<!DOCTYPE html><!-- This page is a placeholder for generated extensions api doc. Note:
1) The <head> information in this page is significant, should be uniform
across api docs and should be edited only with knowledge of the
templating mechanism.
3) All <body>.innerHTML is genereated as an rendering step. If viewed in a
browser, it will be re-generated from the template, json schema and
authored overview content.
4) The <body>.innerHTML is also generated by an offline step so that this
page may easily be indexed by search engines.
--><html xmlns="http://www.w3.org/1999/xhtml"><head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<link href="css/ApiRefStyles.css" rel="stylesheet" type="text/css">
<link href="css/print.css" rel="stylesheet" type="text/css" media="print">
<script type="text/javascript" src="../../../third_party/jstemplate/jstemplate_compiled.js">
</script>
<script type="text/javascript" src="js/api_page_generator.js"></script>
<script type="text/javascript" src="js/bootstrap.js"></script>
<script type="text/javascript" src="js/sidebar.js"></script>
<title>Background Pages - Google Chrome Extensions - Google Code</title></head>
<body> <div id="gc-container" class="labs">
<div id="devModeWarning">
You are viewing extension docs in chrome via the 'file:' scheme: are you expecting to see local changes when you refresh? You'll need run chrome with --allow-file-access-from-files.
</div>
<!-- SUBTEMPLATES: DO NOT MOVE FROM THIS LOCATION -->
<!-- In particular, sub-templates that recurse, must be used by allowing
jstemplate to make a copy of the template in this section which
are not operated on by way of the jsskip="true" -->
<div style="display:none">
<!-- VALUE -->
<div id="valueTemplate">
<dt>
<var>paramName</var>
<em>
<!-- TYPE -->
<div style="display:inline">
(
<span class="optional">optional</span>
<span class="enum">enumerated</span>
<span id="typeTemplate">
<span>
<a> Type</a>
</span>
<span>
<span>
array of <span><span></span></span>
</span>
<span>paramType</span>
<span></span>
</span>
</span>
)
</div>
</em>
</dt>
<dd class="todo">
Undocumented.
</dd>
<dd>
Description of this parameter from the json schema.
</dd>
<dd>
This parameter was added in version
<b><span></span></b>.
You must omit this parameter in earlier versions,
and you may omit it in any version. If you require this
parameter, the manifest key
<a href="manifest.html#minimum_chrome_version">minimum_chrome_version</a>
can ensure that your extension won't be run in an earlier browser version.
</dd>
<!-- OBJECT PROPERTIES -->
<dd>
<dl>
<div>
<div>
</div>
</div>
</dl>
</dd>
<!-- OBJECT METHODS -->
<dd>
<div></div>
</dd>
<!-- OBJECT EVENT FIELDS -->
<dd>
<div></div>
</dd>
<!-- FUNCTION PARAMETERS -->
<dd>
<div></div>
</dd>
</div> <!-- /VALUE -->
<div id="functionParametersTemplate">
<h5>Parameters</h5>
<dl>
<div>
<div>
</div>
</div>
</dl>
</div>
</div> <!-- /SUBTEMPLATES -->
<a id="top"></a>
<div id="skipto">
<a href="#gc-pagecontent">Skip to page content</a>
<a href="#gc-toc">Skip to main navigation</a>
</div>
<!-- API HEADER -->
<table id="header" width="100%" cellspacing="0" border="0">
<tbody><tr>
<td valign="middle"><a href="http://code.google.com/"><img src="images/code_labs_logo.gif" height="43" width="161" alt="Google Code Labs" style="border:0; margin:0;"></a></td>
<td valign="middle" width="100%" style="padding-left:0.6em;">
<form action="http://www.google.com/cse" id="cse" style="margin-top:0.5em">
<div id="gsc-search-box">
<input type="hidden" name="cx" value="002967670403910741006:61_cvzfqtno">
<input type="hidden" name="ie" value="UTF-8">
<input type="text" name="q" value="" size="55">
<input class="gsc-search-button" type="submit" name="sa" value="Search">
<br>
<span class="greytext">e.g. "page action" or "tabs"</span>
</div>
</form>
<script type="text/javascript" src="http://www.google.com/jsapi"></script>
<script type="text/javascript">google.load("elements", "1", {packages: "transliteration"});</script>
<script type="text/javascript" src="http://www.google.com/coop/cse/t13n?form=cse&t13n_langs=en"></script>
<script type="text/javascript" src="http://www.google.com/coop/cse/brand?form=cse&lang=en"></script>
</td>
</tr>
</tbody></table>
<div id="codesiteContent" class="">
<a id="gc-topnav-anchor"></a>
<div id="gc-topnav">
<h1>Google Chrome Extensions (<a href="http://code.google.com/labs/">Labs</a>)</h1>
<ul id="home" class="gc-topnav-tabs">
<li id="home_link">
<a href="index.html" title="Google Chrome Extensions home page">Home</a>
</li>
<li id="docs_link">
<a href="docs.html" title="Official Google Chrome Extensions documentation">Docs</a>
</li>
<li id="faq_link">
<a href="faq.html" title="Answers to frequently asked questions about Google Chrome Extensions">FAQ</a>
</li>
<li id="samples_link">
<a href="samples.html" title="Sample extensions (with source code)">Samples</a>
</li>
<li id="group_link">
<a href="http://groups.google.com/a/chromium.org/group/chromium-extensions" title="Google Chrome Extensions developer forum">Group</a>
</li>
</ul>
</div> <!-- end gc-topnav -->
<div class="g-section g-tpl-170">
<!-- SIDENAV -->
<div class="g-unit g-first" id="gc-toc">
<ul>
<li><a href="getstarted.html">Getting Started</a></li>
<li><a href="overview.html">Overview</a></li>
<li><a href="whats_new.html">What's New?</a></li>
<li><h2><a href="devguide.html">Developer's Guide</a></h2>
<ul>
<li>Browser UI
<ul>
<li><a href="browserAction.html">Browser Actions</a></li>
<li><a href="contextMenus.html">Context Menus</a></li>
<li><a href="notifications.html">Desktop Notifications</a></li>
<li><a href="omnibox.html">Omnibox</a></li>
<li><a href="options.html">Options Pages</a></li>
<li><a href="override.html">Override Pages</a></li>
<li><a href="pageAction.html">Page Actions</a></li>
</ul>
</li>
<li>Browser Interaction
<ul>
<li><a href="bookmarks.html">Bookmarks</a></li>
<li><a href="cookies.html">Cookies</a></li>
<li><a href="events.html">Events</a></li>
<li><a href="history.html">History</a></li>
<li><a href="management.html">Management</a></li>
<li><a href="tabs.html">Tabs</a></li>
<li><a href="windows.html">Windows</a></li>
</ul>
</li>
<li>Implementation
<ul>
<li><a href="a11y.html">Accessibility</a></li>
<li class="leftNavSelected">Background Pages</li>
<li><a href="content_scripts.html">Content Scripts</a></li>
<li><a href="xhr.html">Cross-Origin XHR</a></li>
<li><a href="idle.html">Idle</a></li>
<li><a href="i18n.html">Internationalization</a></li>
<li><a href="messaging.html">Message Passing</a></li>
<li><a href="npapi.html">NPAPI Plugins</a></li>
</ul>
</li>
<li>Finishing
<ul>
<li><a href="hosting.html">Hosting</a></li>
<li><a href="external_extensions.html">Other Deployment Options</a></li>
</ul>
</li>
</ul>
</li>
<li><h2><a href="apps.html">Packaged Apps</a></h2></li>
<li><h2><a href="tutorials.html">Tutorials</a></h2>
<ul>
<li><a href="tut_debugging.html">Debugging</a></li>
<li><a href="tut_analytics.html">Google Analytics</a></li>
<li><a href="tut_oauth.html">OAuth</a></li>
</ul>
</li>
<li><h2>Reference</h2>
<ul>
<li>Formats
<ul>
<li><a href="manifest.html">Manifest Files</a></li>
<li><a href="match_patterns.html">Match Patterns</a></li>
</ul>
</li>
<li><a href="permission_warnings.html">Permission Warnings</a></li>
<li><a href="api_index.html">chrome.* APIs</a></li>
<li><a href="api_other.html">Other APIs</a></li>
</ul>
</li>
<li><h2><a href="samples.html">Samples</a></h2></li>
<div class="line"> </div>
<li><h2>More</h2>
<ul>
<li><a href="http://code.google.com/chrome/webstore/docs/index.html">Chrome Web Store</a></li>
<li><a href="http://code.google.com/chrome/apps/docs/developers_guide.html">Hosted Apps</a></li>
<li><a href="themes.html">Themes</a></li>
</ul>
</li>
</ul>
</div>
<script>
initToggles();
</script>
<div class="g-unit" id="gc-pagecontent">
<div id="pageTitle">
<h1 class="page_title">Background Pages</h1>
</div>
<!-- TABLE OF CONTENTS -->
<div id="toc">
<h2>Contents</h2>
<ol>
<li>
<a href="#manifest">Manifest</a>
<ol>
<li style="display: none; ">
<a>h3Name</a>
</li>
</ol>
</li><li>
<a href="#H2-1">Details</a>
<ol>
<li style="display: none; ">
<a>h3Name</a>
</li>
</ol>
</li><li>
<a href="#example">Example</a>
<ol>
<li style="display: none; ">
<a>h3Name</a>
</li>
</ol>
</li>
<li style="display: none; ">
<a href="#apiReference">API reference</a>
<ol>
<li>
<a href="#properties">Properties</a>
<ol>
<li>
<a href="#property-anchor">propertyName</a>
</li>
</ol>
</li>
<li>
<a>Methods</a>
<ol>
<li>
<a href="#method-anchor">methodName</a>
</li>
</ol>
</li>
<li>
<a>Events</a>
<ol>
<li>
<a href="#event-anchor">eventName</a>
</li>
</ol>
</li>
<li>
<a href="#types">Types</a>
<ol>
<li>
<a href="#id-anchor">id</a>
</li>
</ol>
</li>
</ol>
</li>
</ol>
</div>
<!-- /TABLE OF CONTENTS -->
<!-- Standard content lead-in for experimental API pages -->
<p id="classSummary" style="display: none; ">
For information on how to use experimental APIs, see the <a href="experimental.html">chrome.experimental.* APIs</a> page.
</p>
<!-- STATIC CONTENT PLACEHOLDER -->
<div id="static"><div id="pageData-name" class="pageData">Background Pages</div>
<div id="pageData-showTOC" class="pageData">true</div>
<p>
A common need for extensions is to have
a single long-running script to manage some task or state.
Background pages to the rescue.
</p>
<p>
As the <a href="overview.html#arch">architecture overview</a> explains,
the background page is an HTML page that runs in the extension process.
It exists for the lifetime of your extension,
and only one instance of it at a time is active.
</p>
<p>
In a typical extension with a background page,
the UI —
for example, the browser action or page action
and any options page —
is implemented by dumb views.
When the view needs some state,
it requests the state from the background page.
When the background page notices a state change,
the background page tells the views to update.
</p>
<h2 id="manifest">Manifest</h2>
<p>
Register your background page in the
<a href="manifest.html">extension manifest</a>
like this:
</p>
<pre>{
"name": "My extension",
...
<b>"background_page": "background.html"</b>,
...
}</pre>
<p>
If you need the browser to start up early—so
you can display notifications, for example—then
you might also want to specify the
<a href="manifest.html#permissions">"background" permission</a>.
</p>
<a name="H2-1"></a><h2>Details</h2>
<p>
You can communicate between your various pages using direct script calls,
similar to how frames can communicate.
The <a href="extension.html#method-getViews"><code>chrome.extension.getViews()</code></a> method
returns a list of window objects
for every active page belonging to your extension,
and the
<a href="extension.html#method-getBackgroundPage"><code>chrome.extension.getBackgroundPage()</code></a> method
returns the background page.
</p>
<h2 id="example">Example</h2>
<p>
The following code snippet demonstrates
how the background page
can interact with other pages in the extension.
It also shows how you can use
the background page to handle events
such as user clicks.
</p>
<p>
The extension in this example
has a background page
and multiple pages created
(with
<a href="tabs.html#method-create"><code>chrome.tabs.create()</code></a>)
from a file named <code>image.html</code>.
<!-- [PENDING: Once we have our set of samples, we should point to the example this is from and to other relevant examples. This is currently untested code derived from the screenshot sample.] -->
</p>
<pre><em>//In the background page:</em>
<html>
<script>
//React when a browser action's icon is clicked.
chrome.browserAction.onClicked.addListener(function(tab) {
var viewTabUrl = chrome.extension.getURL('image.html');
var imageUrl = <em>/* an image's URL */</em>;
//Look through all the pages in this extension to find one we can use.
var views = chrome.extension.getViews();
for (var i = 0; i < views.length; i++) {
var view = views[i];
//If this view has the right URL and hasn't been used yet...
if (view.location.href == viewTabUrl && !view.imageAlreadySet) {
//...call one of its functions and set a property.
view.setImageUrl(imageUrl);
view.imageAlreadySet = true;
break; //we're done
}
}
});
</script>
</html>
<em>//In image.html:</em>
<html>
<script>
function setImageUrl(url) {
document.getElementById('target').src = url;
}
</script>
<body>
<p>
Image here:
</p>
<img id="target" src="white.png" width="640" height="480">
</body>
</html>
</pre>
</div>
<!-- API PAGE -->
<div class="apiPage" style="display: none; ">
<a name="apiReference"></a>
<h2>API reference: chrome.apiname </h2>
<!-- PROPERTIES -->
<div class="apiGroup">
<a name="properties"></a>
<h3 id="properties">Properties</h3>
<div>
<a></a>
<h4>getLastError</h4>
<div class="summary">
<!-- Note: intentionally longer 80 columns -->
<span>chrome.extension</span><span>lastError</span>
</div>
<div>
</div>
</div>
</div> <!-- /apiGroup -->
<!-- METHODS -->
<div id="methodsTemplate" class="apiGroup">
<a></a>
<h3>Methods</h3>
<!-- iterates over all functions -->
<div class="apiItem">
<a></a> <!-- method-anchor -->
<h4>method name</h4>
<div class="summary"><span>void</span>
<!-- Note: intentionally longer 80 columns -->
<span>chrome.module.methodName</span>(<span><span>, </span><span></span>
<var><span></span></var></span>)</div>
<div class="description">
<p class="todo">Undocumented.</p>
<p>
A description from the json schema def of the function goes here.
</p>
<!-- PARAMETERS -->
<h4>Parameters</h4>
<dl>
<div>
<div>
</div>
</div>
</dl>
<!-- RETURNS -->
<h4>Returns</h4>
<dl>
<div>
<div>
</div>
</div>
</dl>
<!-- CALLBACK -->
<div>
<div>
<h4>Callback function</h4>
<p>
The callback <em>parameter</em> should specify a function
that looks like this:
</p>
<p>
If you specify the <em>callback</em> parameter, it should
specify a function that looks like this:
</p>
<!-- Note: intentionally longer 80 columns -->
<pre>function(<span>Type param1, Type param2</span>) <span class="subdued">{...}</span>;</pre>
<dl>
<div>
<div>
</div>
</div>
</dl>
</div>
</div>
<!-- MIN_VERSION -->
<p>
This function was added in version <b><span></span></b>.
If you require this function, the manifest key
<a href="manifest.html#minimum_chrome_version">minimum_chrome_version</a>
can ensure that your extension won't be run in an earlier browser version.
</p>
</div> <!-- /description -->
</div> <!-- /apiItem -->
</div> <!-- /apiGroup -->
<!-- EVENTS -->
<div id="eventsTemplate" class="apiGroup">
<a></a>
<h3>Events</h3>
<!-- iterates over all events -->
<div class="apiItem">
<a></a>
<h4>event name</h4>
<div class="summary">
<!-- Note: intentionally longer 80 columns -->
<span class="subdued">chrome.bookmarks</span><span>onEvent</span><span class="subdued">.addListener</span>(function(<span>Type param1, Type param2</span>) <span class="subdued">{...}</span>);
</div>
<div class="description">
<p class="todo">Undocumented.</p>
<p>
A description from the json schema def of the event goes here.
</p>
<!-- PARAMETERS -->
<div>
<h4>Parameters</h4>
<dl>
<div>
<div>
</div>
</div>
</dl>
</div>
</div> <!-- /decription -->
</div> <!-- /apiItem -->
</div> <!-- /apiGroup -->
<!-- TYPES -->
<div class="apiGroup">
<a name="types"></a>
<h3 id="types">Types</h3>
<!-- iterates over all types -->
<div class="apiItem">
<a></a>
<h4>type name</h4>
<div>
</div>
</div> <!-- /apiItem -->
</div> <!-- /apiGroup -->
</div> <!-- /apiPage -->
</div> <!-- /gc-pagecontent -->
</div> <!-- /g-section -->
</div> <!-- /codesiteContent -->
<div id="gc-footer" --="">
<div class="text">
<p>
Except as otherwise <a href="http://code.google.com/policies.html#restrictions">noted</a>,
the content of this page is licensed under the <a rel="license" href="http://creativecommons.org/licenses/by/3.0/">Creative Commons
Attribution 3.0 License</a>, and code samples are licensed under the
<a rel="license" href="http://code.google.com/google_bsd_license.html">BSD License</a>.
</p>
<p>
©2011 Google
</p>
<!-- begin analytics -->
<script src="http://www.google-analytics.com/urchin.js" type="text/javascript"></script>
<script src="http://www.google-analytics.com/ga.js" type="text/javascript"></script>
<script type="text/javascript">
// chrome doc tracking
try {
var engdocs = _gat._getTracker("YT-10763712-2");
engdocs._trackPageview();
} catch(err) {}
// code.google.com site-wide tracking
try {
_uacct="UA-18071-1";
_uanchor=1;
_uff=0;
urchinTracker();
}
catch(e) {/* urchinTracker not available. */}
</script>
<!-- end analytics -->
</div>
</div> <!-- /gc-footer -->
</div> <!-- /gc-container -->
</body></html>