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<!DOCTYPE html>
<html lang="en-US"><head>
<meta charset="utf-8" />
<title>W3C DOM4</title>
<link rel="stylesheet" href="style.css" />
<link rel="stylesheet" href="https://www.w3.org/StyleSheets/TR/W3C-WD" /><!--[if lt IE 9]><script src='https://www.w3.org/2008/site/js/html5shiv.js'></script><![endif]--></head>
<body>
<div class="head" role="contentinfo" id="respecHeader">
<p>
<a href="http://www.w3.org/"><img width="72" height="48" src="https://www.w3.org/Icons/w3c_home" alt="W3C" /></a>
</p>
<h1 class="title p-name" id="title" property="dcterms:title">W3C DOM4</h1>
<h2 property="bibo:subtitle" id="subtitle">Snapshot specification for the <a href="http://dom.spec.whatwg.org/">DOM Living Standard</a></h2>
<h2 property="dcterms:issued" datatype="xsd:dateTime" content="2013-11-04T23:00:00.000Z" id="w3c-first-public-working-draft-05-november-2013">W3C First Public Working Draft <time class="dt-published" datetime="2013-11-05">05 November 2013</time></h2>
<dl>
<dt>This version:</dt>
<dd><a class="u-url" href="http://www.w3.org/TR/2013/WD-dom-20131105/">http://www.w3.org/TR/2013/WD-dom-20131105/</a></dd>
<dt>Latest published version:</dt>
<dd><a href="http://www.w3.org/TR/dom/">http://www.w3.org/TR/dom/</a></dd>
<dt>Latest editor's draft:</dt>
<dd><a href="http://w3c.github.io/dom/">http://w3c.github.io/dom/</a></dd>
<dt>Editors:</dt>
<dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><a class="u-url url p-name fn" rel="foaf:homepage" property="foaf:name" content="Anne van Kesteren" href="http://annevankesteren.nl/">Anne van Kesteren</a>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://www.mozilla.org/">Mozilla</a> (Upstream WHATWG version)</span>
</dd>
<dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><span property="foaf:name" class="p-name fn">Aryeh Gregor</span>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://www.mozilla.org/">Mozilla</a> (Upstream WHATWG version)</span>
</dd>
<dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><span property="foaf:name" class="p-name fn">Ms2ger</span>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://www.mozilla.org/">Mozilla</a> (Upstream WHATWG version)</span>
</dd>
<dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><a class="u-url url p-name fn" rel="foaf:homepage" property="foaf:name" content="Alex Russell" href="http://infrequently.org/">Alex Russell</a>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://www.google.com/">Google</a></span>
</dd>
<dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><a class="u-url url p-name fn" rel="foaf:homepage" property="foaf:name" content="Robin Berjon" href="http://berjon.com/">Robin Berjon</a>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://w3.org/">W3C</a></span>
</dd>
</dl>
<p class="copyright">
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> ©
2013
<a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup>
(<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>,
<a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>),
Some Rights Reserved: this document is dual-licensed,
<a href="https://creativecommons.org/licenses/by/3.0/">CC-BY</a> and
<a href="http://www.w3.org/Consortium/Legal/copyright-documents">W3C Document License</a>.
W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and
<a href="http://www.w3.org/Consortium/Legal/2013/copyright-documents-dual.html">document use</a>
rules apply.
</p>
<hr />
</div>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>DOM defines a platform-neutral model for events, promises, and document nodes.
<section id="sotd" class="introductory" typeof="bibo:Chapter" resource="#ref" rel="bibo:Chapter"><h2 aria-level="1" role="heading" id="h2_sotd">Status of This Document</h2>
<p>
<em>This section describes the status of this document at the time of its publication. Other
documents may supersede this document. A list of current W3C publications and the latest revision
of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
index</a> at http://www.w3.org/TR/.</em>
</p>
<p>
This document is published as a snapshot of the
<a href="http://dom.spec.whatwg.org/">DOM Living Standard</a>.
</p>
<p>
This document was published by the <a href="http://www.w3.org/html/wg/">HTML Working Group</a> as a First Public Working Draft.
This document is intended to become a W3C Recommendation.
If you wish to make comments regarding this document, please send them to
<a href="mailto:[email protected]">[email protected]</a>
(<a href="mailto:[email protected]?subject=subscribe">subscribe</a>,
<a href="http://lists.w3.org/Archives/Public/www-dom/">archives</a>).
All comments are welcome.</p>
<p>
Publication as a First Public Working Draft does not imply endorsement by the W3C Membership.
This is a draft document and may be updated, replaced or obsoleted by other documents at
any time. It is inappropriate to cite this document as other than work in progress.
</p>
<p>
This document was produced by a group operating under the
<a id="sotd_patent" about="" rel="w3p:patentRules" href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href="http://www.w3.org/2004/01/pp-impl/40318/status" rel="disclosure">public list of any patent disclosures</a>
made in connection with the deliverables of the group; that page also includes instructions for
disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains
<a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the
information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
6 of the W3C Patent Policy</a>.
</p>
</section><h2 class="no-num no-toc" id="table-of-contents">Table of Contents</h2>
<!--begin-toc-->
<ol class="toc">
<li><a class="no-num" href="#goals">Goals</a></li>
<li><a href="#conformance"><span class="secno">1 </span>Conformance</a>
<ol>
<li><a href="#dependencies"><span class="secno">1.1 </span>Dependencies</a></li>
<li><a href="#extensibility"><span class="secno">1.2 </span>Extensibility</a></li></ol></li>
<li><a href="#terminology"><span class="secno">2 </span>Terminology</a>
<ol>
<li><a href="#trees"><span class="secno">2.1 </span>Trees</a></li>
<li><a href="#strings"><span class="secno">2.2 </span>Strings</a></li>
<li><a href="#ordered-sets"><span class="secno">2.3 </span>Ordered sets</a></li>
<li><a href="#namespaces"><span class="secno">2.4 </span>Namespaces</a></li></ol></li>
<li><a href="#errors"><span class="secno">3 </span>Errors</a>
<ol>
<li><a href="#exception-domexception"><span class="secno">3.1 </span>Exception <code>DOMException</code></a></li>
<li><a href="#interface-domerror"><span class="secno">3.2 </span>Interface <code>DOMError</code></a></li>
<li><a href="#error-names-0"><span class="secno">3.3 </span>Error names</a></li></ol></li>
<li><a href="#promises"><span class="secno">4 </span>Promises</a>
<ol>
<li><a href="#i-promise-you-an-introduction"><span class="secno">4.1 </span>I <code title="">Promise</code> you an introduction</a></li>
<li><a href="#open-issues"><span class="secno">4.2 </span>Open issues</a></li></ol></li>
<li><a href="#events"><span class="secno">5 </span>Events</a>
<ol>
<li><a href="#introduction-to-dom-events"><span class="secno">5.1 </span>Introduction to "DOM Events"</a></li>
<li><a href="#interface-event"><span class="secno">5.2 </span>Interface <code>Event</code></a></li>
<li><a href="#interface-customevent"><span class="secno">5.3 </span>Interface <code>CustomEvent</code></a></li>
<li><a href="#constructing-events"><span class="secno">5.4 </span>Constructing events</a></li>
<li><a href="#defining-event-interfaces"><span class="secno">5.5 </span>Defining event interfaces</a></li>
<li><a href="#interface-eventtarget"><span class="secno">5.6 </span>Interface <code>EventTarget</code></a></li>
<li><a href="#dispatching-events"><span class="secno">5.7 </span>Dispatching events</a></li>
<li><a href="#firing-events"><span class="secno">5.8 </span>Firing events</a></li></ol></li>
<li><a href="#nodes"><span class="secno">6 </span>Nodes</a>
<ol>
<li><a href="#introduction-to-the-dom"><span class="secno">6.1 </span>Introduction to "The DOM"</a></li>
<li><a href="#node-tree"><span class="secno">6.2 </span>Node tree</a>
<ol>
<li><a href="#mutation-algorithms"><span class="secno">6.2.1 </span>Mutation algorithms</a></li>
<li><a href="#interface-parentnode"><span class="secno">6.2.2 </span>Interface <code>ParentNode</code></a></li>
<li><a href="#interface-childnode"><span class="secno">6.2.3 </span>Interface <code>ChildNode</code></a></li>
<li><a href="#collections:-elements"><span class="secno">6.2.4 </span>Collections: <code>Elements</code></a></li>
<li><a href="#old-style-collections:-nodelist-and-htmlcollection"><span class="secno">6.2.5 </span>Old-style collections: <code>NodeList</code> and <code>HTMLCollection</code></a>
<ol>
<li><a href="#interface-nodelist"><span class="secno">6.2.5.1 </span>Interface <code>NodeList</code></a></li>
<li><a href="#interface-htmlcollection"><span class="secno">6.2.5.2 </span>Interface <code>HTMLCollection</code></a></li></ol></li></ol></li>
<li><a href="#mutation-observers"><span class="secno">6.3 </span>Mutation observers</a>
<ol>
<li><a href="#interface-mutationobserver"><span class="secno">6.3.1 </span>Interface <code>MutationObserver</code></a></li>
<li><a href="#queuing-a-mutation-record"><span class="secno">6.3.2 </span>Queuing a mutation record</a></li>
<li><a href="#interface-mutationrecord"><span class="secno">6.3.3 </span>Interface <code>MutationRecord</code></a></li>
<li><a href="#garbage-collection"><span class="secno">6.3.4 </span>Garbage collection</a></li></ol></li>
<li><a href="#interface-node"><span class="secno">6.4 </span>Interface <code>Node</code></a></li>
<li><a href="#interface-document"><span class="secno">6.5 </span>Interface <code>Document</code></a>
<ol>
<li><a href="#interface-domimplementation"><span class="secno">6.5.1 </span>Interface <code>DOMImplementation</code></a></li></ol></li>
<li><a href="#interface-documentfragment"><span class="secno">6.6 </span>Interface <code>DocumentFragment</code></a></li>
<li><a href="#interface-documenttype"><span class="secno">6.7 </span>Interface <code>DocumentType</code></a></li>
<li><a href="#interface-element"><span class="secno">6.8 </span>Interface <code>Element</code></a>
<ol>
<li><a href="#interface-attr"><span class="secno">6.8.1 </span>Interface <code>Attr</code></a></li></ol></li>
<li><a href="#interface-characterdata"><span class="secno">6.9 </span>Interface <code>CharacterData</code></a></li>
<li><a href="#interface-text"><span class="secno">6.10 </span>Interface <code>Text</code></a></li>
<li><a href="#interface-processinginstruction"><span class="secno">6.11 </span>Interface <code>ProcessingInstruction</code></a></li>
<li><a href="#interface-comment"><span class="secno">6.12 </span>Interface <code>Comment</code></a></li></ol></li>
<li><a href="#ranges"><span class="secno">7 </span>Ranges</a>
<ol>
<li><a href="#introduction-to-dom-ranges"><span class="secno">7.1 </span>Introduction to "DOM Ranges"</a></li>
<li><a href="#interface-range"><span class="secno">7.2 </span>Interface <code>Range</code></a></li></ol></li>
<li><a href="#traversal"><span class="secno">8 </span>Traversal</a>
<ol>
<li><a href="#interface-nodeiterator"><span class="secno">8.1 </span>Interface <code>NodeIterator</code></a></li>
<li><a href="#interface-treewalker"><span class="secno">8.2 </span>Interface <code>TreeWalker</code></a></li>
<li><a href="#interface-nodefilter"><span class="secno">8.3 </span>Interface <code>NodeFilter</code></a></li></ol></li>
<li><a href="#sets"><span class="secno">9 </span>Sets</a>
<ol>
<li><a href="#interface-domtokenlist"><span class="secno">9.1 </span>Interface <code>DOMTokenList</code></a></li>
<li><a href="#interface-domsettabletokenlist"><span class="secno">9.2 </span>Interface <code>DOMSettableTokenList</code></a></li></ol></li>
<li><a href="#historical"><span class="secno">10 </span>Historical</a>
<ol>
<li><a href="#dom-events"><span class="secno">10.1 </span>DOM Events</a></li>
<li><a href="#dom-core"><span class="secno">10.2 </span>DOM Core</a></li>
<li><a href="#dom-ranges"><span class="secno">10.3 </span>DOM Ranges</a></li>
<li><a href="#dom-traversal"><span class="secno">10.4 </span>DOM Traversal</a></li></ol></li>
<li><a class="no-num" href="#references">References</a></li>
<li><a class="no-num" href="#acknowledgments">Acknowledgments</a></li></ol>
<!--end-toc-->
<h2 class="no-num" id="goals">Goals</h2>
</p><p>This specification standardizes the DOM. It does so as follows:</p>
<ol>
<li>
<p>By consolidating <cite>DOM Level 3 Core</cite>
<a class="informative" href="#refsDOM3CORE">[DOM3CORE]</a>,
<cite>Element Traversal</cite>
<a class="informative" href="#refsELEMENTTRAVERSAL">[ELEMENTTRAVERSAL]</a>,
<cite>Selectors API Level 2</cite>
<a class="informative" href="#refsSELECTORSAPI">[SELECTORSAPI]</a>, the
"DOM Event Architecture" and "Basic Event Interfaces" chapters of
<cite>DOM Level 3 Events</cite>
<a class="informative" href="#refsDOM3EVENTS">[DOM3EVENTS]</a> (specific type
of events do not belong in the base specification), and
<cite>DOM Level 2 Traversal and Range</cite>
<a class="informative" href="#refsDOM2TR">[DOM2TR]</a>, and:
<ul>
<li>Aligning them with the needs of JavaScript where possible.
</li><li>Aligning them with existing implementations.
</li><li>Simplifying them as much as possible.
</li></ul>
<li><p>By moving features from HTML5 that ought to be part of the DOM
platform here, while preventing a dependency on HTML5.
<a href="#refsHTML">[HTML]</a>
<li>
<p>By defining a replacement for the "Mutation Events" and
"Mutation Name Event Types" chapters of <cite>DOM Level 3 Events</cite>
<a class="informative" href="#refsDOM3EVENTS">[DOM3EVENTS]</a> as the old model
was problematic.
</p><p class="note">The old model is expected to be removed from implementations
in due course.
<li><p>By defining new features that simplify common DOM operations.
</p></li></p></li></p></li></p></li></ol>
<h2 id="conformance"><span class="secno">1 </span>Conformance</h2>
<p>All diagrams, examples, and notes in this specification are
non-normative, as are all sections explicitly marked non-normative.
Everything else in this specification is normative.
</p><p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC 2119.
For readability, these words do not appear in all uppercase letters in this
specification. <a href="#refsRFC2119">[RFC2119]</a>
</p><p>Requirements phrased in the imperative as part of algorithms
(such as "strip any leading space characters" or "return false and
terminate these steps") are to be interpreted with the meaning of the
key word ("must", "should", "may", etc) used in introducing the
algorithm.
</p><p>Conformance requirements phrased as algorithms or specific steps
may be implemented in any manner, so long as the end result is
equivalent. (In particular, the algorithms defined in this
specification are intended to be easy to follow, and not intended to
be performant.)
</p><p id="hardwareLimitations">User agents may impose
implementation-specific limits on otherwise unconstrained inputs,
e.g. to prevent denial of service attacks, to guard against running
out of memory, or to work around platform-specific limitations.
</p><p>When a method or an attribute is said to call another method or attribute, the user agent must invoke its internal API for that attribute or method so that e.g. the author can't change the behavior by overriding attributes or methods with custom properties or functions in JavaScript.
</p><p>Unless otherwise stated, string comparisons are done in a <a href="#case-sensitive">case-sensitive</a> manner.
<h3 id="dependencies"><span class="secno">1.1 </span>Dependencies</h3>
</p><p>The IDL fragments in this specification must be interpreted as
required for conforming IDL fragments, as described in the Web IDL
specification. <a href="#refsWEBIDL">[WEBIDL]</a>
</p><p>Some of the terms used in this specification are defined in
<cite>Encoding</cite>, <cite>Web IDL</cite>, <cite>XML</cite>, and
<cite>Namespaces in XML</cite>.
<a href="#refsENCODING">[ENCODING]</a>
<a href="#refsWEBIDL">[WEBIDL]</a>
<a href="#refsXML">[XML]</a>
<a href="#refsXMLNS">[XMLNS]</a>
<h3 id="extensibility"><span class="secno">1.2 </span>Extensibility</h3>
</p><p>Vendor-specific proprietary extensions to this specification are
strongly discouraged. Authors must not use such extensions, as
doing so reduces interoperability and fragments the user base,
allowing only users of specific user agents to access the content in
question.
</p><p>If vendor-specific extensions are needed, the members should be
prefixed by vendor-specific strings to prevent clashes with future
versions of this specification. Extensions must be defined so that
the use of extensions neither contradicts nor causes the
non-conformance of functionality defined in the specification.
<!-- thanks to QA Framework -->
</p><p>When vendor-neutral extensions to this specification are needed,
either this specification can be updated accordingly, or an
extension specification can be written that overrides the
requirements in this specification. When someone applying this
specification to their activities decides that they will recognize
the requirements of such an extension specification, it becomes an
<dfn id="other-applicable-specifications" title="other applicable specifications">applicable
specification</dfn> for the purposes of conformance requirements in
this specification.
<!-- http://www.w3.org/mid/[email protected] -->
<h2 id="terminology"><span class="secno">2 </span>Terminology</h2>
</p><p>The term <dfn id="context-object">context object</dfn> means the object on which the algorithm,
attribute getter, attribute setter, or method being discussed was called. When the
<a href="#context-object">context object</a> is unambiguous, the term can be omitted.
<!-- XXX we should prolly explain that "set attribute X to Y" works even for
readonly attributes when it is language for implementors -->
<h3 id="trees"><span class="secno">2.1 </span>Trees</h3> <!-- Sorry reddit, this is not /r/trees -->
</p><p>A <dfn id="concept-tree" title="concept-tree">tree</dfn> is a finite hierarchical tree structure. In
<dfn id="concept-tree-order" title="concept-tree-order">tree order</dfn> is preorder, depth-first
traversal of a <a href="#concept-tree" title="concept-tree">tree</a>.
<!-- http://en.wikipedia.org/wiki/Tree_traversal#Depth-first_Traversal -->
</p><p>An object that <dfn id="concept-tree-participate" title="concept-tree-participate">participates</dfn> in
a <a href="#concept-tree" title="concept-tree">tree</a> has a
<dfn id="concept-tree-parent" title="concept-tree-parent">parent</dfn>, which is either another object
or null, and an ordered list of zero or more
<dfn id="concept-tree-child" title="concept-tree-child">child</dfn> objects. An object <var title="">A</var> whose
<a href="#concept-tree-parent" title="concept-tree-parent">parent</a> is object <var title="">B</var> is a
<a href="#concept-tree-child" title="concept-tree-child">child</a> of <var title="">B</var>.
</p><p>The <dfn id="concept-tree-root" title="concept-tree-root">root</dfn> of an object is itself, if its
<a href="#concept-tree-parent" title="concept-tree-parent">parent</a> is null, or else it is the
<a href="#concept-tree-root" title="concept-tree-root">root</a> of its
<a href="#concept-tree-parent" title="concept-tree-parent">parent</a>.
</p><p>An object <var title="">A</var> is called a
<dfn id="concept-tree-descendant" title="concept-tree-descendant">descendant</dfn> of an object
<var title="">B</var>, if either <var title="">A</var> is a
<a href="#concept-tree-child" title="concept-tree-child">child</a> of <var title="">B</var> or
<var title="">A</var> is a <a href="#concept-tree-child" title="concept-tree-child">child</a> of an
object <var title="">C</var> that is a
<a href="#concept-tree-descendant" title="concept-tree-descendant">descendant</a> of <var title="">B</var>.
</p><p>An
<dfn id="concept-tree-inclusive-descendant" title="concept-tree-inclusive-descendant">inclusive descendant</dfn> is
an object or one of its
<a href="#concept-tree-descendant" title="concept-tree-descendant">descendants</a>.
</p><p>An object <var title="">A</var> is called an
<dfn id="concept-tree-ancestor" title="concept-tree-ancestor">ancestor</dfn> of an object
<var title="">B</var> if and only if <var title="">B</var> is a
<a href="#concept-tree-descendant" title="concept-tree-descendant">descendant</a> of
<var title="">A</var>.
</p><p>An <dfn id="concept-tree-inclusive-ancestor" title="concept-tree-inclusive-ancestor">inclusive ancestor</dfn> is
an object or one of its <a href="#concept-tree-ancestor" title="concept-tree-ancestor">ancestors</a>.
</p><p>An object <var title="">A</var> is called a
<dfn id="concept-tree-sibling" title="concept-tree-sibling">sibling</dfn> of an object
<var title="">B</var>, if and only if <var title="">B</var> and <var title="">A</var>
share the same non-null <a href="#concept-tree-parent" title="concept-tree-parent">parent</a>.
</p><p>An object <var title="">A</var> is
<dfn id="concept-tree-preceding" title="concept-tree-preceding">preceding</dfn> an object
<var title="">B</var> if <var title="">A</var> and <var title="">B</var> are in the
same <a href="#concept-tree" title="concept-tree">tree</a> and <var title="">A</var> comes
before <var title="">B</var> in
<a href="#concept-tree-order" title="concept-tree-order">tree order</a>.
</p><p>An object <var title="">A</var> is
<dfn id="concept-tree-following" title="concept-tree-following">following</dfn> an object
<var title="">B</var> if <var title="">A</var> and <var title="">B</var> are in the
same <a href="#concept-tree" title="concept-tree">tree</a> and <var title="">A</var> comes
after <var title="">B</var> in
<a href="#concept-tree-order" title="concept-tree-order">tree order</a>.
</p><p>The <dfn id="concept-tree-first-child" title="concept-tree-first-child">first child</dfn> of an object is
its first <a href="#concept-tree-child" title="concept-tree-child">child</a> or null if it has no
<a href="#concept-tree-child" title="concept-tree-child">child</a>.
</p><p>The <dfn id="concept-tree-last-child" title="concept-tree-last-child">last child</dfn> of an object is
its last <a href="#concept-tree-child" title="concept-tree-child">child</a> or null if it has no
<a href="#concept-tree-child" title="concept-tree-child">child</a>.
</p><p>The <dfn id="concept-tree-previous-sibling" title="concept-tree-previous-sibling">previous sibling</dfn> of an
object is its first <a href="#concept-tree-preceding" title="concept-tree-preceding">preceding</a>
<a href="#concept-tree-sibling" title="concept-tree-sibling">sibling</a> or null if it has no
<a href="#concept-tree-preceding" title="concept-tree-preceding">preceding</a>
<a href="#concept-tree-sibling" title="concept-tree-sibling">sibling</a>.
</p><p>The <dfn id="concept-tree-next-sibling" title="concept-tree-next-sibling">next sibling</dfn> of an
object is its first <a href="#concept-tree-following" title="concept-tree-following">following</a>
<a href="#concept-tree-sibling" title="concept-tree-sibling">sibling</a> or null if it has no
<a href="#concept-tree-following" title="concept-tree-following">following</a>
<a href="#concept-tree-sibling" title="concept-tree-sibling">sibling</a>.
</p><p>The <dfn id="concept-tree-index" title="concept-tree-index">index</dfn> of an object is its number
of <a href="#concept-tree-preceding" title="concept-tree-preceding">preceding</a>
<a href="#concept-tree-sibling" title="concept-tree-sibling">siblings</a>.
<h3 id="strings"><span class="secno">2.2 </span>Strings</h3>
</p><p>Comparing two strings in a <dfn id="case-sensitive">case-sensitive</dfn> manner means comparing them exactly, code point for code point.
</p><p>Comparing two strings in a <dfn id="ascii-case-insensitive">ASCII case-insensitive</dfn> manner means comparing them exactly, code point for code point, except that the characters in the range U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) and the corresponding characters in the range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z) are considered to also match.
</p><p><dfn id="converted-to-ascii-uppercase" title="converted to ascii uppercase">Converting a string to ASCII uppercase</dfn> means replacing all characters in the range U+0061 to U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z) with the corresponding characters in the range U+0041 to U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).
</p><p><dfn id="converted-to-ascii-lowercase" title="converted to ascii lowercase">Converting a string to ASCII lowercase</dfn> means replacing all characters in the range U+0041 to U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) with the corresponding characters in the range U+0061 to U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z).
</p><p>A string <var title="">pattern</var> is a <dfn id="prefix-match">prefix match</dfn> for a string
<var title="">s</var> when <var title="">pattern</var> is not longer than
<var title="">s</var> and truncating <var title="">s</var> to
<var title="">pattern</var>'s length leaves the two strings as matches of each
other.
<h3 id="ordered-sets"><span class="secno">2.3 </span>Ordered sets</h3>
</p><p>The <dfn id="concept-ordered-set-parser" title="concept-ordered-set-parser">ordered set parser</dfn> takes a string
<var title="">input</var> and then runs these steps:
<ol>
<li><p>Let <var title="">position</var> be a pointer into <var title="">input</var>,
initially pointing at the start of the string.
<li><p>Let <var title="">tokens</var> be an ordered set of tokens, initially empty.
<li><p><a href="#skip-ascii-whitespace">Skip ASCII whitespace</a>.
<li><p>While <var title="">position</var> is not past the end of
<var title="">input</var>:
<ol>
<li><p><a href="#collect-a-code-point-sequence">Collect a code point sequence</a> of code points that are
not <a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#ascii-whitespace">ASCII whitespace</a>.
<li><p>If the collected string is not in <var title="">tokens</var>, append the
collected string to <var title="">tokens</var>.
<li><p><a href="#skip-ascii-whitespace">Skip ASCII whitespace</a>.
</p></li></p></li></p></li></ol>
<li><p>Return <var title="">tokens</var>.
</p></li></p></li></p></li></p></li></p></li></ol>
</p><p>To <dfn id="collect-a-code-point-sequence">collect a code point sequence</dfn> of
<var title="">code points</var>, run these steps:
<ol>
<li><p>Let <var title="">input</var> and <var title="">position</var> be the same
variables as those of the same name in the algorithm that invoked these
steps.
<li><p>Let <var title="">result</var> be the empty string.
<li><p>While <var title="">position</var> does not point past the end of
<var title="">input</var> and the code point at <var title="">position</var> is
one of <var title="">code points</var>, append that code point to the end
of <var title="">result</var> and advance <var title="">position</var> to the
next code point in <var title="">input</var>.
<li><p>Return <var title="">result</var>.
</p></li></p></li></p></li></p></li></ol>
</p><p>To <dfn id="skip-ascii-whitespace">skip ASCII whitespace</dfn> means to
<a href="#collect-a-code-point-sequence">collect a code point sequence</a> of
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#ascii-whitespace">ASCII whitespace</a> and discard the
return value.
</p><p>The <dfn id="concept-ordered-set-serializer" title="concept-ordered-set-serializer">ordered set serializer</dfn> takes a
<var title="">set</var> and returns the concatenation of the strings in
<var title="">set</var>, separated from each other by U+0020.
<h3 id="namespaces"><span class="secno">2.4 </span>Namespaces</h3>
</p><p>The <dfn id="html-namespace">HTML namespace</dfn> is
<code title="">http://www.w3.org/1999/xhtml</code>.
</p><p>The <dfn id="xml-namespace">XML namespace</dfn> is
<code title="">http://www.w3.org/XML/1998/namespace</code>.
</p><p>The <dfn id="xmlns-namespace">XMLNS namespace</dfn> is
<code title="">http://www.w3.org/2000/xmlns/</code>.
<h2 id="errors"><span class="secno">3 </span>Errors</h2>
<h3 id="exception-domexception"><span class="secno">3.1 </span>Exception <code><a href="#domexception">DOMException</a></code></h3>
<pre class="idl">exception <dfn id="domexception">DOMException</dfn> {
const unsigned short <a href="#dom-domexception-index_size_err" title="dom-DOMException-INDEX_SIZE_ERR">INDEX_SIZE_ERR</a> = 1;
const unsigned short <span title="dom-DOMException-DOMSTRING_SIZE_ERR">DOMSTRING_SIZE_ERR</span> = 2; // historical
const unsigned short <a href="#dom-domexception-hierarchy_request_err" title="dom-DOMException-HIERARCHY_REQUEST_ERR">HIERARCHY_REQUEST_ERR</a> = 3;
const unsigned short <a href="#dom-domexception-wrong_document_err" title="dom-DOMException-WRONG_DOCUMENT_ERR">WRONG_DOCUMENT_ERR</a> = 4;
const unsigned short <a href="#dom-domexception-invalid_character_err" title="dom-DOMException-INVALID_CHARACTER_ERR">INVALID_CHARACTER_ERR</a> = 5;
const unsigned short <span title="dom-DOMException-NO_DATA_ALLOWED_ERR">NO_DATA_ALLOWED_ERR</span> = 6; // historical
const unsigned short <a href="#dom-domexception-no_modification_allowed_err" title="dom-DOMException-NO_MODIFICATION_ALLOWED_ERR">NO_MODIFICATION_ALLOWED_ERR</a> = 7;
const unsigned short <a href="#dom-domexception-not_found_err" title="dom-DOMException-NOT_FOUND_ERR">NOT_FOUND_ERR</a> = 8;
const unsigned short <a href="#dom-domexception-not_supported_err" title="dom-DOMException-NOT_SUPPORTED_ERR">NOT_SUPPORTED_ERR</a> = 9;
const unsigned short <span title="dom-DOMException-INUSE_ATTRIBUTE_ERR">INUSE_ATTRIBUTE_ERR</span> = 10; // historical
const unsigned short <a href="#dom-domexception-invalid_state_err" title="dom-DOMException-INVALID_STATE_ERR">INVALID_STATE_ERR</a> = 11;
const unsigned short <a href="#dom-domexception-syntax_err" title="dom-DOMException-SYNTAX_ERR">SYNTAX_ERR</a> = 12;
const unsigned short <a href="#dom-domexception-invalid_modification_err" title="dom-DOMException-INVALID_MODIFICATION_ERR">INVALID_MODIFICATION_ERR</a> = 13;
const unsigned short <a href="#dom-domexception-namespace_err" title="dom-DOMException-NAMESPACE_ERR">NAMESPACE_ERR</a> = 14;
const unsigned short <a href="#dom-domexception-invalid_access_err" title="dom-DOMException-INVALID_ACCESS_ERR">INVALID_ACCESS_ERR</a> = 15;
const unsigned short <span title="dom-DOMException-VALIDATION_ERR">VALIDATION_ERR</span> = 16; // historical
const unsigned short <span title="dom-DOMException-TYPE_MISMATCH_ERR">TYPE_MISMATCH_ERR</span> = 17; // historical; use JavaScript's TypeError instead
const unsigned short <a href="#dom-domexception-security_err" title="dom-DOMException-SECURITY_ERR">SECURITY_ERR</a> = 18;
const unsigned short <a href="#dom-domexception-network_err" title="dom-DOMException-NETWORK_ERR">NETWORK_ERR</a> = 19;
const unsigned short <a href="#dom-domexception-abort_err" title="dom-DOMException-ABORT_ERR">ABORT_ERR</a> = 20;
const unsigned short <a href="#dom-domexception-url_mismatch_err" title="dom-DOMException-URL_MISMATCH_ERR">URL_MISMATCH_ERR</a> = 21;
const unsigned short <a href="#dom-domexception-quota_exceeded_err" title="dom-DOMException-QUOTA_EXCEEDED_ERR">QUOTA_EXCEEDED_ERR</a> = 22;
const unsigned short <a href="#dom-domexception-timeout_err" title="dom-DOMException-TIMEOUT_ERR">TIMEOUT_ERR</a> = 23;
const unsigned short <a href="#dom-domexception-invalid_node_type_err" title="dom-DOMException-INVALID_NODE_TYPE_ERR">INVALID_NODE_TYPE_ERR</a> = 24;
const unsigned short <a href="#dom-domexception-data_clone_err" title="dom-DOMException-DATA_CLONE_ERR">DATA_CLONE_ERR</a> = 25;
unsigned short <a href="#dom-domexception-code" title="dom-DOMException-code">code</a>;
};</pre>
</p><p>The <dfn id="dom-domexception-code" title="dom-DOMException-code"><code>code</code></dfn> exception
field must return the value it was initialized to.
</p><p>To <dfn id="concept-throw" title="concept-throw">throw</dfn> a <var title="">name</var> exception
run these steps:
<ol>
<li><p>Let <var title="">code</var> be zero.
<li><p>If <var title="">name</var> is in the first column of the
<a href="#error-names-table">error names table</a> and has a corresponding legacy
<code title="dom-DOMException-code"><a href="#dom-domexception-code">code</a></code> exception field value in the
third column, set <var title="">code</var> to that value.
<li><p><a class="external" data-anolis-spec="webidl" href="http://dev.w3.org/2006/webapi/WebIDL/#dfn-throw">Throw</a> a new
<code><a href="#domexception">DOMException</a></code> exception, whose
<a class="external" data-anolis-spec="webidl" href="http://dev.w3.org/2006/webapi/WebIDL/#dfn-exception-message">message</a> is a user agent-defined value,
<a class="external" data-anolis-spec="webidl" href="http://dev.w3.org/2006/webapi/WebIDL/#dfn-exception-name">name</a> is <var title="">name</var>, and
whose <code title="dom-DOMException-code"><a href="#dom-domexception-code">code</a></code> exception field is
<var title="">code</var>.
</p></li></p></li></p></li></ol>
</p><p class="example">To
<i title="">throw a "<code><a href="#timeouterror">TimeoutError</a></code>" exception</i>, a
user agent would construct a <code><a href="#domexception">DOMException</a></code> exception whose
<a class="external" data-anolis-spec="webidl" href="http://dev.w3.org/2006/webapi/WebIDL/#dfn-exception-name">name</a> is
"<code><a href="#timeouterror">TimeoutError</a></code>" and
<code title="dom-DOMException-code"><a href="#dom-domexception-code">code</a></code> exception field value is 23,
and actually throw that object as an exception. In JavaScript, this
exception will have a <code title="">name</code> property whose value is
"<code><a href="#timeouterror">TimeoutError</a></code>".
<h3 id="interface-domerror"><span class="secno">3.2 </span>Interface <code><a href="#domerror">DOMError</a></code></h3>
<pre class="idl">[<a href="#dom-domerror" title="dom-DOMError">Constructor</a>(DOMString <var title="">name</var>, optional DOMString <var title="">message</var> = "")]
interface <dfn id="domerror">DOMError</dfn> {
readonly attribute DOMString <a href="#dom-domerror-name" title="dom-DOMError-name">name</a>;
readonly attribute DOMString <a href="#dom-domerror-message" title="dom-DOMError-message">message</a>;
};</pre>
</p><p class="XXX"><code><a href="#domerror">DOMError</a></code> might be nuked in favor of using
<code><a href="#domexception">DOMException</a></code> exclusively. See <a href="https://mail.mozilla.org/pipermail/es-discuss/2013-July/thread.html#31677">Creating your own errors</a>
on es-discuss for more details.
</p><p class="note">This interface is intended for other specifications that want
to introduce error handling through other means than exceptions. As with
exceptions, the <a href="#error-names-table">error names table</a> is used.
</p><p>The <dfn id="dom-domerror" title="dom-DOMError"><code>DOMError(<var title="">name</var>, <var title="">message</var>)</code></dfn>
constructor must return a new <code><a href="#domerror">DOMError</a></code> object whose
<code title="dom-DOMError-name"><a href="#dom-domerror-name">name</a></code> attribute is initialized to
<var title="">name</var> and whose <code title="dom-DOMError-message"><a href="#dom-domerror-message">message</a></code> attribute
is initialized to <var title="">message</var>.
</p><p>The <dfn id="dom-domerror-name" title="dom-DOMError-name"><code>name</code></dfn> attribute must
return the value it was initialized to.
</p><p>The <dfn id="dom-domerror-message" title="dom-DOMError-message"><code>message</code></dfn> attribute must
return the value it was initialized to.
</p><p class="note">The value of the <code title="dom-DOMError-message"><a href="#dom-domerror-message">message</a></code> will
typically be implementation-dependent and for informational purposes only.
</p><p>A
<dfn id="concept-domerror" title="concept-DOMError"><var title="">name</var> <code>DOMError</code></dfn>
means a <code><a href="#domerror">DOMError</a></code> object whose
<code title="dom-DOMError-name"><a href="#dom-domerror-name">name</a></code> attribute is initialized to
<var title="">name</var> and whose <code title="dom-DOMError-message"><a href="#dom-domerror-message">message</a></code> attribute
is initialized to a helpful implementation-dependent message that explains the error.
</p><p class="example">A specification could say that an <code title="">error</code>
attribute must return a
<a href="#concept-domerror" title="concept-DOMError">"<code>SyntaxError</code>" <code>DOMError</code></a>.
<h3 id="error-names-0"><span class="secno">3.3 </span>Error names</h3>
</p><p>The <dfn id="error-names-table">error names table</dfn> below lists all the allowed error names,
a description, and legacy <code title="dom-DOMException-code"><a href="#dom-domexception-code">code</a></code>
exception field values (when the error name is used for
<a href="#concept-throw" title="concept-throw">throwing</a> an exception).
</p><p class="note">If an error name is not listed here, please file a bug as
indicated at the top of this specification and it will be addressed shortly.
Thanks!
<table id="error-names">
<thead>
<tr><th>Name</th><th>Description</th><th>Legacy <code title="dom-DOMException-code"><a href="#dom-domexception-code">code</a></code> exception field value (if any)
<tbody>
<tr>
<td>"<dfn id="indexsizeerror"><code>IndexSizeError</code></dfn>"
</td><td>The index is not in the allowed range.
</td><td><dfn id="dom-domexception-index_size_err" title="dom-DOMException-INDEX_SIZE_ERR"><code>INDEX_SIZE_ERR</code></dfn> (1)
</td></tr><tr>
<td>"<dfn id="hierarchyrequesterror"><code>HierarchyRequestError</code></dfn>"
</td><td>The operation would yield an incorrect <a href="#concept-node-tree" title="concept-node-tree">node tree</a>.
</td><td><dfn id="dom-domexception-hierarchy_request_err" title="dom-DOMException-HIERARCHY_REQUEST_ERR"><code>HIERARCHY_REQUEST_ERR</code></dfn> (3)
</td></tr><tr>
<td>"<dfn id="wrongdocumenterror"><code>WrongDocumentError</code></dfn>"
</td><td>The object is in the wrong <a href="#concept-document" title="concept-document">document</a>.
</td><td><dfn id="dom-domexception-wrong_document_err" title="dom-DOMException-WRONG_DOCUMENT_ERR"><code>WRONG_DOCUMENT_ERR</code></dfn> (4)
</td></tr><tr>
<td>"<dfn id="invalidcharactererror"><code>InvalidCharacterError</code></dfn>"
</td><td>The string contains invalid characters.
</td><td><dfn id="dom-domexception-invalid_character_err" title="dom-DOMException-INVALID_CHARACTER_ERR"><code>INVALID_CHARACTER_ERR</code></dfn> (5)
</td></tr><tr>
<td>"<dfn id="nomodificationallowederror"><code>NoModificationAllowedError</code></dfn>"
</td><td>The object can not be modified.
</td><td><dfn id="dom-domexception-no_modification_allowed_err" title="dom-DOMException-NO_MODIFICATION_ALLOWED_ERR"><code>NO_MODIFICATION_ALLOWED_ERR</code></dfn> (7)
</td></tr><tr>
<td>"<dfn id="notfounderror"><code>NotFoundError</code></dfn>"
</td><td>The object can not be found here.
</td><td><dfn id="dom-domexception-not_found_err" title="dom-DOMException-NOT_FOUND_ERR"><code>NOT_FOUND_ERR</code></dfn> (8)
</td></tr><tr>
<td>"<dfn id="notsupportederror"><code>NotSupportedError</code></dfn>"
</td><td>The operation is not supported.
</td><td><dfn id="dom-domexception-not_supported_err" title="dom-DOMException-NOT_SUPPORTED_ERR"><code>NOT_SUPPORTED_ERR</code></dfn> (9)
</td></tr><tr>
<td>"<dfn id="invalidstateerror"><code>InvalidStateError</code></dfn>"
</td><td>The object is in an invalid state.
</td><td><dfn id="dom-domexception-invalid_state_err" title="dom-DOMException-INVALID_STATE_ERR"><code>INVALID_STATE_ERR</code></dfn> (11)
</td></tr><tr>
<td>"<dfn id="syntaxerror"><code>SyntaxError</code></dfn>"
</td><td>The string did not match the expected pattern.
</td><td><dfn id="dom-domexception-syntax_err" title="dom-DOMException-SYNTAX_ERR"><code>SYNTAX_ERR</code></dfn> (12)
</td></tr><tr>
<td>"<dfn id="invalidmodificationerror"><code>InvalidModificationError</code></dfn>"
</td><td>The object can not be modified in this way.
</td><td><dfn id="dom-domexception-invalid_modification_err" title="dom-DOMException-INVALID_MODIFICATION_ERR"><code>INVALID_MODIFICATION_ERR</code></dfn> (13)
</td></tr><tr>
<td>"<dfn id="namespaceerror"><code>NamespaceError</code></dfn>"
</td><td>The operation is not allowed by <cite>Namespaces in XML</cite>. <a href="#refsXMLNS">[XMLNS]</a>
</td><td><dfn id="dom-domexception-namespace_err" title="dom-DOMException-NAMESPACE_ERR"><code>NAMESPACE_ERR</code></dfn> (14)
</td></tr><tr>
<td>"<dfn id="invalidaccesserror"><code>InvalidAccessError</code></dfn>"
</td><td>The object does not support the operation or argument.
</td><td><dfn id="dom-domexception-invalid_access_err" title="dom-DOMException-INVALID_ACCESS_ERR"><code>INVALID_ACCESS_ERR</code></dfn> (15)
</td></tr><tr>
<!-- XHR -->
<td>"<dfn id="securityerror"><code>SecurityError</code></dfn>"
</td><td>The operation is insecure.
</td><td><dfn id="dom-domexception-security_err" title="dom-DOMException-SECURITY_ERR"><code>SECURITY_ERR</code></dfn> (18)
</td></tr><tr>
<!-- XHR -->
<td>"<dfn id="networkerror"><code>NetworkError</code></dfn>"
</td><td>A network error occurred.
</td><td><dfn id="dom-domexception-network_err" title="dom-DOMException-NETWORK_ERR"><code>NETWORK_ERR</code></dfn> (19)
</td></tr><tr>
<!-- XHR -->
<td>"<dfn id="aborterror"><code>AbortError</code></dfn>"
</td><td>The operation was aborted.
</td><td><dfn id="dom-domexception-abort_err" title="dom-DOMException-ABORT_ERR"><code>ABORT_ERR</code></dfn> (20)
</td></tr><tr>
<!-- Workers -->
<td>"<dfn id="urlmismatcherror"><code>URLMismatchError</code></dfn>"
</td><td>The given URL does not match another URL.
</td><td><dfn id="dom-domexception-url_mismatch_err" title="dom-DOMException-URL_MISMATCH_ERR"><code>URL_MISMATCH_ERR</code></dfn> (21)
</td></tr><tr>
<!-- HTML -->
<td>"<dfn id="quotaexceedederror"><code>QuotaExceededError</code></dfn>"
</td><td>The quota has been exceeded.
</td><td><dfn id="dom-domexception-quota_exceeded_err" title="dom-DOMException-QUOTA_EXCEEDED_ERR"><code>QUOTA_EXCEEDED_ERR</code></dfn> (22)
</td></tr><tr>
<!-- XHR -->
<td>"<dfn id="timeouterror"><code>TimeoutError</code></dfn>"
</td><td>The operation timed out.
</td><td><dfn id="dom-domexception-timeout_err" title="dom-DOMException-TIMEOUT_ERR"><code>TIMEOUT_ERR</code></dfn> (23)
</td></tr><tr>
<td>"<dfn id="invalidnodetypeerror"><code>InvalidNodeTypeError</code></dfn>"
</td><td>The supplied node is incorrect or has an incorrect ancestor for this operation.
</td><td><dfn id="dom-domexception-invalid_node_type_err" title="dom-DOMException-INVALID_NODE_TYPE_ERR"><code>INVALID_NODE_TYPE_ERR</code></dfn> (24)
</td></tr><tr>
<!-- HTML -->
<td>"<dfn id="datacloneerror"><code>DataCloneError</code></dfn>"
</td><td>The object can not be cloned.
</td><td><dfn id="dom-domexception-data_clone_err" title="dom-DOMException-DATA_CLONE_ERR"><code>DATA_CLONE_ERR</code></dfn> (25)
</td></tr><tr>
<td>"<dfn id="encodingerror"><code>EncodingError</code></dfn>"
</td><td>The encoding operation (either encoded or decoding) failed.
</td><td>—
</td></tr></tbody></th></tr></thead></table>
<h2 id="promises"><span class="secno">4 </span>Promises</h2>
</p><p class="note" id="futures">This feature used to be called futures.
<h3 id="i-promise-you-an-introduction"><span class="secno">4.1 </span>I <code title="">Promise</code> you an introduction</h3>
</p><p><span title="concept-promise">Promises</span> provide a convenient way to get access to the
result of an operation.
</p><p><span title="concept-promise">Promises</span> can be returned by platform APIs, but can
also be used in conjunction with an existing API to make it easier to work with.
<div class="example">
<p>This example demonstrates creating a <code title="">fetchJSON(<var>url</var>)</code>
function that returns a <code>Promise</code> that is responsible for fetching a
<a class="external" data-anolis-spec="url" href="http://url.spec.whatwg.org/#url">URL</a> and parsing the response as JSON.
<pre>function fetchJSON(url) {
return new Promise(function(resolve, reject) {
var xhr = new XMLHttpRequest()
xhr.open("GET", url)
xhr.responseType = "json"
xhr.send()
// reject() is ignored once resolve() has been invoked
xhr.onload = function() {
if(xhr.response)
resolve(xhr.response)
reject(new TypeError)
}
xhr.onloadend = function() { reject(new TypeError) }
})
}</pre>
</p><p>This can be used to create more idiomatic code:
<pre>fetchJSON("/user/posts").then(showPosts, showFailcat)</pre>
</p><p>Using static methods <span title="concept-promise">promises</span> can be combined to
create new <span title="concept-promise">promises</span>, which allows for operating on the
results of several asynchronous requests at once:
<pre>Promise.all([fetchJSON("/user/mario"), fetchJSON("/user/luigi")]).then(
function([mario, luigi]) { … },
showFailcat
)</pre>
</p><p>Enjoy!
</p></div>
<h3 id="open-issues"><span class="secno">4.2 </span>Open issues</h3>
</p><p class="XXX">The task model for promises will change:
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=22296">microtask and promises</a>.
</p><p class="XXX">Promises is temporarily drafted elsewhere: <a href="https://github.com/domenic/promises-unwrapping/blob/master/README.md">Promises Objects</a>.
<h2 id="events"><span class="secno">5 </span>Events</h2>
<h3 id="introduction-to-dom-events"><span class="secno">5.1 </span>Introduction to "DOM Events"</h3>
</p><p>Throughout the web platform <a href="#concept-event" title="concept-event">events</a> are
<a href="#concept-event-dispatch" title="concept-event-dispatch">dispatched</a> to objects to signal an
occurrence, such as network activity or user interaction. These objects
implement the <code><a href="#eventtarget">EventTarget</a></code> interface and can therefore add
<a href="#concept-event-listener" title="concept-event-listener">event listeners</a> to observe
<a href="#concept-event" title="concept-event">events</a>:
<pre><code>obj.addEventListener("load", imgFetched)
function imgFetched(ev) {
// great success
…
}</code></pre>
</p><p><a href="#concept-event-listener" title="concept-event-listener">Event listeners</a> can be removed
by utilizing the
<code title="dom-EventTarget-removeEventListener"><a href="#dom-eventtarget-removeeventlistener">removeEventListener()</a></code>
method, passing the same arguments.
</p><p><a href="#concept-event" title="concept-event">Events</a> are objects too and implement the
<code><a href="#event">Event</a></code> interface (or a derived interface). In the example above
<var title="">ev</var> is the <a href="#concept-event" title="concept-event">event</a>. It is
passed as argument to
<a href="#concept-event-listener" title="concept-event-listener">event listener</a>'s <b>callback</b>
(typically a JavaScript Function as shown above).
<a href="#concept-event-listener" title="concept-event-listener">Event listeners</a> key off the
<a href="#concept-event" title="concept-event">event</a>'s
<code title="dom-Event-type"><a href="#dom-event-type">type</a></code> attribute value
("<code title="">load</code>" in the above example). The
<a href="#concept-event" title="concept-event">event</a>'s
<code title="dom-Event-target"><a href="#dom-event-target">target</a></code> attribute value returns the
object to which the <a href="#concept-event" title="concept-event">event</a> was
<a href="#concept-event-dispatch" title="concept-event-dispatch">dispatched</a> (<var title="">obj</var>
above).
</p><p>Now while typically <a href="#concept-event" title="concept-event">events</a> are
<a href="#concept-event-dispatch" title="concept-event-dispatch">dispatched</a> by the user agent as
the result of user interaction or the completion of some task, applications
can <a href="#concept-event-dispatch" title="concept-event-dispatch">dispatch</a>
<a href="#concept-event" title="concept-event">events</a> themselves, commonly known as
synthetic events:
<pre><code>// add an appropriate event listener
obj.addEventListener("cat", function(e) { process(e.detail) })
// create and dispatch the event
var event = new CustomEvent("cat", {"detail":{"hazcheeseburger":true}})
obj.dispatchEvent(event)</code></pre>
</p><p>Apart from signaling, <a href="#concept-event" title="concept-event">events</a> are
sometimes also used to let an application control what happens next in an
operation. For instance as part of form submission an
<a href="#concept-event" title="concept-event">event</a> whose
<code title="dom-Event-type"><a href="#dom-event-type">type</a></code> attribute value is
"<code title="">submit</code>" is
<a href="#concept-event-dispatch" title="concept-event-dispatch">dispatched</a>. If this
<a href="#concept-event" title="concept-event">event</a>'s
<code title="dom-Event-preventDefault"><a href="#dom-event-preventdefault">preventDefault()</a></code> method is
invoked, form submission will be terminated. Applications who wish to make
use of this functionality through <a href="#concept-event" title="concept-event">events</a>
<a href="#concept-event-dispatch" title="concept-event-dispatch">dispatched</a> by the application
(synthetic events) can make use of the return value of the
<code title="dom-EventTarget-dispatchEvent"><a href="#dom-eventtarget-dispatchevent">dispatchEvent()</a></code> method:
<pre><code>if(obj.dispatchEvent(event)) {
// event was not canceled, time for some magic
…
}</code></pre>
</p><p>When an <a href="#concept-event" title="concept-event">event</a> is
<a href="#concept-event-dispatch" title="concept-event-dispatch">dispatched</a> to an object that
<a href="#concept-tree-participate" title="concept-tree-participate">participates</a> in a
<a href="#concept-tree" title="concept-tree">tree</a> (e.g. an
<a href="#concept-element" title="concept-element">element</a>), it can reach
<a href="#concept-event-listener" title="concept-event-listener">event listeners</a> on that object's
<a href="#concept-tree-ancestor" title="concept-tree-ancestor">ancestors</a> too. First all object's
<a href="#concept-tree-ancestor" title="concept-tree-ancestor">ancestor</a>
<a href="#concept-event-listener" title="concept-event-listener">event listeners</a> whose
<b>capture</b> variable is set to true are invoked, in
<a href="#concept-tree-order" title="concept-tree-order">tree order</a>. Second, object's own
<a href="#concept-event-listener" title="concept-event-listener">event listeners</a> are invoked. And
finally, and only if <a href="#concept-event" title="concept-event">event</a>'s
<a href="#dom-event-bubbles" title="dom-Event-bubbles">bubbles</a> attribute value is true,
object's <a href="#concept-tree-ancestor" title="concept-tree-ancestor">ancestor</a>
<a href="#concept-event-listener" title="concept-event-listener">event listeners</a> are invoked again,
but now in reverse <a href="#concept-tree-order" title="concept-tree-order">tree order</a>.
</p><p>Lets look at an example on how <a href="#concept-event" title="concept-event">events</a>
work in a <a href="#concept-tree" title="concept-tree">tree</a>:
<pre><code><!doctype html>
<html>
<head>
<title>Boring example</title>
</head>
<body>
<p>Hello <span id=x>world</span>!</p>
<script>
function test(e) {
debug(e.target, e.currentTarget, e.eventPhase)
}
document.addEventListener("hey", test, true)
document.body.addEventListener("hey", test)
var ev = new Event("hey", {bubbles:true})
document.getElementById("x").dispatchEvent(ev)
</script>
</body>
</html></code></pre>
</p><p>The <code title="">debug</code> function will be invoked twice. Each time
the <a href="#concept-event" title="concept-event">events</a>'s
<code title="dom-Event-target"><a href="#dom-event-target">target</a></code> attribute value will be the
<code title="">span</code> <a href="#concept-element" title="concept-element">element</a>. The
first time <code title="dom-Event-target"><a href="#dom-event-target">currentTarget</a></code> attribute's
value will be the <a href="#concept-document" title="concept-document">document</a>, the second
time the <code title="">body</code> <a href="#concept-element" title="concept-element">element</a>.
<code title="dom-Event-eventPhase"><a href="#dom-event-eventphase">eventPhase</a></code> attribute's value
switches from <code title="dom-Event-CAPTURING_PHASE"><a href="#dom-event-capturing_phase">CAPTURING_PHASE</a></code>
to <code title="dom-Event-BUBBLING_PHASE"><a href="#dom-event-bubbling_phase">BUBBLING_PHASE</a></code>. If an
<a href="#concept-event-listener" title="concept-event-listener">event listener</a> was registered for
the <code title="">span</code> <a href="#concept-element" title="concept-element">element</a>,
<code title="dom-Event-eventPhase"><a href="#dom-event-eventphase">eventPhase</a></code> attribute's value
would have been <code title="dom-Event-AT_TARGET"><a href="#dom-event-at_target">AT_TARGET</a></code>.
<h3 id="interface-event"><span class="secno">5.2 </span>Interface <code><a href="#event">Event</a></code></h3>
<pre class="idl">[<a href="#concept-event-constructor" title="concept-event-constructor">Constructor</a>(DOMString <var title="">type</var>, optional <a href="#eventinit">EventInit</a> <var title="">eventInitDict</var>)]
interface <dfn id="event">Event</dfn> {
readonly attribute DOMString <a href="#dom-event-type" title="dom-Event-type">type</a>;
readonly attribute <a href="#eventtarget">EventTarget</a>? <a href="#dom-event-target" title="dom-Event-target">target</a>;
readonly attribute <a href="#eventtarget">EventTarget</a>? <a href="#dom-event-currenttarget" title="dom-Event-currentTarget">currentTarget</a>;
const unsigned short <a href="#dom-event-none" title="dom-Event-NONE">NONE</a> = 0;
const unsigned short <a href="#dom-event-capturing_phase" title="dom-Event-CAPTURING_PHASE">CAPTURING_PHASE</a> = 1;
const unsigned short <a href="#dom-event-at_target" title="dom-Event-AT_TARGET">AT_TARGET</a> = 2;
const unsigned short <a href="#dom-event-bubbling_phase" title="dom-Event-BUBBLING_PHASE">BUBBLING_PHASE</a> = 3;
readonly attribute unsigned short <a href="#dom-event-eventphase" title="dom-Event-eventPhase">eventPhase</a>;
void <a href="#dom-event-stoppropagation" title="dom-Event-stopPropagation">stopPropagation</a>();
void <a href="#dom-event-stopimmediatepropagation" title="dom-Event-stopImmediatePropagation">stopImmediatePropagation</a>();
readonly attribute boolean <a href="#dom-event-bubbles" title="dom-Event-bubbles">bubbles</a>;
readonly attribute boolean <a href="#dom-event-cancelable" title="dom-Event-cancelable">cancelable</a>;
void <a href="#dom-event-preventdefault" title="dom-Event-preventDefault">preventDefault</a>();
readonly attribute boolean <a href="#dom-event-defaultprevented" title="dom-Event-defaultPrevented">defaultPrevented</a>;
[Unforgeable] readonly attribute boolean <a href="#dom-event-istrusted" title="dom-Event-isTrusted">isTrusted</a>;
readonly attribute DOMTimeStamp <a href="#dom-event-timestamp" title="dom-Event-timeStamp">timeStamp</a>;
void <a href="#dom-event-initevent" title="dom-Event-initEvent">initEvent</a>(DOMString <var title="">type</var>, boolean <var title="">bubbles</var>, boolean <var title="">cancelable</var>);
};
dictionary <dfn id="eventinit">EventInit</dfn> {
boolean <span title="dom-EventInit-bubbles">bubbles</span> = false;
boolean <span title="dom-EventInit-cancelable">cancelable</span> = false;
};</pre>
</p><p>An <dfn id="concept-event" title="concept-event">event</dfn> allows for signaling that
something has occurred. E.g. that an image has completed downloading. It is
represented by the <code><a href="#event">Event</a></code> interface or an interface that
inherits from the <code><a href="#event">Event</a></code> interface.</p>
<dl class="domintro">
<dt><code>var <var title="">event</var> = new <a href="#concept-event-constructor" title="concept-event-constructor">Event</a>(<var title="">type</var> [, <var title="">eventInitDict</var>])</code>
<dd><p>Returns a new <var title="">event</var> whose
<code title="dom-Event-type"><a href="#dom-event-type">type</a></code> attribute value is set to
<var title="">type</var>. The optional <var title="">eventInitDict</var> argument
allows for setting the <code title="dom-Event-bubbles"><a href="#dom-event-bubbles">bubbles</a></code> and
<code title="dom-Event-cancelable"><a href="#dom-event-cancelable">cancelable</a></code> attributes via object
members of the same name.
<dt><code><var title="">event</var> . <a href="#dom-event-type" title="dom-Event-type">type</a></code>
<dd><p>Returns the type of <var title="">event</var>, e.g.
"<code title="">click</code>", "<code title="">hashchange</code>", or
"<code title="">submit</code>".
<dt><code><var title="">event</var> . <a href="#dom-event-target" title="dom-Event-target">target</a></code>