWorkerWorkerGlobalScopeWorkerLocationWorkerNavigator
WebSocket interfaces
These interfaces, defined by the HTML specification, are used by theWebSockets API.
Server-sent events interfaces
TheEventSource interface represents the source which sent or is sendingserver-sent events.
Examples
JavaScript
const nameField = document.getElementById("userName");const sendButton = document.getElementById("sendButton");sendButton.disabled = true;// [note: this is disabled since it causes this article to always load with this example focused and scrolled into view]// nameField.focus();nameField.addEventListener("input", (event) => { const elem = event.target; const valid = elem.value.length !== 0; if (valid && sendButton.disabled) { sendButton.disabled = false; } else if (!valid && !sendButton.disabled) { sendButton.disabled = true; }});This code uses theDocument interface'sgetElementById() method to get the DOM object representing the<input> elements whose IDs areuserName andsendButton. With these, we can access the properties and methods that provide information about and grant control over these elements.
TheHTMLInputElement object for the "Send" button'sdisabled property is set totrue, which disables the "Send" button so it can't be clicked. In addition, the user name input field is made the active focus by calling thefocus() method it inherits fromHTMLElement.
ThenaddEventListener() is called to add a handler for theinput event to the user name input. This code looks at the length of the current value of the input; if it's zero, then the "Send" button is disabled if it's not already disabled. Otherwise, the code ensures that the button is enabled.
With this in place, the "Send" button is always enabled whenever the user name input field has a value, and disabled when it's empty.
HTML
The HTML for the form looks like this:
<p>Please provide the information below. Items marked with "*" are required.</p><form action="" method="get"> <p> <label for="userName" required>Your name:</label> <input type="text" /> (*) </p> <p> <label for="userEmail">Email:</label> <input type="email" /> </p> <input type="submit" value="Send" /></form>Result
Specifications
| Specification |
|---|
| HTML # htmlelement |