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+---
+title: The HTML DOM API
+slug: Web/API/HTML_DOM_API
+tags:
+  - API
+  - Beginner
+  - DOM
+  - Documents
+  - Elements
+  - HTML DOM
+  - HTML DOM API
+  - Nodes
+  - Overview
+  - Web
+  - Windows
+  - hierarchy
+translation_of: Web/API/HTML_DOM_API
+---
+<p>{{DefaultAPISidebar("HTML DOM")}}</p>
+
+<p><strong>HTML DOM API</strong> HTML DOM API は、{{Glossary("HTML")}} の各{{Glossary("element", "要素")}}の機能を定義するインターフェイスと、それらが依存する補助的な型やインターフェイスから構成されています。</p>
+
+<p>HTML DOM API に含まれる機能領域には、以下のようなものがあります。</p>
+
+<ul>
+ <li>{{Glossary("DOM")}} を介した HTML 要素へのアクセスと制御。</li>
+ <li>フォーム データへのアクセスと操作。</li>
+ <li>2D 画像の内容と HTML の {{HTMLElement("canvas")}} のコンテキストとの相互作用、例えば、それらの上に描画すること。</li>
+ <li>HTML のメディア要素 ({{HTMLElement("audio")}} と {{HTMLElement("video")}} に接続されたメディアの管理。</li>
+ <li>ウェブページ上のコンテンツのドラッグ＆ドロップ。</li>
+ <li>ブラウザーのナビゲーション履歴へのアクセス。</li>
+ <li><a href="/ja/docs/Web/Web_Components">ウェブコンポーネント</a>、{{DOMxRef("Web_Storage_API", "ウェブストレージ", "", "1")}}、{{DOMxRef("Web_Workers_API", "ウェブワーカー", "", "1")}}、{{DOMxRef("WebSockets_API", "ウェブソケット", "", "1")}}、{{DOMxRef("Server-sent_events", "サーバー側イベント", "", "1")}} などの他の API のサポートおよび接続インターフェース。</li>
+</ul>
+
+<h2 id="HTML_DOM_concepts_and_usage" name="HTML_DOM_concepts_and_usage">HTML DOM の概念と利用方法</h2>
+
+<p>この記事では、HTML DOM の中で HTML 要素に関係する部分に焦点を当てます。{{DOMxRef("HTML_Drag_and_Drop_API", "ドラッグアンドドロップ", "", "1")}}、{{DOMxRef("WebSockets_API", "ウェブソケット", "", "1")}}、{{DOMxRef("Web_Storage_API", "ウェブストレージ", "", "1")}}などの他の分野についての議論は、それらの API のドキュメントを参照してください。</p>
+
+<h3 id="Structure_of_an_HTML_document" name="Structure_of_an_HTML_document">HTML 文書の構造</h3>
+
+<p>Document Object Model ({{Glossary("DOM")}}) は、{{domxref("document", "文書", "", 1)}}の構造を記述する構造で、それぞれの文書は {{domxref("Document")}} インターフェイスのインスタンスで表現されます。文書は<strong>ノード</strong>の階層ツリーで構成され、ノードは文書内の単一のオブジェクト (要素やテキストノードなど) を表す基本レコードです。</p>
+
+<p>ノードは厳密に組織化することができ、他のノードをグループ化する手段を提供したり、階層構造を構築するためのポイントを提供したりします。各ノードは、そのノードに関する情報を取得するためのプロパティと、DOM 内でノードを作成、削除、整理するためのメソッドを提供する {{domxref("Node")}} インタフェースに基づいています。</p>
+
+<p>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 the {{domxref("Element")}} interface. An <code>Element</code> object instance represents a single element in a document created using either HTML or an {{glossary("XML")}} vocabulary such as {{glossary("SVG")}}.</p>
+
+<p>For example, consider a document with two elements, one of which has two more elements nested inside it:</p>
+
+<p><img alt="Structure of a document with elements inside a document in a window" src="https://mdn.mozillademos.org/files/16587/dom-structure.svg" style="display: block; height: 379px; margin: 0 auto; width: 291px;"></p>
+
+<p>While the {{domxref("Document")}} interface is defined as part of the {{DOMxRef("Document_Object_Model", "DOM", "", "1")}} 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.</p>
+
+<p>Among the things added to <code>Document</code> by the HTML standard are:</p>
+
+<ul>
+ <li>Support for accessing various information provided by the {{Glossary("HTTP")}} headers when loading the page, such as the {{DOMxRef("Document/location", "location", "", "1")}} from which the document was loaded, {{DOMxRef("Document/cookie", "cookies", "", "1")}}, {{DOMxRef("Document/lastModified", "modification date", "", "1")}}, {{DOMxRef("Document/referrer", "referring site", "", "1")}}, and so forth.</li>
+ <li>Access to lists of elements in the document's {{HTMLElement("head")}} block and {{DOMxRef("Document/body", "body", "", "1")}}, as well as lists of the {{DOMxRef("Document/images", "images", "", "1")}}, {{DOMxRef("Document/links", "links", "", "1")}}, {{DOMxRef("Document/scripts", "scripts", "", "1")}}, etc. contained in the document.</li>
+ <li>Support for interacting with the user by examining {{DOMxRef("Document/hasFocus", "focus", "", "1")}} and by executing commands on <a href="/ja/docs/Web/HTML/Global_attributes/contenteditable">editable content</a>.</li>
+ <li>Event handlers for document {{DOMxRef("GlobalEventHandlers", "events defined by the HTML standard", "", "1")}} to allow access to {{DOMxRef("MouseEvent", "mouse", "", "1")}} and {{DOMxRef("KeyboardEvent", "keyboard", "", "1")}} events, {{DOMxRef("HTML_Drag_and_Drop_API", "drag and drop", "", "1")}}, {{DOMxRef("HTMLMediaElement", "media control", "", "1")}}, and more.</li>
+ <li>Event handlers for events that can be delivered to both elements and documents; these presently include only {{DOMxRef("HTMLElement/oncopy", "copy", "", "1")}}, {{DOMxRef("HTMLElement/oncut", "cut", "", "1")}}, and {{DOMxRef("HTMLElement/onpaste", "paste", "", "1")}} actions.</li>
+</ul>
+
+<h3 id="HTML_element_interfaces" name="HTML_element_interfaces">HTML 要素のインターフェイス</h3>
+
+<p>The <code>Element</code> interface has been further adapted to represent HTML elements specifically by introducing the {{domxref("HTMLElement")}} interface, which all more specific HTML element classes inherit from. This expands the <code>Element</code> class to add HTML-specific general features to the element nodes. Properties added by <code>HTMLElement</code> include for example {{domxref("HTMLElement.hidden", "hidden")}} and {{domxref("HTMLElement.innerText", "innerText")}}. <code>HTMLElement</code> also adds all the {{DOMxRef("GlobalEventHandlers", "global event handlers", "", "1")}}.</p>
+
+<p>An {{Glossary("HTML")}} document is a DOM tree in which each of the nodes is an HTML element, represented by the {{domxref("HTMLElement")}} interface. The <code>HTMLElement</code> class, in turn, implements <code>Node</code>, so every element is also a node (but not the other way around). This way, the structural features implemented by the {{domxref("Node")}} interface are also available to HTML elements, allowing them to be nested within each other, created and deleted, moved around, and so forth.</p>
+
+<p>The <code>HTMLElement</code> 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.</p>
+
+<p>In order to expand upon the functionality of the core <code>HTMLElement</code> interface to provide the features needed by a specific element, the <code>HTMLElement</code> class is subclassed to add the needed properties and methods. For example, the {{HTMLElement("canvas")}} element is represented by an object of type {{domxref("HTMLCanvasElement")}}. <code>HTMLCanvasElement</code> augments the <code>HTMLElement</code> type by adding properties such as {{domxref("HTMLCanvasElement.height", "height")}} and methods like {{domxref("HTMLCanvasElement.getContext", "getContext()")}} to provide canvas-specific features.</p>
+
+<p>The overall inheritance for HTML element classes looks like this:</p>
+
+<p><img alt="Hierarchy of interfaces for HTML elements" src="https://mdn.mozillademos.org/files/16596/html-dom-hierarchy.svg" style="display: block; height: 565px; margin: 0 auto; width: 661px;"></p>
+
+<p>As such, an element inherits the properties and methods of all of its ancestors. For example, consider a {{HTMLElement("a")}} element, which is represented in the DOM by an object of type {{domxref("HTMLAnchorElement")}}. The element, then, includes the anchor-specific properties and methods described in that class's documentation, but also those defined by {{domxref("HTMLElement")}} and {{domxref("Element")}}, as well as from {{domxref("Node")}} and, finally, {{domxref("EventTarget")}}.</p>
+
+<p>Each level defines a key aspect of the utility of the element. From <code>Node</code>, 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 from <code>EventTarget</code>: the ability to receive and handle events such as mouse clicks, play and pause events, and so forth.</p>
+
+<p>There are elements that share commonalities and thus have an additional intermediary type. For example, the {{HTMLElement("audio")}} and {{HTMLElement("video")}} elements both present audiovisual media. The corresponding types, {{domxref("HTMLAudioElement")}} and {{domxref("HTMLVideoElement")}}, are both based upon the common type {{domxref("HTMLMediaElement")}}, which in turn is based upon {{domxref("HTMLElement")}} and so forth. <code>HTMLMediaElement</code> defines the methods and properties held in common between audio and video elements.</p>
+
+<p>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 the {{DOMxRef("Document_Object_Model", "DOM", "", "1")}}, see {{DOMxRef("Document_Object_Model/Introduction", "Introduction to the DOM", "", "1")}}.</p>
+
+<h2 id="HTML_DOM_target_audience" name="HTML_DOM_target_audience">HTML DOM の対象読者</h2>
+
+<p>The features exposed by the HTML DOM are among the most commonly-used APIs in the web developer's arsenal. All but the most simple web applications will use some features of the HTML DOM.</p>
+
+<h2 id="HTML_DOM_API_interfaces" name="HTML_DOM_API_interfaces">HTML DOM API のインターフェイス</h2>
+
+<p>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.</p>
+
+<h3 id="HTML_element_interfaces_2" name="HTML_element_interfaces_2">HTML 要素のインターフェイス</h3>
+
+<p>These interfaces represent specific HTML elements (or sets of related elements which have the same properties and methods associated with them).</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLAnchorElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLAreaElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLAudioElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLBRElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLBaseElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLBodyElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLButtonElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLCanvasElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLDListElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLDataElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLDataListElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLDetailsElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLDialogElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLDirectoryElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLDivElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLEmbedElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLFieldSetElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLFormElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLHRElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLHeadElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLHeadingElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLHtmlElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLIFrameElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLImageElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLInputElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLLIElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLLabelElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLLegendElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLLinkElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLMapElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLMediaElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLMenuElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLMetaElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLMeterElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLModElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLOListElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLObjectElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLOptGroupElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLOptionElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLOutputElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLParagraphElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLParamElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLPictureElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLPreElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLProgressElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLQuoteElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLScriptElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLSelectElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLSlotElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLSourceElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLSpanElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLStyleElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTableCaptionElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTableCellElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTableColElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTableElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTableRowElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTableSectionElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTemplateElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTextAreaElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTimeElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTitleElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLTrackElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLUListElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLUnknownElement")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLVideoElement")}}</span></span></li>
+</ul>
+</div>
+
+<h4 id="Deprecated_HTML_Element_Interfaces" name="Deprecated_HTML_Element_Interfaces">非推奨の HTML 要素のインターフェイス</h4>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLMarqueeElement")}} {{deprecated_inline}}</span></span></li>
+</ul>
+</div>
+
+<h4 id="Obsolete_HTML_Element_Interfaces" name="Obsolete_HTML_Element_Interfaces">廃止された HTML 要素のインターフェイス</h4>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLBaseFontElement")}} {{obsolete_inline}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLFontElement")}} {{obsolete_inline}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLFrameElement")}} {{obsolete_inline}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLFrameSetElement")}} {{obsolete_inline}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLIsIndexElement")}} {{obsolete_inline}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLMenuItemElement")}} {{obsolete_inline}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Web_app_and_browser_integration_interfaces" name="Web_app_and_browser_integration_interfaces">ウェブアプリとブラウザーの統合インターフェイス</h3>
+
+<p>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.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("BarProp")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("Navigator")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("Window")}}</span></span></li>
+</ul>
+</div>
+
+<h4 id="Deprecated_web_app_and_browser_integration_interfaces" name="Deprecated_web_app_and_browser_integration_interfaces">非推奨のウェブアプリとブラウザーの統合インターフェイス</h4>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("External")}} {{deprecated_inline}}</span></span></li>
+</ul>
+</div>
+
+<h4 id="Obsolete_web_app_and_browser_integration_interfaces" name="Obsolete_web_app_and_browser_integration_interfaces">廃止されたウェブアプリとブラウザーの統合インターフェイス</h4>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("ApplicationCache")}} {{obsolete_inline}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("Plugin")}} {{obsolete_inline}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("PluginArray")}} {{obsolete_inline}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Form_support_interfaces" name="Form_support_interfaces">フォーム対応インターフェイス</h3>
+
+<p>These interfaces provide structure and functionality required by the elements used to create and manage forms, including the {{HTMLElement("form")}} and {{HTMLElement("input")}} elements.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("FormDataEvent")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLFormControlsCollection")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLOptionsCollection")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("RadioNodeList")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("ValidityState")}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Canvas_and_image_interfaces" name="Canvas_and_image_interfaces">キャンバスと画像のインターフェイス</h3>
+
+<p>These interfaces represent objects used by the Canvas API as well as the {{HTMLElement("img")}} element and {{HTMLElement("picture")}} elements.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("CanvasGradient")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("CanvasPattern")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("CanvasRenderingContext2D")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("ImageBitmap")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("ImageBitmapRenderingContext")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("ImageData")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("OffscreenCanvas")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("OffscreenCanvasRenderingContext2D")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("Path2D")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("TextMetrics")}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Media_interfaces" name="Media_interfaces">メディアインターフェイス</h3>
+
+<p>The media interfaces provide HTML access to the contents of the media elements: {{HTMLElement("audio")}} and {{HTMLElement("video")}}.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("AudioTrack")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("AudioTrackList")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("MediaError")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("TextTrack")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("TextTrackCue")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("TextTrackCueList")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("TextTrackList")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("TimeRanges")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("TrackEvent")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("VideoTrack")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("VideoTrackList")}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Drag_and_drop_interfaces" name="Drag_and_drop_interfaces">ドラッグ＆ドロップインターフェイス</h3>
+
+<p>These interfaces are used by the {{DOMxRef("HTML_Drag_and_Drop_API", "", "", "1")}} to represent individual draggable (or dragged) items, groups of dragged or draggable items, and to handle the drag and drop process.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("DataTransfer")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("DataTransferItem")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("DataTransferItemList")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("DragEvent")}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Page_history_interfaces" name="Page_history_interfaces">ページ履歴インターフェイス</h3>
+
+<p>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.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("BeforeUnloadEvent")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HashChangeEvent")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("History")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("Location")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("PageTransitionEvent")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("PopStateEvent")}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Web_Components_interfaces" name="Web_Components_interfaces">ウェブコンポーネントインターフェイス</h3>
+
+<p>These interfaces are used by the <a href="/ja/docs/Web/Web_Components">Web Components API</a> to create and manage the available <a href="/ja/docs/Web/Web_Components/Using_custom_elements">custom elements</a>.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("CustomElementRegistry")}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Miscellaneous_and_supporting_interfaces" name="Miscellaneous_and_supporting_interfaces">その他および補助インターフェイス</h3>
+
+<p>These supporting object types are used in a variety of ways in the HTML DOM API. In addition, {{domxref("PromiseRejectionEvent")}} represents the event delivered when a {{Glossary("JavaScript")}} {{jsxref("Promise")}} is rejected.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("DOMStringList")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("DOMStringMap")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("ErrorEvent")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("HTMLAllCollection")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("MimeType")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("MimeTypeArray")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("PromiseRejectionEvent")}}</span></span></li>
+</ul>
+</div>
+
+<h3 id="Interfaces_belonging_to_other_APIs" name="Interfaces_belonging_to_other_APIs">他の API に所属するインターフェイス</h3>
+
+<p>Several interfaces are technically defined in the HTML specification while actually being part of other APIs.</p>
+
+<h4 id="Web_storage_interfaces" name="Web_storage_interfaces">ウェブストレージインターフェイス</h4>
+
+<p>The {{DOMxRef("Web_Storage_API", "", "", "1")}} provides the ability for web sites to store data either temporarily or permanently on the user's device for later re-use.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("Storage")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("StorageEvent")}}</span></span></li>
+</ul>
+</div>
+
+<h4 id="Web_Workers_interfaces" name="Web_Workers_interfaces">ウェブワーカーインターフェイス</h4>
+
+<p>These interfaces are used by the {{DOMxRef("Web_Workers_API", "", "", "1")}} both to establish the ability for workers to interact with an app and its content, but also to support messaging between windows or apps.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("BroadcastChannel")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("DedicatedWorkerGlobalScope")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("MessageChannel")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("MessageEvent")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("MessagePort")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("SharedWorker")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("SharedWorkerGlobalScope")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("Worker")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("WorkerGlobalScope")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("WorkerLocation")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("WorkerNavigator ")}}</span></span></li>
+</ul>
+</div>
+
+<h4 id="WebSocket_interfaces" name="WebSocket_interfaces">WebSocket インターフェイス</h4>
+
+<p>These interfaces, defined by the HTML specification, are used by the {{DOMxRef("WebSockets_API", "", "", "1")}}.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("CloseEvent")}}</span></span></li>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("WebSocket")}}</span></span></li>
+</ul>
+</div>
+
+<h4 id="Server-sent_events_interfaces" name="Server-sent_events_interfaces">Server-sent event インターフェイス</h4>
+
+<p>The {{domxref("EventSource")}} interface represents the source which sent or is sending {{DOMxRef("Server-sent_events", "server-sent events", "", "1")}}.</p>
+
+<div class="index">
+<ul>
+ <li><span class="indexListRow"><span class="indexListTerm">{{DOMxRef("EventSource")}}</span></span></li>
+</ul>
+</div>
+
+<h2 id="Examples" name="Examples">例</h2>
+
+<p>In this example, an {{HTMLElement("input")}} element's {{domxref("HTMLInputElement.input_event", "input")}} event is monitored in order to update the state of a form's "submit" button based on whether or not a given field currently has a value.</p>
+
+<h4 id="JavaScript" name="JavaScript">JavaScript</h4>
+
+<pre class="brush: js notranslate">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 =&gt; {
+  const elem = event.target;
+  const valid = elem.value.length != 0;
+
+  if (valid &amp;&amp; sendButton.disabled) {
+    sendButton.disabled = false;
+  } else if (!valid &amp;&amp; !sendButton.disabled) {
+    sendButton.disabled = true;
+  }
+});</pre>
+
+<p>This code uses the {{domxref("Document")}} interface's {{domxref("Document.getElementById", "getElementById()")}} method to get the DOM object representing the {{HTMLElement("input")}} elements whose IDs are <code>userName</code> and <code>sendButton</code>. With these, we can access the properties and methods that provide information about and grant control over these elements.</p>
+
+<p>The {{domxref("HTMLInputElement")}} object for the "Send" button's {{domxref("HTMLInputElement.disabled", "disabled")}} property is set to <code>true</code>, 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 the {{domxref("HTMLElement.focus", "focus()")}} method it inherits from {{domxref("HTMLElement")}}.</p>
+
+<p>Then {{domxref("EventTarget.addEventListener", "addEventListener()")}} is called to add a handler for the <code>input</code> 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.</p>
+
+<p>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.</p>
+
+<h4 id="HTML" name="HTML">HTML</h4>
+
+<p>The HTML for the form looks like this:</p>
+
+<pre class="brush: html notranslate">&lt;p&gt;Please provide the information below. Items marked with "*" are required.&lt;/p&gt;
+&lt;form action="" method="get"&gt;
+  &lt;p&gt;
+    &lt;label for="userName" required&gt;Your name:&lt;/label&gt;
+    &lt;input type="text" id="userName"&gt; (*)
+  &lt;/p&gt;
+  &lt;p&gt;
+    &lt;label for="email"&gt;Email:&lt;/label&gt;
+    &lt;input type="email" id="userEmail"&gt;
+  &lt;/p&gt;
+  &lt;input type="submit" value="Send" id="sendButton"&gt;
+&lt;/form&gt;
+</pre>
+
+<h4 id="Result" name="Result">結果</h4>
+
+<p>{{EmbedLiveSample("Examples", 640, 300)}}</p>
+
+<h2 id="Specifications" name="Specifications">仕様書</h2>
+
+<table class="standard-table">
+ <thead>
+  <tr>
+   <th scope="col">仕様書</th>
+   <th scope="col">状態</th>
+   <th scope="col">備考</th>
+  </tr>
+ </thead>
+ <tbody>
+  <tr>
+   <td>{{SpecName('HTML WHATWG')}}</td>
+   <td>{{Spec2('HTML WHATWG')}}</td>
+   <td>WHATWG HTML Specification</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('HTML5 W3C')}}</td>
+   <td>{{Spec2('HTML5 W3C')}}</td>
+   <td>No change from {{SpecName("DOM2 HTML")}}</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('DOM2 HTML')}}</td>
+   <td>{{Spec2('DOM2 HTML')}}</td>
+   <td>No change from {{SpecName("DOM1")}}.</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('DOM1')}}</td>
+   <td>{{Spec2('DOM1')}}</td>
+   <td>初回定義</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Browser_compatibility" name="Browser_compatibility">ブラウザーの互換性</h2>
+
+<div>
+<div class="hidden">このページの互換性一覧表は構造化データから生成されています。データに協力していただけるのであれば、 <a class="external" href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> をチェックアウトしてプルリクエストを送信してください。</div>
+
+<p>{{Compat("api.HTMLElement")}}</p>
+</div>
+
+<h2 id="See_also" name="See_also">関連情報</h2>
+
+<dl>
+ <dt>リファレンス</dt>
+ <dd>
+ <ul>
+  <li><a href="/ja/docs/Web/HTML/Element">HTML 要素リファレンス</a></li>
+  <li><a href="/ja/docs/Web/HTML/Attributes">HTML 属性リファレンス</a></li>
+  <li>{{DOMxRef("Document_Object_Model", "Document Object Model (DOM)", "", "1")}} reference</li>
+ </ul>
+ </dd>
+ <dt>ガイド</dt>
+ <dd>
+ <ul>
+  <li>
+   <p><a href="/ja/docs/Learn/JavaScript/Client-side_web_APIs/Manipulating_documents">文書の操作</a>: DOM を操作するための初心者向けガイドです。</p>
+  </li>
+ </ul>
+ </dd>
+</dl>
diff --git a/files/ja/web/api/html_dom_api/microtask_guide/index.html b/files/ja/web/api/html_dom_api/microtask_guide/index.html
new file mode 100644
index 0000000000..3c7e68152e
--- /dev/null
+++ b/files/ja/web/api/html_dom_api/microtask_guide/index.html
@@ -0,0 +1,326 @@
+---
+title: Using microtasks in JavaScript with queueMicrotask()
+slug: Web/API/HTML_DOM_API/Microtask_guide
+tags:
+  - API
+  - Batch
+  - Guide
+  - HTML DOM
+  - JavaScript
+  - Microtask
+  - Queue
+  - Reference
+  - ServiceWorker
+  - SharedWorker
+  - Window
+  - Worker
+  - asynchronous
+  - queueMicrotask
+translation_of: Web/API/HTML_DOM_API/Microtask_guide
+---
+<p>{{APIRef("HTML DOM")}}</p>
+
+<p><span class="seoSummary"><strong>マイクロタスク</strong> は、それを作成する関数/プログラムが終了した後、JavaScript実行スタックが空な場合のみに、スクリプトの実行環境を動かしている{{Glossary("user agent")}}が使っているイベントループに制御が戻る前に実行される短い関数です。</span>このイベントループはブラウザーのメインのイベントループと、<a href="/ja/docs/Web/API/Web_Workers_API">web worker</a>が動かしているイベントループのいずれかです。 これにより、ある関数が他のスクリプトの実行に干渉するリスクを除外して実行できます。またマイクロタスクが取ったアクションにユーザーエージェントが反応するよりも前に、マイクロタスクを確実に実行させることもできます。</p>
+
+<p>JavaScript <a href="/ja/docs/Web/JavaScript/Reference/Global_Objects/Promise">promises</a> and the <a href="//en-US/docs/Web/API/Mutation_Observer_API">Mutation Observer API</a> both use the microtask queue to run their callbacks, but there are other times when the ability to defer work until the current event loop pass is wrapping up. In order to allow microtasks to be used by third-party libraries, frameworks, and polyfills, the {{domxref("WindowOrWorkerGlobalScope.queueMicrotask", "queueMicrotask()")}} method is exposed on the {{domxref("Window")}} and {{domxref("Worker")}} interfaces through the {{domxref("WindowOrWorkerGlobalScope")}} mixin.</p>
+
+<h2 id="Tasks_vs_microtasks" name="Tasks_vs_microtasks">タスクとマイクロタスクの比較</h2>
+
+<p>To properly discuss microtasks, it's first useful to know what a JavaScript task is and how microtasks differ from tasks. This is a quick, simplified explanation, but if you would like more details, you can read the information in the article <a href="/ja/docs/Web/API/HTML_DOM_API/Microtask_guide/In_depth">In depth: Microtasks and the JavaScript runtime environment</a>.</p>
+
+<h3 id="Tasks" name="Tasks">タスク</h3>
+
+<p>A <strong>task</strong> is any JavaScript code which is scheduled to be run by the standard mechanisms such as initially starting to run a program, an event callback being run, or an interval or timeout being fired. These all get scheduled on the <strong>task queue</strong>.</p>
+
+<p>Tasks get added to the task queue when:</p>
+
+<ul>
+ <li>A new JavaScript program or subprogram is executed (such as from a console, or by running the code in a {{HTMLElement("script")}} element) directly.</li>
+ <li>An event fires, adding the event's callback function to the task queue.</li>
+ <li>A timeout or interval created with {{domxref("WindowOrWorkerGlobalScope.setTimeout", "setTimeout()")}} or {{domxref("WindowOrWorkerGlobalScope.setInterval", "setInterval()")}} is reached, causing the corresponding callback to be added to the task queue.</li>
+</ul>
+
+<p>The event loop driving your code handles these tasks one after another, in the order in which they were enqueued. Only tasks which were <em>already in the task queue</em> when the event loop pass began will be executed during the current iteration. The rest will have to wait until the following iteration.</p>
+
+<h3 id="Microtasks" name="Microtasks">マイクロタスク</h3>
+
+<p>At first the difference between microtasks and tasks seems minor. And they are similar; both are made up of JavaScript code which gets placed on a queue and run at an appropriate time. However, whereas the event loop runs only the tasks present on the queue when the iteration began, one after another, it handles the microtask queue very differently.</p>
+
+<p>There are two key differences.</p>
+
+<p>First, each time a task exits, the event loop checks to see if the task is returning control to other JavaScript code. If not, it runs all of the microtasks in the microtask queue. The microtask queue is, then, processed multiple times per iteration of the event loop, including after handling events and other callbacks.</p>
+
+<p>Second, if a microtask adds more microtasks to the queue by calling {{domxref("WindowOrWorkerGlobalScope.queueMicrotask", "queueMicrotask()")}}, those newly-added microtasks <em>execute before the next task is run</em>. That's because the event loop will keep calling microtasks until there are none left in the queue, even if more keep getting added.</p>
+
+<div class="blockIndicator warning">
+<p><strong>Warning:</strong> Since microtasks can themselves enqueue more microtasks, and the event loop continues processing microtasks until the queue is empty, there's a real risk of getting the event loop endlessly processing microtasks. Be cautious with how you go about recursively adding microtasks.</p>
+</div>
+
+<h2 id="Using_microtasks" name="Using_microtasks">マイクロタスクを使用する</h2>
+
+<p>Before getting farther into this, it's important to note again that most developers won't use microtasks much, if at all. They're a highly specialized feature of modern browser-based JavaScript development, allowing you to schedule code to jump in front of other things in the long set of things waiting to happen on the user's computer. Abusing this capability will lead to performance problems.</p>
+
+<h3 id="Enqueueing_microtasks" name="Enqueueing_microtasks">マイクロタスクをキューに入れる</h3>
+
+<p>As such, you should typically use microtasks only when there's no other solution, or when creating frameworks or libraries that need to use microtasks in order to create the functionality they're implementing. While there have been tricks available that made it possible to enqueue microtasks in the past (such as by creating a promise that resolves immediately), the addition of  the {{domxref("WindowOrWorkerGlobalScope.queueMicrotask", "queueMicrotask()")}} method adds a standard way to introduce a microtask safely and without tricks.</p>
+
+<p>By introducing <code>queueMicrotask()</code>, the quirks that arise when sneaking in using promises to create microtasks can be avoided. For instance, when using promises to create microtasks, exceptions thrown by the callback are reported as rejected promises rather than being reported as standard exceptions. Also, creating and destroying promises takes additional overhead both in terms of time and memory that a function which properly enqueues microtasks avoids.</p>
+
+<p>Simply pass the JavaScript {{jsxref("Function")}} to call while the context is handling microtasks into the <code>queueMicrotask()</code> method, which is exposed on the global context as defined by either the {{domxref("Window")}} or {{domxref("Worker")}} interface, depending on the current execution context.</p>
+
+<pre class="brush: js">queueMicrotask(() =&gt; {
+  /* code to run in the microtask here */
+});
+</pre>
+
+<p>The microtask function itself takes no parameters, and does not return a value.</p>
+
+<h3 id="When_to_use_microtasks" name="When_to_use_microtasks">マイクロタスクを使うべきとき</h3>
+
+<p>In this section, we'll take a look at scenarios in which microtasks are particularly useful. Generally, it's about capturing or checking results, or performing cleanup, after the main body of a JavaScript execution context exits, but before any event handlers, timeouts and intervals, or other callbacks are processed.</p>
+
+<p>When is that useful?</p>
+
+<p>The main reason to use microtasks is simply that: to ensure consistent ordering of tasks, even when results or data is available synchronously, but while simultaneously reducing the risk of user-discernible delays in operations.</p>
+
+<h4 id="Ensuring_ordering_on_conditional_use_of_promises" name="Ensuring_ordering_on_conditional_use_of_promises">Promiseの条件付き使用の順番を確定させる</h4>
+
+<p>実行順序が常に一貫するよう保証するためにマイクロタスクを使用できる状況として、Promiseが単一の <code>if...else</code> 文 (や他の条件文)の句の中にあって、他の句の内にないときです。次のコードを考えてみます:</p>
+
+<pre class="brush: js">customElement.prototype.getData = url =&gt; {
+  if (this.cache[url]) {
+    this.data = this.cache[url];
+    this.dispatchEvent(new Event("load"));
+  } else {
+    fetch(url).then(result =&gt; result.arrayBuffer()).then(data =&gt; {
+      this.cache[url] = data;
+      this.data = data;
+      this.dispatchEvent(new Event("load"));
+    )};
+  }
+};</pre>
+
+<p>ここで入ってきた問題は、<code>if...else</code> 文 (画像がキャッシュ内で利用できる場合) の分岐内でタスクを使っているが、<code>else</code> 句でPromiseがある場合、命令の順序が変わる状況になります; 例えば、次のように。</p>
+
+<pre class="brush: js">element.addEventListener("load", () =&gt; console.log("Loaded data"));
+console.log("Fetching data...");
+element.getData();
+console.log("Data fetched");
+</pre>
+
+<p>このコードを行の中で2回実行すると、次の表の結果になります:</p>
+
+<table class="standard-table">
+ <caption>データがキャッシュされていない (左) ときと、データがキャッシュされているときの結果</caption>
+ <thead>
+  <tr>
+   <th scope="col">データはキャッシュされていない</th>
+   <th scope="col">データはキャッシュされている</th>
+  </tr>
+ </thead>
+ <tbody>
+  <tr>
+   <td>
+    <pre>
+Fetching data
+Data fetched
+Loaded data
+</pre>
+   </td>
+   <td>
+    <pre>
+Fetching data
+Loaded data
+Data fetched
+</pre>
+   </td>
+  </tr>
+ </tbody>
+</table>
+
+<p>もっと悪いことに、このコードが実行完了となるまでに、要素の <code>data</code> プロパティは時々セットされたり、されなかったりもします。</p>
+
+<p>これらの命令の順序を一貫させるために、マイクロタスクを <code>if</code> 句の中で使って、2つの句のバランスを取ることができます:</p>
+
+<pre class="brush: js">customElement.prototype.getData = url =&gt; {
+  if (thiscache[url]) {
+    queueMicrotask(() =&gt; {
+      this.data = this.cache[url];
+      this.dispatchEvent(new Event("load"));
+    });
+  } else {
+    fetch(url).then(result =&gt; result.arrayBuffer()).then(data =&gt; {
+      this.cache[url] = data;
+      this.data = data;
+      this.dispatchEvent(new Event("load"));
+    )};
+  }
+};</pre>
+
+<p>両方の状況でマイクロタスク内で <code>data</code> をセットして <code>load</code> イベントを発火させる (<code>if</code> 句では <code>queueMicrotask()</code>を使い <code>else</code> 句では{{domxref("WindowOrWorkerGlobalScope.fetch", "fetch()")}} を使う) ことで、句ごとにバランスを取っています。</p>
+
+<h4 id="Batching_operations" name="Batching_operations">バッチオペレーション</h4>
+
+<p>You can also use microtasks to collect multiple requests from various sources into a single batch, avoiding the possible overhead involved with multiple calls to handle the same kind of work.</p>
+
+<p>The snippet below creates a function that batches multiple messages into an array, using a microtask to send them as a single object when the context exits.</p>
+
+<pre class="brush: js">const messageQueue = [];
+
+let sendMessage = message =&gt; {
+  messageQueue.push(message);
+
+  if (messageQueue.length === 1) {
+    queueMicrotask(() =&gt; {
+      const json = JSON.stringify(messageQueue);
+      messageQueue.length = 0;
+      fetch("url-of-receiver", json);
+    });
+  }
+};
+</pre>
+
+<p>When <code>sendMessage()</code> gets called, the specified message is first pushed onto the message queue array. Then things get interesting.</p>
+
+<p>If the message we just added to the array is the first one, we enqueue a microtask that will send a batch. The microtask will execute, as always, when the JavaScript execution path reaches the top level, just before running callbacks. That means that any further calls to <code>sendMessage()</code> made in the interim will push their messages onto the message queue, but because of the array length check before adding a microtask, no new microtask is enqueued.</p>
+
+<p>When the microtask runs, then, it has an array of potentially many messages waiting for it. It starts by encoding it as JSON using the {{jsxref("JSON.stringify()")}} method. After that, the array's contents aren't needed anymore, so we empty the <code>messageQueue</code> array. Finally, we use the {{domxref("WindowOrWorkerGlobalScope.fetch", "fetch()")}} method to send the JSON string to the server.</p>
+
+<p>This lets every call to <code>sendMessage()</code> made during the same iteration of the event loop add their messages to the same <code>fetch()</code> operation, without potentially having other tasks such as timeouts or the like delay the transmission.</p>
+
+<p>The server will receive the JSON string, then will presumably decode it and process the messages it finds in the resulting array.</p>
+
+<h2 id="Examples" name="Examples">例</h2>
+
+<h3 id="Simple_microtask_example" name="Simple_microtask_example">簡単なマイクロタスクの例</h3>
+
+<p>In this simple example, we see that enqueueing a microtask causes the microtask's callback to run after the body of this top-level script is done running.</p>
+
+<div class="hidden">
+<h4 id="HTML" name="HTML">HTML</h4>
+
+<pre class="brush: html">&lt;pre id="log"&gt;
+&lt;/pre&gt;</pre>
+</div>
+
+<h4 id="JavaScript" name="JavaScript">JavaScript</h4>
+
+<div class="hidden">
+<p>The code below is used to log the output.</p>
+
+<pre class="brush: js">let logElem = document.getElementById("log");
+let log = s =&gt; logElem.innerHTML += s + "&lt;br&gt;";</pre>
+</div>
+
+<p>In the following code, we see a call to {{domxref("WindowOrWorkerGlobalScope.queueMicrotask", "queueMicrotask()")}} used to schedule a microtask to run. This call is bracketed by calls to <code>log()</code>, a custom function that simply outputs text to the screen.</p>
+
+<pre class="brush: js">log("Before enqueueing the microtask");
+queueMicrotask(() =&gt; {
+  log("The microtask has run.")
+});
+log("After enqueueing the microtask");</pre>
+
+<h4 id="Result" name="Result">結果</h4>
+
+<p>{{EmbedLiveSample("Simple_microtask_example", 640, 80)}}</p>
+
+<h3 id="Timeout_and_microtask_example" name="Timeout_and_microtask_example">Timeoutとマイクロタスクの例</h3>
+
+<p>In this example, a timeout is scheduled to fire after zero milliseconds (or "as soon as possible"). This demonstrates the difference between what "as soon as possible" means when scheduling a new task (such as by using <code>setTimeout()</code>) versus using a microtask.</p>
+
+<div class="hidden">
+<h4 id="HTML_2" name="HTML_2">HTML</h4>
+
+<pre class="brush: html">&lt;pre id="log"&gt;
+&lt;/pre&gt;</pre>
+</div>
+
+<h4 id="JavaScript_2" name="JavaScript_2">JavaScript</h4>
+
+<div class="hidden">
+<p>The code below is used to log the output.</p>
+
+<pre class="brush: js">let logElem = document.getElementById("log");
+let log = s =&gt; logElem.innerHTML += s + "&lt;br&gt;";</pre>
+</div>
+
+<p>In the following code, we see a call to {{domxref("WindowOrWorkerGlobalScope.queueMicrotask", "queueMicrotask()")}} used to schedule a microtask to run. This call is bracketed by calls to <code>log()</code>, a custom function that simply outputs text to the screen.</p>
+
+<p>The code below schedules a timeout to occur in zero milliseconds, then enqueues a microtask. This is bracketed by calls to <code>log()</code> to output additional messages.</p>
+
+<pre class="brush: js">let callback = () =&gt; log("Regular timeout callback has run");
+
+let urgentCallback = () =&gt; log("*** Oh noes! An urgent callback has run!");
+
+log("Main program started");
+setTimeout(callback, 0);
+queueMicrotask(urgentCallback);
+log("Main program exiting");</pre>
+
+<h4 id="Result_2" name="Result_2">結果</h4>
+
+<p>{{EmbedLiveSample("Timeout_and_microtask_example", 640, 100)}}</p>
+
+<p>Note that the output logged from the main program body appears first, followed by the output from the microtask, followed by the timeout's callback. That's because when the task that's handling the execution of the main program exits, the microtask queue gets processed before the task queue on which the timeout callback is located. Remembering that tasks and microtasks are kept on separate queues, and that microtasks run first will help keep this straight.</p>
+
+<h3 id="Microtask_from_a_function" name="Microtask_from_a_function">関数からのマイクロタスク</h3>
+
+<p>This example expands slightly on the previous one by adding a function that does some work. This function uses <code>queueMicrotask()</code> to schedule a microtask. The important thing to take away from this one is that the microtask isn't processed when the function exits, but when the main program exits.</p>
+
+<div class="hidden">
+<h4 id="HTML_3" name="HTML_3">HTML</h4>
+
+<pre class="brush: html">&lt;pre id="log"&gt;
+&lt;/pre&gt;</pre>
+</div>
+
+<h4 id="JavaScript_3" name="JavaScript_3">JavaScript</h4>
+
+<div class="hidden">
+<p>The code below is used to log the output.</p>
+
+<pre class="brush: js">let logElem = document.getElementById("log");
+let log = s =&gt; logElem.innerHTML += s + "&lt;br&gt;";</pre>
+</div>
+
+<p>The main program code follows. The <code>doWork()</code> function here calls <code>queueMicrotask()</code>, yet the microtask still doesn't fire until the entire program exits, since that's when the task exits and there's nothing else on the execution stack.</p>
+
+<pre class="brush: js">let callback = () =&gt; log("Regular timeout callback has run");
+
+let urgentCallback = () =&gt; log("*** Oh noes! An urgent callback has run!");
+
+let doWork = () =&gt; {
+  let result = 1;
+
+  queueMicrotask(urgentCallback);
+
+  for (let i=2; i&lt;=10; i++) {
+    result *= i;
+  }
+  return result;
+};
+
+log("Main program started");
+setTimeout(callback, 0);
+log(`10! equals ${doWork()}`);
+log("Main program exiting");</pre>
+
+<h4 id="Result_3" name="Result_3">結果</h4>
+
+<p>{{EmbedLiveSample("Microtask_from_a_function", 640, 100)}}</p>
+
+<h2 id="See_also" name="See_also">関連情報</h2>
+
+<ul>
+ <li><a href="/ja/docs/Web/API/HTML_DOM_API/Microtask_guide/In_depth">In depth: Microtasks and the JavaScript runtime environment</a></li>
+ <li>{{domxref("WindowOrWorkerGlobalScope.queueMicrotask", "queueMicrotask()")}}</li>
+ <li><a href="/ja/docs/Learn/JavaScript/Asynchronous">Asynchronous JavaScript</a>
+  <ul>
+   <li><a href="/ja/docs/Learn/JavaScript/Asynchronous/Concepts">General asynchronous programming concepts</a></li>
+   <li><a href="/ja/docs/Learn/JavaScript/Asynchronous/Introducing">Introducing asynchronous JavaScript</a></li>
+   <li><a href="/ja/docs/Learn/JavaScript/Asynchronous/Timeouts_and_intervals">Cooperative asynchronous JavaScript: Timeouts and intervals</a></li>
+   <li><a href="/ja/docs/Learn/JavaScript/Asynchronous/Promises">Graceful asynchronous programming with Promises</a></li>
+   <li><a href="/ja/docs/Learn/JavaScript/Asynchronous/Choosing_the_right_approach">Choosing the right approach</a></li>
+  </ul>
+ </li>
+</ul>