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<!DOCTYPE html><!-- This page is a placeholder for generated extensions api doc. Note:
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Description of this parameter from the json schema.
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<h1 class="page_title">Background Pages</h1>
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<!-- 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>"background_page": "background.html"
</pre>
<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 class="apiGroup" id="methods">
<a name="methods"></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>
</div> <!-- /description -->
</div> <!-- /apiItem -->
</div> <!-- /apiGroup -->
<!-- EVENTS -->
<div class="apiGroup">
<a name="events"></a>
<h3 id="events">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 -->
<h4>Parameters</h4>
<dl>
<div>
<div>
</div>
</div>
</dl>
</div> <!-- /decription -->
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<a name="types.sort(sortByName)"></a>
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<!-- iterates over all types -->
<div class="apiItem">
<a></a>
<h4>type name</h4>
<div>
</div>
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