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-
- <body><div class="head">
- <p>
-
- <a href="http://www.w3.org/"><img src="http://www.w3.org/Icons/w3c_home" alt="W3C" height="48" width="72"></a>
-
- </p>
- <h1 class="title" id="title">The Network Information API</h1>
-
- <h2 id="w3c-working-draft-23-november-2012"><abbr title="World Wide Web Consortium">W3C</abbr> Working Draft 23 November 2012</h2>
- <dl>
-
- <dt>This version:</dt>
- <dd><a href="http://www.w3.org/TR/2012/WD-netinfo-api-20121123/">http://www.w3.org/TR/2012/WD-netinfo-api-20121123/</a></dd>
- <dt>Latest published version:</dt>
- <dd><a href="http://www.w3.org/TR/netinfo-api/">http://www.w3.org/TR/netinfo-api/</a></dd>
-
-
- <dt>Latest editor's draft:</dt>
- <dd><a href="http://dvcs.w3.org/hg/dap/raw-file/tip/network-api/Overview.html">http://dvcs.w3.org/hg/dap/raw-file/tip/network-api/Overview.html</a></dd>
-
-
-
-
-
- <dt>Previous version:</dt>
- <dd><a href="http://www.w3.org/TR/2011/WD-netinfo-api-20110607/">http://www.w3.org/TR/2011/WD-netinfo-api-20110607/</a></dd>
-
-
- <dt>Editor:</dt>
- <dd><span>Mounir Lamouri</span>, <a href="http://mozilla.org/">Mozilla</a></dd>
-
-
- </dl>
-
-
-
-
-
- <p class="copyright">
- <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> ©
- 2012
-
- <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>), All Rights Reserved.
- <abbr title="World Wide Web Consortium">W3C</abbr> <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 class="introductory" id="abstract"><h2>Abstract</h2><p>
- The Network Information API provides an interface for web applications to
- access the underlying connection information of the device.
- </p></section><section id="sotd" class="introductory"><h2>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 <abbr title="World Wide Web Consortium">W3C</abbr> publications and the latest revision
- of this technical report can be found in the <a href="http://www.w3.org/TR/"><abbr title="World Wide Web Consortium">W3C</abbr> technical reports
- index</a> at http://www.w3.org/TR/.</em>
- </p>
-
- <p>
- The functionality described in this specification was initially specified as part of the
- <a href="http://www.w3.org/TR/system-info-api/">System Information API</a> but has been
- extracted in order to be more readily available, more straightforward to implement, and
- in order to produce a specification that could be implemented on its own merits without
- interference with other, often unrelated, features.
- </p>
-
- <p>
- This document was published by the <a href="http://www.w3.org/2009/dap/">Device APIs and Policy Working Group</a> as a Working Draft.
-
- This document is intended to become a <abbr title="World Wide Web Consortium">W3C</abbr> Recommendation.
-
- If you wish to make comments regarding this document, please send them to
- <a href="mailto:public-device-apis@w3.org">public-device-apis@w3.org</a>
- (<a href="mailto:public-device-apis-request@w3.org?subject=subscribe">subscribe</a>,
- <a href="http://lists.w3.org/Archives/Public/public-device-apis/">archives</a>).
-
-
- All feedback is welcome.
- </p>
-
- <p>
- Publication as a Working Draft does not imply endorsement by the <abbr title="World Wide Web Consortium">W3C</abbr> 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 href="http://www.w3.org/Consortium/Patent-Policy-20040205/">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/43696/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 <abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>.
-
-
- </p>
-
-
-
-
-</section><section id="toc"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a class="tocxref" href="#introduction"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#use-cases"><span class="secno">1.1 </span>Use Cases</a></li><li class="tocline"><a class="tocxref" href="#outstanding-issues"><span class="secno">1.2 </span>Outstanding issues</a></li></ul></li><li class="tocline"><a class="tocxref" href="#conformance"><span class="secno">2. </span>Conformance</a></li><li class="tocline"><a class="tocxref" href="#terminology"><span class="secno">3. </span>Terminology</a></li><li class="tocline"><a class="tocxref" href="#security-and-privacy-considerations"><span class="secno">4. </span>Security and privacy considerations</a></li><li class="tocline"><a class="tocxref" href="#the-networkinformation-interface"><span class="secno">5. </span>The <span class="formerLink"><code>NetworkInformation</code></span> interface</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#attributes"><span class="secno">5.1 </span>Attributes</a></li></ul></li><li class="tocline"><a class="tocxref" href="#the-connection-interface"><span class="secno">6. </span>The <span class="formerLink"><code>Connection</code></span> interface</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#attributes-1"><span class="secno">6.1 </span>Attributes</a></li><li class="tocline"><a class="tocxref" href="#event-handlers"><span class="secno">6.2 </span>Event handlers</a></li></ul></li><li class="tocline"><a class="tocxref" href="#examples"><span class="secno">7. </span>Examples</a></li><li class="tocline"><a class="tocxref" href="#acknowledgments"><span class="secno">A. </span>Acknowledgments</a></li><li class="tocline"><a class="tocxref" href="#references"><span class="secno">B. </span>References</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#normative-references"><span class="secno">B.1 </span>Normative references</a></li></ul></li></ul></section>
-
-
-
- <section id="introduction" class="informative">
- <!--OddPage--><h2><span class="secno">1. </span>Introduction</h2><p><em>This section is non-normative.</em></p>
- <p>
- The Network Information API provides an interface enabling web applications to access the underlying
- connection information of the device.
- </p>
-
- <section id="use-cases">
- <h3><span class="secno">1.1 </span>Use Cases</h3><p><em>This section is non-normative.</em></p>
- <p>
- The main use case of the Network Information API is to allow
- applications to be gentle with the user's bandwidth when they know it
- is rare or expensive. Even if there are not many applications that do
- this currently, this specification offers the the tools needed to
- enable this, allowing it to become more common.
- </p>
- <p>
- A few hypothetical examples would be:
- </p><ul>
- <li>An image viewer showing very low resolution thumbnails when the
- user has a low bandwidth or a metered connection.
- </li><li>A video game loading low textures when the user has a low
- bandwidth or a metered connection.</li>
- <li>An email client downloading only headers or even asking the user
- to download headers when he/she has a low bandwidth or a metered
- connection.</li>
- <li>Any app trying to aggressively cache any downloaded asset when
- the user has a low bandwidth or a metered connection.</li>
- </ul>
- <p></p>
- </section>
-
- <section id="outstanding-issues">
- <h3><span class="secno">1.2 </span>Outstanding issues</h3>
- <p>
- The specification currently requests the <a class="internalDFN" href="#dfn-user-agent">user agent</a> to expose
- two properties: <code>bandwidth</code> and <code>metered</code>. The
- working group currently does not have consensus on these.
- </p>
- <p>
- One concern is that <code>bandwidth</code> may be hard to implement,
- can be quite power-consuming to keep up-to-date and its value might be
- unrelated to the actual connection quality that could be affected by
- the server.<br>
- A solution to fix this would be to return non absolute values that
- couldn't be easily abused and would be more simple to produce for the
- <a class="internalDFN" href="#dfn-user-agent">user agent</a>. For example, having a set of values like
- <code>very-slow</code>, <code>slow</code>, <code>fast</code> and
- <code>very-fast</code>. Another solution would be to have only values
- like <code>very-slow</code>, <code>slow</code> and the empty string."
- </p>
- <p>
- <code>metered</code> may also be hard to implement as there is
- currently no standard way for the OS to know if the current connection
- is metered. The approach of the specification is to leave the
- implementation details to the <a class="internalDFN" href="#dfn-user-agent">user agent</a>. That way, the
- attribute could return a value based on a heuristic, on knowledge of
- the current connection status or even by directly asking the user for
- the information.<br>
- It is interesting to point that Android 4.1 and Windows 8 both have a
- way to check if the current connection is metered. Android is using a
- boolean (isActiveNetworkMetered()) while Windows 8 allow the developer
- to ask for different information (NetworkCostType,
- ApproachingDataLimit, OverDataLimit, Roaming).
- <!--
- Android: https://developer.android.com/reference/android/net/ConnectivityManager.html#isActiveNetworkMetered%28%29
- Windows: http://msdn.microsoft.com/en-us/library/windows/apps/hh465399.aspx#adapt
- -->
- </p>
- </section>
- </section>
-
- <section id="conformance"><!--OddPage--><h2><span class="secno">2. </span>Conformance</h2>
-<p>
- As well as sections marked as non-normative, all authoring guidelines, diagrams, examples,
- and notes in this specification are non-normative. Everything else in this specification is
- normative.
-</p>
-<p>
- The key words <em title="must" class="rfc2119">must</em>, <em title="must not" class="rfc2119">must not</em>, <em title="required" class="rfc2119">required</em>, <em title="should" class="rfc2119">should</em>, <em title="should not" class="rfc2119">should not</em>, <em title="recommended" class="rfc2119">recommended</em>, <em title="may" class="rfc2119">may</em>,
- and <em title="optional" class="rfc2119">optional</em> in this specification are to be interpreted as described in [<cite><a href="#bib-RFC2119" class="bibref">RFC2119</a></cite>].
-</p>
-
- <p>
- This specification defines conformance criteria that apply to a single
- product: the <dfn id="dfn-user-agent">user agent</dfn> that implements the interfaces that
- it contains.
- </p>
- <p>
- Implementations that use ECMAScript to expose the APIs defined in this specification must implement them in a manner
- consistent with the ECMAScript Bindings defined in the Web IDL specification [<cite><a href="#bib-WEBIDL" class="bibref">WEBIDL</a></cite>].
- </p>
- </section>
-
- <section id="terminology">
- <!--OddPage--><h2><span class="secno">3. </span>Terminology</h2>
- <p>
- The <code><a href="http://dev.w3.org/html5/spec/webappapis.html#function">
- Function</a></code> interface represents a function in the scripting
- language being used as defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
- </p>
- <p>
- The concepts <dfn id="dfn-queue-a-task"><a href="http://dev.w3.org/html5/spec/webappapis.html#queue-a-task">
- queue a task</a></dfn> and
- <dfn id="dfn-fire-a-simple-event"><a href="http://dev.w3.org/html5/spec/webappapis.html#fire-a-simple-event">
- fire a simple event</a></dfn> are defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
- </p>
-
- <p>
- The terms <dfn id="dfn-event-handlers"> <a href="http://dev.w3.org/html5/spec/webappapis.html#event-handlers">
- event handlers</a></dfn> and
- <dfn id="dfn-event-handler-event-types"><a href="http://dev.w3.org/html5/spec/webappapis.html#event-handler-event-type">
- event handler event types</a></dfn> are defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
- </p>
-
- <p>
- The concepts of <dfn id="dfn-browsing-context"><a href="http://dev.w3.org/html5/spec/browsers.html#browsing-context">
- browsing context</a></dfn> and
- <dfn id="dfn-active-document"><a href="http://dev.w3.org/html5/spec/browsers.html#active-document">
- active document</a></dfn> are defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
- </p>
-
- <p>
- The concept of document <dfn id="dfn-domain"><a href="http://dev.w3.org/html5/spec/origin-0.html#the-document-s-domain">
- domain</a></dfn> is defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
- </p>
- </section>
-
- <section id="security-and-privacy-considerations">
- <!--OddPage--><h2><span class="secno">4. </span>Security and privacy considerations</h2>
- <p>
- The API defined in this specification is used to determine the connection information
- of the hosting device. The information disclosed has minimal
- impact on privacy or fingerprinting, and therefore is exposed without
- permission grants. For example, authors cannot directly know what kind of connection
- is currently in use by the hosting device.
- </p>
- </section>
-
- <section id="the-networkinformation-interface">
- <!--OddPage--><h2><span class="secno">5. </span>The <a class="idlType" href="#idl-def-NetworkInformation"><code>NetworkInformation</code></a> interface</h2>
- <p>
- The <a class="idlType" href="#idl-def-NetworkInformation"><code>NetworkInformation</code></a> interface is exposed on the
- <code>Navigator</code> object.
- </p>
- <pre class="idl"><span class="idlImplements"><a>Navigator</a> implements <a class="idlType" href="#idl-def-NetworkInformation"><code>NetworkInformation</code></a>;</span></pre><div class="idlImplementsDesc"><p>All instances of the <code><a>Navigator</a></code> type are defined to also implement the <a class="idlType" href="#idl-def-NetworkInformation"><code>NetworkInformation</code></a> interface.</p></div>
- <pre class="idl"><span class="idlInterface" id="idl-def-NetworkInformation">[<span class="extAttr">NoInterfaceObject</span>]
-interface <span class="idlInterfaceID">NetworkInformation</span> {
-<span class="idlAttribute"> readonly attribute <span class="idlAttrType"><a class="idlType" href="#idl-def-Connection"><code>Connection</code></a></span> <span class="idlAttrName"><a href="#widl-NetworkInformation-connection">connection</a></span>;</span>
-};</span></pre><section id="attributes"><h3><span class="secno">5.1 </span>Attributes</h3><dl class="attributes"><dt id="widl-NetworkInformation-connection"><code>connection</code> of type <span class="idlAttrType"><a class="idlType" href="#idl-def-Connection"><code>Connection</code></a></span>, readonly</dt><dd>
- The object from which connection information is accessed.
- </dd></dl></section>
- </section>
-
- <section id="the-connection-interface">
- <!--OddPage--><h2><span class="secno">6. </span>The <a class="idlType" href="#idl-def-Connection"><code>Connection</code></a> interface</h2>
- <p>
- The <a class="idlType" href="#idl-def-Connection"><code>Connection</code></a> interface provides a handle to the device's connection information.
- </p>
- <pre class="idl"><span class="idlInterface" id="idl-def-Connection">[<span class="extAttr">NoInterfaceObject</span>]
-interface <span class="idlInterfaceID">Connection</span> : <span class="idlSuperclass"><a>EventTarget</a></span> {
-<span class="idlAttribute"> readonly attribute <span class="idlAttrType"><a>double</a></span> <span class="idlAttrName"><a href="#widl-Connection-bandwidth">bandwidth</a></span>;</span>
-<span class="idlAttribute"> readonly attribute <span class="idlAttrType"><a>boolean</a></span> <span class="idlAttrName"><a href="#widl-Connection-metered">metered</a></span>;</span>
-<span class="idlAttribute"> [<span class="extAttr">TreatNonCallableAsNull</span>]
- attribute <span class="idlAttrType"><a>Function</a>?</span> <span class="idlAttrName"><a href="#widl-Connection-onchange">onchange</a></span>;</span>
-};</span></pre><section id="attributes-1"><h3><span class="secno">6.1 </span>Attributes</h3><dl class="attributes"><dt id="widl-Connection-bandwidth"><code>bandwidth</code> of type <span class="idlAttrType"><a>double</a></span>, readonly</dt><dd>
- The <a class="internalDFN" href="#dfn-user-agent">user agent</a> <em title="must" class="rfc2119">must</em> set the value of the <code>bandwidth</code> attribute to:
- <ul>
- <li>0 if the user is currently offline;</li>
- <li>Infinity if the bandwidth is unknown;</li>
- <li>an estimation of the current bandwidth in MB/s (Megabytes per seconds) available for communication with the
- <a class="internalDFN" href="#dfn-browsing-context">browsing context</a> <a class="internalDFN" href="#dfn-active-document">active document</a>'s <a class="internalDFN" href="#dfn-domain">domain</a>.
- </li>
- </ul>
- </dd><dt id="widl-Connection-metered"><code>metered</code> of type <span class="idlAttrType"><a>boolean</a></span>, readonly</dt><dd>
- <p>
- A connection is <dfn id="dfn-metered">metered</dfn> when the user's connection is subject to a limitation from his Internet Service Provider
- strong enough to request web applications to be careful with the bandwidth usage.
- </p>
- <div class="note"><div class="note-title"><span>Note</span></div><div class="">
- What is a metered connection is voluntarily left to the <a class="internalDFN" href="#dfn-user-agent">user agent</a> to judge. It would not be possible to give an exhaustive
- list of limitations considered strong enough to flag the connection as metered and even if doable, some limitations can be
- considered strong or weak depending on the context.<br>
- Examples of metered connections are mobile connections with a small bandwidth quota or connections with a pay-per use plan.
- </div></div>
- <p>
- The <a class="internalDFN" href="#dfn-user-agent">user agent</a> <em title="must" class="rfc2119">must</em> set the value of the <code>metered</code> attribute to true if the connection with the
- <a class="internalDFN" href="#dfn-browsing-context">browsing context</a> <a class="internalDFN" href="#dfn-active-document">active document</a>'s <a class="internalDFN" href="#dfn-domain">domain</a> is <a class="internalDFN" href="#dfn-metered" title="metered">metered</a> and false otherwise.
- If the implementation is not able to know the status of the connection or if the user is offline, the value <em title="must" class="rfc2119">must</em> be set to false.
- </p>
- <div class="note"><div class="note-title"><span>Note</span></div><div class="">
- If unable to know if a connection is metered, a <a class="internalDFN" href="#dfn-user-agent">user agent</a> could ask the user about the status of his current connection.
- For example, a preference could let the user define if the mobile connection used on the device is metered.
- </div></div>
- </dd><dt id="widl-Connection-onchange"><code>onchange</code> of type <span class="idlAttrType"><a>Function</a></span>, nullable</dt><dd></dd></dl></section>
-
- <p>
- When the <code>Connection</code> changes, the <a class="internalDFN" href="#dfn-user-agent">user agent</a> <em title="must" class="rfc2119">must</em> <a class="internalDFN" href="#dfn-queue-a-task">queue a task</a> which updates
- the <code>Connection</code> properties and <a class="internalDFN" href="#dfn-fire-a-simple-event">fire a simple event</a> named <code>change</code> at the
- <code>Connection</code> object.
- </p>
-
- <p>
- When the user goes online or offline, in addition to the <code>change</code> event fired on the <code>Connection</code>
- object, the <a class="internalDFN" href="#dfn-user-agent">user agent</a> has to <a class="internalDFN" href="#dfn-fire-a-simple-event">fire a simple event</a> named either <code>online</code> or <code>offline</code>
- depending on the applicable value, as defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
- </p>
-
- <section id="event-handlers">
- <h3><span class="secno">6.2 </span>Event handlers</h3>
- <p>
- The following are the <a class="internalDFN" href="#dfn-event-handlers">event handlers</a> (and their corresponding
- <a class="internalDFN" href="#dfn-event-handler-event-types">event handler event types</a>) that <em title="must" class="rfc2119">must</em> be supported as
- attributes by the <code>Connection</code> object:
- </p>
-
- <table class="simple">
- <thead>
- <tr>
- <th>event handler</th>
- <th>event handler event type</th>
- </tr>
- </thead>
- <tbody>
-
- <tr>
- <td><strong><code>onchange</code></strong></td>
- <td><code>change</code></td>
- </tr>
- </tbody>
- </table>
- </section>
- </section>
-
- <section id="examples" class="informative">
- <!--OddPage--><h2><span class="secno">7. </span>Examples</h2><p><em>This section is non-normative.</em></p>
- <p>
- This trivial example writes the connection bandwidth to the console and shows it again each time it is changing:
- </p>
- <div class="example"><div class="example-title"><span>Example 1</span></div><pre class="example highlight prettyprint"><span class="kwd">function</span><span class="pln"> show</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- console</span><span class="pun">.</span><span class="pln">log</span><span class="pun">(</span><span class="pln">navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">bandwidth</span><span class="pun">);</span><span class="pln">
-</span><span class="pun">}</span><span class="pln">
-
-navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">addEventListener</span><span class="pun">(</span><span class="str">'change'</span><span class="pun">,</span><span class="pln"> show</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">false</span><span class="pun">);</span><span class="pln">
-
-show</span><span class="pun">();</span></pre></div>
-
- <p>
- This example shows how an image viewer can select a low definition or a high definition image based on the
- current connection bandwidth:
- </p>
- <div class="example"><div class="example-title"><span>Example 2</span></div><pre class="example highlight prettyprint"><span class="dec"><!DOCTYPE></span><span class="pln">
-</span><span class="tag"><html></span><span class="pln">
- </span><span class="tag"><head></span><span class="pln">
- </span><span class="tag"><title></span><span class="pln">Pony viewer</span><span class="tag"></title></span><span class="pln">
- </span><span class="tag"></head></span><span class="pln">
- </span><span class="tag"><body></span><span class="pln">
- </span><span class="tag"><img</span><span class="pln"> </span><span class="atn">id</span><span class="pun">=</span><span class="atv">'pony'</span><span class="pln"> </span><span class="atn">alt</span><span class="pun">=</span><span class="atv">"An image showing a pony"</span><span class="pln"> </span><span class="atn">title</span><span class="pun">=</span><span class="atv">"My precious!"</span><span class="tag">></span><span class="pln">
- </span><span class="tag"><script></span><span class="pln">
- </span><span class="kwd">var</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> document</span><span class="pun">.</span><span class="pln">getElementById</span><span class="pun">(</span><span class="str">'pony'</span><span class="pun">);</span><span class="pln">
-
- </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="pln">navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">bandwidth </span><span class="pun">></span><span class="pln"> </span><span class="lit">2</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- i</span><span class="pun">.</span><span class="pln">src </span><span class="pun">=</span><span class="pln"> </span><span class="str">"http://example.com/pony_hd.png"</span><span class="pun">;</span><span class="pln">
- </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">else</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- i</span><span class="pun">.</span><span class="pln">src </span><span class="pun">=</span><span class="pln"> </span><span class="str">"http://example.com/pony_ld.png"</span><span class="pun">;</span><span class="pln">
- </span><span class="pun">}</span><span class="pln">
- </span><span class="tag"></script></span><span class="pln">
- </span><span class="tag"></body></span><span class="pln">
-</span><span class="tag"></html></span></pre></div>
-
- <p>
- This example shows how an application can prevent automatic polling using the metered attribute:
- </p>
- <div class="example"><div class="example-title"><span>Example 3</span></div><pre class="example highlight prettyprint"><span class="dec"><!DOCTYPE html></span><span class="pln">
-</span><span class="tag"><html></span><span class="pln">
- </span><span class="tag"><head></span><span class="pln">
- </span><span class="tag"><title></span><span class="pln">Conditional polling</span><span class="tag"></title></span><span class="pln">
- </span><span class="tag"><script></span><span class="pln">
- </span><span class="kwd">var</span><span class="pln"> gPreviousMetered </span><span class="pun">=</span><span class="pln"> navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">;</span><span class="pln">
- </span><span class="kwd">var</span><span class="pln"> gIntervalId</span><span class="pun">;</span><span class="pln">
-
- </span><span class="kwd">function</span><span class="pln"> poll</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- </span><span class="com">// poll stuff</span><span class="pln">
- </span><span class="pun">}</span><span class="pln">
-
- navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">addEventListener</span><span class="pun">(</span><span class="str">'change'</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">function</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="pln">gPreviousMetered </span><span class="pun">==</span><span class="pln"> navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- </span><span class="kwd">return</span><span class="pun">;</span><span class="pln">
- </span><span class="pun">}</span><span class="pln">
-
- gPreviousMetered </span><span class="pun">=</span><span class="pln"> navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">;</span><span class="pln">
- </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(!</span><span class="pln">navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- gIntervalId </span><span class="pun">=</span><span class="pln"> setInterval</span><span class="pun">(</span><span class="pln">poll</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1000</span><span class="pun">);</span><span class="pln">
- </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">else</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- clearInterval</span><span class="pun">(</span><span class="pln">gIntervalId</span><span class="pun">);</span><span class="pln">
- </span><span class="pun">}</span><span class="pln">
- </span><span class="pun">},</span><span class="pln"> </span><span class="kwd">false</span><span class="pun">);</span><span class="pln">
-
- </span><span class="com">// At load time.</span><span class="pln">
- </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(!</span><span class="pln">navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
- gIntervalId </span><span class="pun">=</span><span class="pln"> setInterval</span><span class="pun">(</span><span class="pln">poll</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1000</span><span class="pun">);</span><span class="pln">
- </span><span class="pun">}</span><span class="pln">
- </span><span class="tag"></script></span><span class="pln">
- </span><span class="tag"></head></span><span class="pln">
- </span><span class="tag"><body></span><span class="pln">
- </span><span class="tag"><button</span><span class="pln"> </span><span class="atn">onclick</span><span class="pun">=</span><span class="atv">"</span><span class="pln">poll</span><span class="pun">();</span><span class="atv">"</span><span class="tag">></span><span class="pln">Poll</span><span class="tag"></button></span><span class="pln">
- </span><span class="tag"></body></span><span class="pln">
-</span><span class="tag"></html></span></pre></div>
- </section>
-
- <section id="acknowledgments" class="appendix">
- <!--OddPage--><h2><span class="secno">A. </span>Acknowledgments</h2>
- <p>
- Thanks to Robin Berjon, Frederick Hirsch and Jonas Sicking for their help.
- </p>
- </section>
-
-<section class="appendix" id="references"><!--OddPage--><h2><span class="secno">B. </span>References</h2><section id="normative-references"><h3><span class="secno">B.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-HTML5">[HTML5]</dt><dd>Ian Hickson; David Hyatt. <a href="http://www.w3.org/TR/html5"><cite>HTML5.</cite></a> 29 March 2012. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/html5">http://www.w3.org/TR/html5</a>
-</dd><dt id="bib-RFC2119">[RFC2119]</dt><dd>S. Bradner. <a href="http://www.ietf.org/rfc/rfc2119.txt"><cite>Key words for use in RFCs to Indicate Requirement Levels.</cite></a> March 1997. Internet RFC 2119. URL: <a href="http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a>
-</dd><dt id="bib-WEBIDL">[WEBIDL]</dt><dd>Cameron McCormack. <a href="http://www.w3.org/TR/2011/WD-WebIDL-20110927/"><cite>Web IDL.</cite></a> 27 September 2011. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2011/WD-WebIDL-20110927/">http://www.w3.org/TR/2011/WD-WebIDL-20110927/</a>
-</dd></dl></section></section></body></html>
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