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<!DOCTYPE html><html lang="en-US"><head>
<meta charset="UTF-8">
<title>
Presentation API
</title>
<style>
@media print {
[data-anolis-spec]::after { content:"[" attr(data-anolis-spec) "]"; font-size:.6em; vertical-align:super; text-transform:uppercase }
}
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED" rel="stylesheet" type="text/css">
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/* .example idl formatting taken from HTML5 nightly spec */
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dfn { font-weight: bolder; font-style: normal; }
#use-cases-and-requirements dd { margin-top: 0.5em; margin-bottom: 1em; }
.copyright { font-size: small; }
</style>
</head>
<body>
<div class="head">
<!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt="W3C" height="48" src="https://www.w3.org/Icons/w3c_home" width="72"></a></p>
<!--end-logo-->
<h1>
Presentation API
</h1>
<h2 class="no-num no-toc" id="editor's-draft-15-may-2015">
Editor's Draft 15 May 2015
</h2>
<dl>
<dt>
This version:
</dt>
<dd>
<!--begin-link--><a href="http://w3c.github.io/presentation-api/
">http://w3c.github.io/presentation-api/
</a><!--end-link-->
</dd>
<dt>
Latest published version:
</dt>
<dd>
<!--begin-link--><a href="http://www.w3.org/TR/presentation-api/
">http://www.w3.org/TR/presentation-api/
</a><!--end-link-->
</dd>
<dt>
Latest editor's draft:
</dt>
<dd>
<!--begin-link--><a href="http://w3c.github.io/presentation-api/
">http://w3c.github.io/presentation-api/
</a><!--end-link-->
</dd>
<dt>
Version history:
</dt>
<dd>
<!--begin-link--><a href="https://github.com/w3c/presentation-api/commits/
">https://github.com/w3c/presentation-api/commits/
</a><!--end-link-->
</dd>
<dt>
Participate:
</dt>
<dd>
Send feedback to <a href="https://lists.w3.org/Archives/Public/public-secondscreen/">public-secondscreen@w3.org</a>
or <a href="https://github.com/w3c/presentation-api/issues/new">open
a new issue</a> (<a href="https://github.com/w3c/presentation-api/issues/">open issues</a>)
</dd>
<dt>
Editors:
</dt>
<dd>
<a href="mailto:mfoltz@google.com">Mark Foltz</a>, Google
</dd>
<dd>
Dominik Röttsches, Intel (until April 2015)
</dd>
</dl>
<p class="copyright">
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
© 2015 <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>). 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/copyright-documents">document
use</a> rules apply.
</p>
<hr>
</div>
<section>
<h2 class="no-num no-toc" id="abstract">
Abstract
</h2>
<p>
This specification defines an API to enable web content to access
external presentation-type displays and use them for presenting web
content.
</p>
</section>
<section>
<h2 class="no-num no-toc" id="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 was published by the <a href="http://www.w3.org/2014/secondscreen/">Second Screen Presentation
Working Group</a> as an Editor's Draft. If you wish to make comments
regarding this document, please send them to <a href="mailto:public-secondscreen@w3.org">public-secondscreen@w3.org</a>
(<a href="mailto:public-secondscreen-request@w3.org?subject=subscribe">subscribe</a>,
<a href="http://lists.w3.org/Archives/Public/public-secondscreen/">archives</a>).
All comments are welcome.
</p>
<p>
This document is a <b>work in progress</b> and is subject to change. It
builds on the <a href="http://www.w3.org/2014/secondscreen/presentation-api/20141118/" title="Presentation API W3C Community Group Final Report">final report</a>
(dated 18 November 2014) produced by the Second Screen Presentation
Community Group. Algorithms have been drafted in particular. Most
sections are still incomplete or underspecified. Privacy and security
considerations are missing. A few open issues are noted inline. Please
check the group's <a href="https://github.com/w3c/presentation-api/issues">issue tracker</a> on
GitHub for an accurate list. Feedback from early experimentations is
encouraged to allow the Second Screen Presentation Working Group to
evolve the specification based on implementation issues.
</p>
<p>
Publication as a First Public Working Draft does not imply endorsement
by the <abbr title="World Wide Web Consortium">W3C</abbr> Membership.
This draft document 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 href="http://www.w3.org/Consortium/Patent-Policy-20040205/" id="sotd_patent" rel="w3p:patentRules">5 February 2004
<abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>.
<abbr title="World Wide Web Consortium">W3C</abbr> maintains a <a href="http://www.w3.org/2004/01/pp-impl/74168/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 that 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 <abbr title="World Wide Web Consortium">W3C</abbr> Patent
Policy</a>.
</p>
<p>
This document is governed by the <a href="http://www.w3.org/2014/Process-20140801/" id="w3c_process_revision">1 August 2014 <abbr title="World Wide Web Consortium">W3C</abbr> Process Document</a>.
</p>
</section>
<section>
<h2 class="no-num no-toc" id="table-of-contents">
Table of Contents
</h2>
<!--begin-toc-->
<ol class="toc">
<li><a href="#introduction"><span class="secno">1 </span>
Introduction
</a></li>
<li><a href="#use-cases-and-requirements-0"><span class="secno">2 </span>
Use cases and requirements
</a>
<ol>
<li><a href="#use-cases-0"><span class="secno">2.1 </span>
Use cases
</a></li>
<li><a href="#requirements-0"><span class="secno">2.2 </span>
Requirements
</a>
<ol>
<li><a href="#functional-requirements"><span class="secno">2.2.1 </span>
Functional requirements
</a></li>
<li><a href="#non-functional-requirements"><span class="secno">2.2.2 </span>
Non-functional requirements
</a></ol></ol></li>
<li><a href="#conformance"><span class="secno">3 </span>
Conformance
</a></li>
<li><a href="#terminology"><span class="secno">4 </span>
Terminology
</a></li>
<li><a href="#examples"><span class="secno">5 </span>
Examples
</a>
<ol>
<li><a href="#monitor-availability-of-presentation-displays-example"><span class="secno">5.1 </span>
Monitor availability of presentation displays example
</a></li>
<li><a href="#starting-a-new-presentation-session-example"><span class="secno">5.2 </span>
Starting a new presentation session example
</a></li>
<li><a href="#joining-a-presentation-session-example"><span class="secno">5.3 </span>
Joining a presentation session example
</a></li>
<li><a href="#handling-an-event-for-a-ua-initiated-presentation-session-example"><span class="secno">5.4 </span>
Handling an event for a UA initiated presentation session example
</a></li>
<li><a href="#monitor-session's-state-and-exchange-data-example"><span class="secno">5.5 </span>
Monitor session's state and exchange data example
</a></ol></li>
<li><a href="#specifying-the-default-presentation-url-and-id."><span class="secno">6 </span>
Specifying the default presentation URL and id.
</a></li>
<li><a href="#api"><span class="secno">7 </span>
API
</a>
<ol>
<li><a href="#common-idioms"><span class="secno">7.1 </span>
Common idioms
</a></li>
<li><a href="#common-definitions"><span class="secno">7.2 </span>
Common definitions
</a></li>
<li><a href="#interface-presentationsession"><span class="secno">7.3 </span>
Interface <code>PresentationSession</code>
</a>
<ol>
<li><a href="#sending-a-message-through-presentationsession"><span class="secno">7.3.1 </span>
Sending a message through <code>PresentationSession</code>
</a></li>
<li><a href="#receiving-a-message-through-presentationsession"><span class="secno">7.3.2 </span>
Receiving a message through <code>PresentationSession</code>
</a></li>
<li><a href="#closing-a-presentationsession"><span class="secno">7.3.3 </span>
Closing a <code>PresentationSession</code>
</a></li>
<li><a href="#event-handlers"><span class="secno">7.3.4 </span>
Event Handlers
</a></ol></li>
<li><a href="#interface-navigatorpresentation"><span class="secno">7.4 </span>
Interface <code>NavigatorPresentation</code>
</a>
<ol>
<li><a href="#starting-a-presentation-session"><span class="secno">7.4.1 </span>
Starting a presentation session
</a></li>
<li><a href="#initiating-the-presentation-session-by-the-user-agent"><span class="secno">7.4.2 </span>
Initiating the presentation session by the user agent
</a></li>
<li><a href="#joining-a-presentation-session"><span class="secno">7.4.3 </span>
Joining a presentation session
</a></li>
<li><a href="#establishing-a-presentation-connection"><span class="secno">7.4.4 </span>
Establishing a presentation connection
</a></li>
<li><a href="#the-onavailablechange-eventhandler"><span class="secno">7.4.5 </span>
The <code>onavailablechange</code> EventHandler
</a>
<ol>
<li><a href="#adding-an-eventhandler-to-onavailablechange"><span class="secno">7.4.5.1 </span>
Adding an <code>EventHandler</code> to
<code>onavailablechange</code>
</a></li>
<li><a href="#removing-an-eventhandler"><span class="secno">7.4.5.2 </span>
Removing an <code>EventHandler</code>
</a></li>
<li><a href="#monitoring-the-list-of-available-presentation-displays"><span class="secno">7.4.5.3 </span>
Monitoring the list of available presentation displays
</a></ol></ol></li>
<li><a href="#interface-availablechangeevent"><span class="secno">7.5 </span>
<span>Interface <code>AvailableChangeEvent</code></span>
</a></li>
<li><a href="#interface-defaultsessionstart"><span class="secno">7.6 </span>
<span>Interface <code>DefaultSessionStart</code></span>
</a></ol></li>
<li><a href="#security-and-privacy-considerations"><span class="secno">8 </span>
Security and privacy considerations
</a></li>
<li><a href="#references"><span class="secno">9 </span>
References
</a></li>
<li><a href="#acknowledgments"><span class="secno">10 </span>
Acknowledgments
</a></ol>
<!--end-toc-->
</section>
<section>
<h2 id="introduction"><span class="secno">1 </span>
Introduction
</h2><em>This section is non-normative.</em>
<p>
This specification aims to make secondary displays such as a projector
or a connected TV available to the web and takes into account displays
that are attached using wired (HDMI, DVI or similar) and wireless
technologies (MiraCast, Chromecast, DLNA, AirPlay or similar).
</p>
<p>
Devices with limited screen size lack the ability to show content to a
larger audience, for example, a group of colleagues in a conference
room, or friends and family at home. Showing content on an external
large display helps to improve the perceived quality and impact of the
presented content.
</p>
<p>
At its core, this specification enables an exchange of messages between
a requesting page and a presentation page shown in the secondary
display. How those messages are transmitted is left to the UA in order
to allow for the use of display devices that can be attached to a wide
variety of ways. For example, when a display device is attached using
HDMI or MiraCast, the UA on the requesting device can render the
requested presentation page in that same UA. Instead of displaying in a
window on that same device, however, it can use whatever means the
operating system provides for using those external displays. In that
case, both the requesting page and the presentation page run on the
requesting device and the operating system is used to route the
presentation display output to the other display device. The second
display device doesn't need to know anything about this spec or that
the content involves HTML5.
</p>
<p>
Alternately, some types of external displays may be able to render
HTML5 themselves and may have defined their way to send messages to
that content. In that case, the UA on the requesting device would not
need to render the presentation page itself. Instead, the UA could act
as a proxy translating the request to show a page and the messages into
the form understood by the display device.
</p>
<p>
This way of attaching to displays could be enhanced in the future by
defining a standard protocol for delivering these types of messages
that display devices could choose to implement.
</p>
<p>
The API defined here is intended to be used with UAs that attach to
display devices through any of the above means.
</p>
</section>
<section id="use-cases-and-requirements">
<h2 id="use-cases-and-requirements-0"><span class="secno">2 </span>
Use cases and requirements
</h2>
<section id="use-cases">
<h3 id="use-cases-0"><span class="secno">2.1 </span>
Use cases
</h3>
<dl>
<dt>
Presentations
</dt>
<dd>
A user is preparing a set of slides for a talk. Using a web-based
service, she is editing her slides and speaker notes on the primary
screen while the secondary larger screen shows a preview of the
current slide. When the slides are done, her mobile phone allows
her to access them from an online service while on the go. Coming
to the conference, using wireless display technology, she would
like to present her slides on the stage screen from her mobile
phone. The phone's touch screen helps her to navigate slides and
presents a slide preview while the projector shows her slides to
the audience.
</dd>
<dt>
Video and image sharing
</dt>
<dd>
Using an online video or image sharing service, a user would like
to show memorable moments to her friends. Using a device with a
small screen, however, a user cannot show the content to a large
group of people. Connecting an external TV screen or projector to
her device - with a cable or wirelessly - the online sharing
service now makes use of the connected display, allowing a wider
audience to enjoy the content. The web page shows UI elements that
allow the user to trigger displaying content on the secondary
display (e.g., a "send to second screen" ) only if there is at
least one secondary screen available.
</dd>
<dt>
Multiplayer gaming
</dt>
<dd>
Splitting the gaming experience into a near screen controller and a
large screen visual experience can create new gaming experiences.
Accessing the local display on the small screen device and an
external larger display allows for richer web-based gaming
experiences.
<p class="open-issue">
<a href="https://github.com/w3c/presentation-api/issues/27">ISSUE
27: Define a multiplayer gaming use case</a>
</p>
</dd>
<dt>
Media flinging to multiple screens
</dt>
<dd>
Alice enters a video sharing site using a browser on her tablet.
Next, Alice picks her favorite video from the site, and the video
starts to play on her tablet. While the video is playing Alice
clicks a button "Share on different screen". The browser provides a
user interface that lists all the screens Alice has at her home,
asking her to select one. The screens are identified by names that
are familiar to Alice. Alice picks one screen from the list,
"Alice's big TV", and the video playback continues seamlessly on
the selected screen. Next she decides to switch the playback to a
different screen. She clicks the same button "Share on different
screen" provided by the site, and the browser presents the user
interface that lists all the screens. Alice picks another screen
from the list, "Alice's kitchen TV", and the playback resumes on
that screen. Video site also provides a feature to see the action
(Alice is watching a soccer game) from a different angle. Alice
clicks a button "Select screen for additional angle", and the
browser asks Alice similarly to select the screen for playback.
Alice picks "Alice's Projector" and the soccer game is shown on the
projector from a different angle, in parallel to the content being
played back on "Alice's kitchen TV".
<p class="open-issue">
<a href="https://github.com/w3c/presentation-api/issues/40">ISSUE
40: Screen availability mechanism for multiple sessions</a>
</p>
</dd>
</dl>
</section>
<section id="requirements">
<h3 id="requirements-0"><span class="secno">2.2 </span>
Requirements
</h3>
<p>
The requirements enumerated in this section are derived from the
<a href="#use-cases">use cases</a>.
</p>
<section>
<h4 id="functional-requirements"><span class="secno">2.2.1 </span>
Functional requirements
</h4>
<dl>
<dt>
Discovery & availability
</dt>
<dd>
The UA must provide a way to find out whether at least one
secondary screen is available.
</dd>
<dt>
Launching presentation
</dt>
<dd>
The UA must provide a way to start sending content to the
secondary screen. This may occur at the request of the page or at
the request of the UA.
</dd>
<dt>
Resuming presentation
</dt>
<dd>
The UA must be able to resume an existing session with the
content being displayed on the secondary screen.
</dd>
<dt>
Communication
</dt>
<dd>
The UA must enable exchanging data between the primary and the
secondary screen in order to have a control channel between the
primary and secondary page. The UA must not make assumptions
about the execution locality of the UA of the remote page it
communicates with (i.e. the secondary page might run on a remote
UA, and thus the link between these two pages must be loosely
coupled).
</dd>
<dt>
Signaling disconnection
</dt>
<dd>
The UA must signal disconnection from the presentation page to
the primary page and vice versa.
</dd>
</dl>
<p class="note">
Multi-screen enumeration and named identification requirement was
removed after <a class="external free" href="http://lists.w3.org/Archives/Public/public-webscreens/2014Feb/0021.html" rel="nofollow">
discussion on the mailing list</a>.
</p>
</section>
<section>
<h4 id="non-functional-requirements"><span class="secno">2.2.2 </span>
Non-functional requirements
</h4>
<dl>
<dt>
Power saving friendly
</dt>
<dd>
All API design decisions must be analyzed from a power efficiency
point of view. Especially when using wireless display
technologies or querying availability over a radio channel, care
needs to be taken to design the API in a way that does not pose
obstacles to using radio resources in an efficient way. For
example, powering up the wireless display detection only when
needed.
</dd>
</dl>
</section>
</section>
</section>
<section>
<h2 id="conformance"><span class="secno">3 </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 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>
</section>
<section>
<h2 id="terminology"><span class="secno">4 </span>
Terminology
</h2>
<p>
The terms <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/browsers.html#browsing-context">browsing context</a>,
<a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/webappapis.html#event-handlers">event handlers</a>, <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/webappapis.html#event-handler-event-type" title="event handler event type">event handler
event types</a>, <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/infrastructure.html#concept-event-fire" title="concept-event-fire">firing an event</a>, <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/browsers.html#navigate">navigate</a>, <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/webappapis.html#queue-a-task" title="queue a task">queing a task</a>, <span>link elements</span> are
defined in <a href="#refsHTML5">[HTML5]</a>.
</p>
<p>
The term <a class="external" data-anolis-spec="dom" href="https://dom.spec.whatwg.org/#domexception" title="domexception">DOMException</a> is defined in <a href="#refsDOM">[DOM]</a>.
</p>
<p>
The term <a class="external" data-anolis-spec="es6" href="https://people.mozilla.org/~jorendorff/es6-draft.html#sec-promise-objects" title="promise-objects">Promise</a> is defined in <a href="#refsES6">[ES6]</a>. The terms <a class="external" data-anolis-spec="promguide" href="http://www.w3.org/2001/tag/doc/promises-guide#shorthand-manipulating" title="resolve-reject">resolving a Promise, and rejecting a Promise</a>
are used as explained in <a href="#refsPROMGUIDE">[PROMGUIDE]</a>.
</p>
<p>
The term <a class="external" data-anolis-spec="url" href="https://url.spec.whatwg.org/#url">URL</a> is defined in the
WHATWG URL standard: <a href="#refsURL">[URL]</a>.
</p>
<p>
The terms <a class="external" data-anolis-spec="typedarray" href="http://www.khronos.org/registry/typedarray/specs/latest/#5">ArrayBuffer</a>,
<a class="external" data-anolis-spec="typedarray" href="http://www.khronos.org/registry/typedarray/specs/latest/#6">ArrayBufferView</a> are defined
in the Typed Array specification: <a href="#refsTYPEDARRAY">[TYPEDARRAY]</a>.
</p>
<p>
The term <a class="external" data-anolis-spec="fileapi" href="http://dev.w3.org/2006/webapi/FileAPI/#blob">Blob</a> is defined in the
File API specification: <a href="#refsFILEAPI">[FILEAPI]</a>.
</p>
<p>
This document provides interface definitions using the
<a href="#refsWEBIDL">[WEBIDL]</a> standard.
</p>
</section>
<section>
<h2 id="examples"><span class="secno">5 </span>
Examples
</h2>
<p class="open-issue">
<a href="https://github.com/w3c/presentation-api/issues/42">ISSUE 42:
Make the Example section more concise</a>
</p>
<p>
This section shows example codes that highlight the usage of main
features of the Presentation API. In these examples,
<code>controller.html</code> represents the controlling page that runs
in the opener UA and <code>presentation.html</code> represents the
presenting page that runs in the presenting UA. Both pages are served
from the domain <code>http://example.org</code>
(<code>http://example.org/controller.html</code> and
<code>http://example.org/presentation.html</code>). Please refer to the
comments in the code examples for further details.
</p>
<section>
<h3 id="monitor-availability-of-presentation-displays-example"><span class="secno">5.1 </span>
Monitor availability of presentation displays example
</h3>
<pre class="example"><!-- controller.html -->
<button id="castBtn" style="display: none;">Cast</button>
<script>
// the cast button is visible if at least one presentation display is available
var castBtn = document.getElementById("castBtn");
// availablechange event is fired when the presentation display availability changes
navigator.presentation.onavailablechange = function (evt) {
// show or hide cast button depending on display availability
castBtn.style.display = evt.available ? "inline" : "none";
};
</script>
</pre>
</section>
<section>
<h3 id="starting-a-new-presentation-session-example"><span class="secno">5.2 </span>
Starting a new presentation session example
</h3>
<pre class="example"><!-- controller.html -->
<script>
// it is also possible to use relative presentation URL e.g. "presentation.html"
var presUrl = "http://example.com/presentation.html";
// create random presId
var presId = Math.random().toFixed(6).substr(2);
// Start new session. presId is optional.
navigator.presentation.startSession(presUrl, presId)
// the new started session will be passed to setSession on success
.then(setSession)
// user cancels the selection dialog or an error is occurred
.catch(endSession);
</script>
</pre>
</section>
<section>
<h3 id="joining-a-presentation-session-example"><span class="secno">5.3 </span>
Joining a presentation session example
</h3>
<pre class="example"><!-- controller.html -->
<script>
// read presId from localStorage if exists
var presId = localStorage && localStorage["presId"] || null;
// presId is mandatory for joinSession.
presId && navigator.presentation.joinSession(presUrl, presId)
// The joined session will be passed to setSession on success
.then(setSession)
// no session found for presUrl and presId or an error is occurred
.catch(endSession);
</script>
</pre>
</section>
<section>
<h3 id="handling-an-event-for-a-ua-initiated-presentation-session-example"><span class="secno">5.4 </span>
Handling an event for a UA initiated presentation session example
</h3>
<pre class="example"><!-- controller.html -->
<head>
<!-- the link element with rel='default-presentation' allows the page to specify -->
<!-- the presentation URL and id for when the UA initiates a presentation session -->
<link href="http://example.com/presentation.html" rel="default-presentation" id="ABCD1234" >
</head>
<script>
navigator.presentation.ondefaultsessionstart = function (evt) {
setSession(evt.session);
};
</script>
</pre>
</section>
<section>
<h3 id="monitor-session's-state-and-exchange-data-example"><span class="secno">5.5 </span>
Monitor session's state and exchange data example
</h3>
<pre class="example"><!-- controller.html -->
<script>
var session;
var setSession = function (theSession) {
// end existing session, if any
endSession();
// set the new session
session = theSession;
if (session) {
// save presId in localStorage
localStorage && (localStorage["presId"] = session.id);
// monitor session's state
session.onstatechange = function () {
if (this == session && this.state == "disconnected")
endSession();
};
// register message handler
session.onmessage = function (evt) {
console.log("receive message", evt.data);
};
// send message to presentation page
session.send("say hello");
}
};
var endSession = function () {
// close old session if exists
session && session.close();
// remove old presId from localStorage if exists
localStorage && delete localStorage["presId"];
};
</script>
</pre>
<pre class="example"><!-- presentation.html -->
<script>
var session = navigator.presentation.session;
session.onstatechange = function () {
// session.state is either 'connected' or 'disconnected'
console.log("session's state is now", session.state);
};
session.onmessage = function (evt) {
if (evt.data == "say hello")
session.send("hello");
};
</script>
</pre>
</section>
</section>
<section>
<h2 id="specifying-the-default-presentation-url-and-id."><span class="secno">6 </span>
Specifying the default presentation URL and id.
</h2>
<p>
The <code>default-presentation</code> keyword can be used with a
<a href="#refsHTML5">[HTML5]</a> <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/semantics.html#the-link-element" title="link">link element</a>. This keyword allows to specify the
URL to use by the UA when the UA initiates a <a href="#concept-presentation" title="concept-presentation">presentation</a>. An optional <a href="#id"><code>id</code></a>
attribute also allows specifying a <a href="#presentation-session-identifier">presentation session
identifier</a> to use for the UA initiated <a href="#concept-presentation" title="concept-presentation">presentation</a>.
</p>
<table border="1">
<tr>
<th rowspan="2">
Link type
</th>
<th colspan="2">
Effect on...
</th>
<th rowspan="2">
Brief description
</th>
</tr>
<tr>
<th>
<code>link</code>
</th>
<th>
<code><a title="a element">a</a></code> and <code><a title="area element">area</a></code>
</th>
</tr>
<tr>
<td>
<code><dfn id="rel-default-presentation" title="rel-default-presentation">default-presentation</dfn></code>
</td>
<td>
<a title="external resource link">External Resource</a>
</td>
<td>
not allowed
</td>
<td>
Links to a <span>presentation url</span>.
</td>
</tr>
</table>
<p class="note">
In cases where more than one <a><code>link</code> element</a> with a
<code>default-presentation</code> link type appears in a
<code>Document</code>, the user agent uses the first
<a><code>link</code> element</a> in tree order and ignores all
subsequent <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/semantics.html#the-link-element" title="link">link
element</a> with a <code>default-presentation</code> link type (even
if the first element was erroneous).
</p>
<p>
The <span>default presentation URL</span> may be used by the UA to
filter the available screens while <a href="#algorithm-monitor-available" title="algorithm-monitor-available">monitoring the list of available
presentation displays</a>.
</p>
</section>
<section>
<h2 id="api"><span class="secno">7 </span>
API
</h2>
<section>
<h3 id="common-idioms"><span class="secno">7.1 </span>
Common idioms
</h3>
<p>
A <dfn id="presentation-display">presentation display</dfn> refers to an external screen
available to the user agent via an implementation specific connection
technology.
</p>
<p>
A <dfn id="concept-presentation" title="concept-presentation">presentation</dfn> is an active
connection between a user agent and a <a href="#presentation-display">presentation
display</a> for displaying web content on the latter at the
request of the former.
</p>
<p>
A <dfn id="concept-presentation-session" title="concept-presentation-session">presentation
session</dfn> is an object relating an <a href="#opening-browsing-context">opening browsing
context</a> to its <a href="#presentation-display">presentation display</a> and enabling
two-way-messaging between them. Each such object has a
<dfn id="presentation-session-state">presentation session state</dfn> and a <dfn id="presentation-session-identifier">presentation session
identifier</dfn> to distinguish it from other <a href="#concept-presentation-session" title="concept-presentation-session">presentation sessions</a>.
</p>
<p>
An <dfn id="opening-browsing-context">opening browsing context</dfn> is a <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/browsers.html#browsing-context">browsing context</a> that has initiated or resumed a
<span>presentation session</span> by calling
<code><a href="#startsession">startSession</a>()</code> or
<code><a href="#joinsession">joinSession</a>()</code> or received a
<span>presentation session</span> via
<code><span>ondefaultsessionstart</span></code> event.
</p>
<p>
The <dfn id="presenting-browsing-context">presenting browsing context</dfn> is the browsing context
responsible for rendering to a <a href="#presentation-display">presentation display</a>. A
<a href="#presenting-browsing-context">presenting browsing context</a> can reside in the same user
agent as the <a href="#opening-browsing-context">opening browsing context</a> or a different
one.
</p>
</section>
<section>
<h3 id="common-definitions"><span class="secno">7.2 </span>
Common definitions
</h3>
<p>
Let <em>D</em> be the set of presentations that are currently known
to the user agent (regardles of their state). <em>D</em> is
represented as a set of tuples <em>(U, I, S)</em> where <em>U</em> is
the <a class="external" data-anolis-spec="url" href="https://url.spec.whatwg.org/#url">URL</a> that is being presented;
<em>I</em> is an alphanumeric identifier for the presentation; and
<em>S</em> is the user agent's <a href="#presentationsession"><code>PresentationSession</code></a> for
the presentation. <em>U</em> and <em>I</em> together uniquely
identify the <a href="#presentationsession"><code>PresentationSession</code></a> of the corresponding
presentation.
</p>
</section>
<section>
<h3 id="interface-presentationsession"><span class="secno">7.3 </span>
Interface <a href="#presentationsession"><code>PresentationSession</code></a>
</h3>
<p>
Each <a href="#concept-presentation-session" title="concept-presentation-session">presentation
session</a> is represented by a <a href="#presentationsession"><code>PresentationSession</code></a>
object.
</p>
<pre class="idl">enum <dfn id="presentationsessionstate">PresentationSessionState</dfn> { "connected", "disconnected" /*, "resumed" */ };
enum <dfn id="binarytype">BinaryType</dfn> { "blob", "arraybuffer" };
interface <dfn id="presentationsession">PresentationSession</dfn> : EventTarget {
readonly <a class="external" data-anolis-spec="webidl" href="http://heycam.github.io/webidl/#idl-DOMString">DOMString</a>? <a href="#id">id</a>;
readonly attribute <a href="#presentationsessionstate">PresentationSessionState</a> <a href="#state">state</a>;
void <a href="#close">close</a>();
attribute <a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/webappapis.html#eventhandler">EventHandler</a> <a href="#onstatechange">onstatechange</a>;
// Communication
attribute BinaryType <dfn id="binarytype-attribute" title="binarytype-attribute">binaryType</dfn>;
<a class="external" data-anolis-spec="w3c-html" href="http://www.w3.org/html/wg/drafts/html/master/webappapis.html#eventhandler">EventHandler</a> <dfn id="presentation-onmessage" title="presentation-onmessage">onmessage</dfn>;
void <dfn id="send">send</dfn> (<a class="external" data-anolis-spec="webidl" href="http://heycam.github.io/webidl/#idl-DOMString">DOMString</a> message);
void <dfn id="send-blob" title="send-blob">send</dfn> (<a class="external" data-anolis-spec="fileapi" href="http://dev.w3.org/2006/webapi/FileAPI/#blob">Blob</a> data);
void <dfn id="send-arraybuffer" title="send-arraybuffer">send</dfn> (<a class="external" data-anolis-spec="typedarray" href="http://www.khronos.org/registry/typedarray/specs/latest/#5">ArrayBuffer</a> data);
void <dfn id="send-arraybufferview" title="send-arraybufferview">send</dfn> (<a class="external" data-anolis-spec="typedarray" href="http://www.khronos.org/registry/typedarray/specs/latest/#6">ArrayBufferView</a> data);
};
</pre>
<p>
The <dfn id="id"><code>id</code></dfn> attribute holds the alphanumeric
<a href="#presentation-session-identifier">presentation session identifier</a>.
</p>
<p>
The <dfn id="state"><code>state</code></dfn> attribute represents the
<span>presentation session</span>'s current state. It can take one of
the values of <a href="#presentationsessionstate"><code>PresentationSessionState</code></a>
depending on connection state.
</p>
<p>
When the <code><a href="#send">send</a>()</code> method is called on a
<a href="#presentationsession"><code>PresentationSession</code></a> object with a <code>message</code>,
the user agent must run the algorithm to <a href="#algorithm-send" title="algorithm-send">send a message through a
<span><code>PresentationSession</code></span></a>.
</p>
<p>
When the <code><dfn id="close">close</dfn>()</code> method is called on a
<a href="#presentationsession"><code>PresentationSession</code></a>, the user agent must run the
algorithm to <a href="#close-algorithm" title="close-algorithm">close a presentation
session</a>.
</p>
<p class="open-issue">
<a href="https://github.com/w3c/presentation-api/issues/34">ISSUE 34:
Specify the presentation initialization algorithm</a>
</p>
<section>
<p class="open-issue">
<a href="https://github.com/w3c/presentation-api/issues/46">ISSUE
46: Define send behavior</a>
</p>
<h4 id="sending-a-message-through-presentationsession"><span class="secno">7.3.1 </span>
Sending a message through <a href="#presentationsession"><code>PresentationSession</code></a>
</h4>
<p class="note">
Presentation API does not mandate a specific protocol for the
connection between the <a href="#opening-browsing-context">opening browsing context</a> and
the <a href="#presenting-browsing-context">presenting browsing context</a> except that for
multiple calls to <a href="#send"><code>send</code></a> it has to be ensured that
messages are delivered to the other end in sequence.
</p>
<p>
Let <dfn id="presentation-message-data">presentation message data</dfn> be the payload data to be
transmitted between two browsing contexts. Let <dfn id="presentation-message-type">presentation
message type</dfn> be the type of that data, one of
<code>text</code> and <code>binary</code>.
</p>
<p>
When the user agent is to <dfn id="algorithm-send" title="algorithm-send">send a
message through a <code>PresentationSession</code> S</dfn>, it must
run the following steps:
</p>
<ol>
<li>If the <a href="#state"><code>state</code></a> property of
<a href="#presentationsession"><code>PresentationSession</code></a> is <code>"disconnected"</code>,
throw an <code>InvalidStateError</code> exception.
</li>
<li>Let <a href="#presentation-message-type">presentation message type</a> <em>messageType</em>
be <code>binary</code> if <code>data</code> is one of
<code>ArrayBuffer</code> or <code>Blob</code>. Let
<em>messageType</em> be <code>text</code> if <code>data</code> is
of type <code>DOMString</code>)
</li>
<li>Assign the <dfn id="destination-browsing-context">destination browsing context</dfn> as follows:
<ol>
<li>Let the the <a href="#destination-browsing-context">destination browsing context</a> be
the <a href="#opening-browsing-context">opening browsing context</a> if <a href="#send">send</a>
is called in the <a href="#presenting-browsing-context">presenting browsing context</a>.
</li>
<li>Let <a href="#destination-browsing-context">destination browsing context</a> be the <a href="#presenting-browsing-context">
presenting browsing context</a> if <a href="#send">send</a> is
called from the <a href="#opening-browsing-context">opening browsing context</a>.
</li>
</ol>
</li>
<li>Using an implementation specific mechanism, transmit the
contents of the <code>data</code> argument as <a href="#presentation-message-data">presentation
message data</a> and <a href="#presentation-message-type">presentation message type</a> <em>
messageType</em> to the <a href="#destination-browsing-context">destination browsing context</a>
side.
</li>
</ol>
</section>
<section>
<h4 id="receiving-a-message-through-presentationsession"><span class="secno">7.3.2 </span>
Receiving a message through <a href="#presentationsession"><code>PresentationSession</code></a>
</h4>
<p>
When the user agent has received a transmission from the remote
side consisting of <a href="#presentation-message-data">presentation message data</a> and
<a href="#presentation-message-type">presentation message type</a>, it must run the following
steps:
</p>
<ol>
<li>If the <a href="#state"><code>state</code></a> property of
<a href="#presentationsession"><code>PresentationSession</code></a> is <code>"disconnected"</code>,
abort these steps.