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<h1 class="page_title">Frequently Asked Questions</h1>
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<div id="static"><div id="pageData-name" class="pageData">Frequently Asked Questions</div>
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<p>
If you don't find an answer to your question here,
try the
<a href="http://code.google.com/chrome/webstore/faq.html">Chrome Web Store FAQ</a>, the
<a href="http://groups.google.com/a/chromium.org/group/chromium-extensions">group</a>, or the
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<div id="faq-TOC">
<h4>General</h4>
<ul>
<li><a href="#faq-gen-01">What are Google Chrome Extensions?</a></li>
<li><a href="#faq-dev-01">How can I set up Chrome for extension development?</a></li>
<li><a href="#faq-gen-02">What technologies are used to write extensions for Chrome?</a></li>
<li><a href="#faq-gen-03">Are extensions fetched from the web every time the browser is loaded?</a></li>
<li><a href="#faq-dev-14">How do I determine which version of Chrome is deployed to which channel?</a></li>
</ul>
<h4>Capabilities</h4>
<ul>
<li><a href="#faq-dev-02">Can extensions make cross-domain Ajax requests?</a></li>
<li><a href="#faq-dev-03">Can extensions use 3rd party web services?</a></li>
<li><a href="#faq-dev-07">Can extensions encode/decode JSON data?</a></li>
<li><a href="#faq-dev-08">Can extensions store data locally?</a></li>
<li><a href="#faq-dev-04">Can extensions use OAuth?</a></li>
<li><a href="#faq-dev-06">Can extensions load DLLs?</a></li>
<li><a href="#faq-dev-05">Can extensions create UI outside of the rendered web page?</a></li>
<li><a href="#faq-interact-chrome">Can extensions listen to clicks on Chrome tabs and navigation buttons?</a>
</li><li><a href="#faq-dev-11">Can two extensions communicate with each other?</a></li>
<li><a href="#faq-dev-13">Can extensions use Google Analytics?</a></li>
<li><a href="#faq-dev-15">Can extensions modify chrome:// URLs?</a></li>
<li><a href="#faq-open-popups">Can extensions open browser/page action popups without user interaction?</a></li>
<li><a href="#faq-persist-popups">Can extensions keep popups open after the user clicks away from them?</a></li>
<li><a href="#faq-lifecycle-events">Can extensions be notified when they are installed/uninstalled?</a></li>
</ul>
<h4>Development</h4>
<ul>
<li><a href="#faq-building-ui">How do I build a UI for my extension?</a>
</li><li><a href="#faq-dev-09">How much data can I store in localStorage?</a></li>
<li><a href="#faq-dev-10">How do I create an options menu for my application?</a></li>
<li><a href="#faq-dev-12">What debugging tools are available to extension developers?</a></li>
<li><a href="#faq-dev-16">Why do wildcard matches not work for top level domains (TLDs)?</a></li>
<li><a href="#faq-management">Why does the management API not fire events when my extension is installed/uninstalled?</a></li>
<li><a href="#faq-firstrun">How can an extension determine whether it is running for the first time?</a></li>
</ul>
<h4>Features and bugs</h4>
<ul>
<li><a href="#faq-fea-01">I think I've found a bug! How do I make sure it gets fixed?</a></li>
<li><a href="#faq-fea-02">I have a feature request! How can I report it?</a></li>
</ul>
</div>
<h2>General</h2>
<h3 id="faq-gen-01">What are Google Chrome Extensions?</h3>
<p>
Google Chrome Extensions are applications that run inside the
Chrome browser and provide additional functionality, integration with third
party websites or services, and customized browsing experiences.
</p>
<h3 id="faq-dev-01">How can I set up Chrome for extension development?</h3>
<p>
As long as you are using a version of Chrome that supports
extensions, you already have everything you need to start writing an
extension of your own.
You can start by turning on Developer mode.
</p>
<p>
Click the wrench icon
<img src="images/toolsmenu.gif" height="29" width="29" alt="" class="nomargin">
and select <b>Extensions</b> from the <b>Tools</b> menu.
If there's a "+" next to "Developer mode",
click the "+" so it turns into a "-".
Now you can reload extensions,
load an unpacked directory of files as if it were a packaged extension,
and more. For a complete tutorial, see
<a href="http://code.google.com/chrome/extensions/getstarted.html">Getting Started</a>.
</p>
<h3 id="faq-gen-02">What technologies are used to write extensions for Chrome?</h3>
<p>
Extensions are written using the same standard web
technologies that developers use to create websites. HTML is used as a
content markup language, CSS is used for styling, and JavaScript for
scripting. Because Chrome supports HTML5 and CSS3, developers can
use the latest open web technologies such as canvas and CSS animations in
their extensions. Extensions also have access to several
<a href="http://code.google.com/chrome/extensions/api_other.html">JavaScript APIs</a>
that help perform functions like JSON encoding and interacting with the
browser.
</p>
<h3 id="faq-gen-03">Are extensions fetched from the web every time the browser is loaded?</h3>
<p>
Extensions are downloaded by the Chrome browser upon install, and
are subsequently run off of the local disk in order to speed up
performance. However, if a new version of the extension is pushed online,
it will be automatically downloaded in the background to any users who
have the extension installed. Extensions may also make requests for remote
content at any time, in order to interact with a web service or pull new
content from the web.
</p>
<h3 id="faq-dev-14">How do I determine which version of Chrome is deployed to which channel?</h3>
<p>
To determine which version of Chrome is currently available on each
of the different platforms, visit
<a href="http://omahaproxy.appspot.com">omahaproxy.appspot.com</a>. On that
site you will see data in a format similar to:
</p>
<pre>cf,dev,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
cf,beta,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
cf,stable,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
linux,dev,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
linux,beta,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
linux,stable,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
mac,dev,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
mac,beta,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
mac,stable,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
win,canary,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
win,dev,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
win,beta,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
win,stable,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
cros,dev,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####
cros,beta,#.#.###.#,#.#.###.#,mm/dd/yy,mm/dd/yy,#####,#####,#####</pre>
<p>
Each line represents information about a different platform and channel
combination. The
listed platforms are <code>cf</code> (Google Chrome Frame),
<code>linux</code>, <code>mac</code>, <code>win</code>, and
<code>cros</code> (Google Chrome OS). The listed
channels are <code>canary</code>, <code>dev</code>, <code>beta</code>,
and <code>stable</code>.
The two four-part numbers after the channel represent the current and previous
versions of Chrome deployed to that platform-channel
combination. The rest of the information is metadata about when the releases
were first pushed, as well as revision numbers associated with each build.
</p>
<h2>Capabilities</h2>
<h3 id="faq-dev-02">Can extensions make cross-domain Ajax requests?</h3>
<p>
Yes. Extensions can make cross-domain requests. See
<a href="http://code.google.com/chrome/extensions/xhr.html">this page</a>
for more information.
</p>
<h3 id="faq-dev-03">Can extensions use 3rd party web services?</h3>
<p>
Yes. Extensions are capable of making cross-domain Ajax
requests, so they can call remote APIs directly. APIs that provide data
in JSON format are particularly easy to use.
</p>
<h3 id="faq-dev-07">Can extensions encode/decode JSON data?</h3>
<p>
Yes, because V8 (Chrome's JavaScript engine) supports
JSON.stringify and JSON.parse natively, you may use these functions in your
extensions
<a href="http://json.org/js.html">as described here</a> without including
any additional JSON libraries in your code.
</p>
<h3 id="faq-dev-08">Can extensions store data locally?</h3>
<p>
Yes, extensions can use <a href="http://dev.w3.org/html5/webstorage/">localStorage</a>
to store string data permanently. Using Chrome's built-in JSON
functions, you can store complex data structures in localStorage. For
extensions that need to execute SQL queries on their stored data,
Chrome implements
<a href="http://dev.w3.org/html5/webdatabase/">client side SQL databases</a>,
which may be used as well.
</p>
<h3 id="faq-dev-04">Can extensions use OAuth?</h3>
<p>
Yes, there are extensions that use OAuth to access remote data
APIs. Most developers find it convenient to use a
<a href="http://unitedheroes.net/OAuthSimple/js/OAuthSimple.js">JavaScript OAuth library</a>
in order to simplify the process of signing OAuth requests.
</p>
<h3 id="faq-dev-06">Can extensions load DLLs?</h3>
<p>
Yes, using the <a href="npapi.html">NPAPI interface</a>.
Because of the possibility for abuse, though, we will review your extension
before hosting it in the Google Chrome Extensions Gallery
or Chrome Web Store.
</p>
<h3 id="faq-dev-05">Can extensions create UI outside of the rendered web page?</h3>
<p>
Yes, your extension may add buttons to the Chrome browser's user interface.
See <a href="browserAction.html">browser actions</a> and
<a href="pageAction.html">page actions</a> for more information.
</p>
<p>
An extension may also create popup notifications, which exist outside of the
browser window. See the <a href="notifications.html">desktop
notifications</a> documentation for more details.
</p>
<h3 id="faq-interact-chrome">Can extensions listen to clicks on Chrome tabs and
navigation buttons?</h3>
<p>
No. Extensions are limited to listening to the events described in the <a href="api_index.html">API documentation</a>.
</p>
<h3 id="faq-dev-11">Can two extensions communicate with each other?</h3>
<p>
Yes, extensions may pass messages to other extensions. See the
<a href="messaging.html#external">message passing documentation</a>
for more information.
</p>
<h3 id="faq-dev-13">Can extensions use Google Analytics?</h3>
<p>
Yes, since extensions are built just like websites, they can use
<a href="http://www.google.com/analytics/">Google Analytics</a> to track
usage. However, we strongly advise you to modify the tracking code to pull
an HTTPS version of the Google Analytics library. See
<a href="tut_analytics.html">this tutorial</a> for more information on doing
this.
</p>
<h3 id="faq-dev-15">Can extensions modify chrome:// URLs?</h3>
<p>
No. The extensions APIs have been designed to minimize backwards
compatibility issues that can arise when new versions of the browser are
pushed. Allowing content scripts on <code>chrome://</code>
URLs would mean that developers would begin to rely on the DOM, CSS, and
JavaScript of these pages to stay the same. In the best case, these pages
could not be updated as quickly as they are being updated right now.
In the worst case, it could mean that an update to one
of these pages could cause an extension to break, causing key parts of the
browser to stop working for users of that extension.
</p>
<p>
The reason that <a href="override.html">replacing the content</a>
hosted at these URLs entirely is
allowed is because it forces an extension developer to implement all of the
functionality they want without depending on the browser's internal implementation
to stay the same.
</p>
<h3 id="faq-open-popups">Can extensions open browser/page action popups without
user interaction?</h3>
<p>
No, popups can only be opened if the user clicks on the corresponding page or
browser action. An extension cannot open its popup programatically.
</p>
<h3 id="faq-persist-popups">Can extensions keep popups open after the user
clicks away from them?</h3>
<p>
No, popups automatically close when the user focuses on some portion of the
browser outside of the popup. There is no way to keep the popup open after
the user has clicked away.
</p>
<h3 id="faq-lifecycle-events">Can extensions be notified when they are
installed/uninstalled?</h3>
<p>
No, there are no events an extension can listen to in order to determine
whether it has been installed or uninstalled. However, an extension can
determine when it has been run for the first time. See <a href="#faq-firstrun">this FAQ entry</a> for information.
</p>
<h2>Development</h2>
<h3 id="faq-building-ui">How do I build a UI for my extension?</h3>
<p>
Extensions use HTML and CSS to define their user interfaces, so you can use
standard form controls to build your UI, or style the interface with CSS,
as you would a web page. Additionally, extensions can add
<a href="#faq-dev-05">some limited UI elements to Chrome itself.</a>
</p>
<h3 id="faq-dev-09">How much data can I store in localStorage?</h3>
<p>
Extensions can store up to 5MB of data in localStorage.
</p>
<h3 id="faq-dev-10">How do I create an options menu for my application?</h3>
<p>
You can let users set options for your extension by creating an
<a href="http://code.google.com/chrome/extensions/trunk/options.html">options page</a>,
which is a simple HTML page that will be loaded when a user clicks the
"options" button for your extension. This page can read and write settings
to localStorage, or even send options to a web server so that they can be
persisted across browsers.
</p>
<h3 id="faq-dev-12">What debugging tools are available to extension developers?</h3>
<p>
Chrome's built-in developer tools can be used to debug extensions
as well as web pages. See this
<a href="http://code.google.com/chrome/extensions/tut_debugging.html ">tutorial on debugging extensions</a>
for more information.
</p>
<h3 id="faq-dev-16">Why do wildcard matches not work for top level domains
(TLDs)?</h3>
<p>
You cannot use wildcard match patterns like <code>http://google.*/*</code>
to match TLDs (like <code>http://google.es</code> and
<code>http://google.fr</code>) due to the
complexity of actually restricting such a match to only the desired domains.
</p>
<p>
For the example of <code>http://google.*/*</code>, the Google domains would
be matched, but so would <code>http://google.someotherdomain.com</code>.
Additionally, many sites do not own all of the TLDs for their
domain. For an example, assume you want to use
<code>http://example.*/*</code> to match <code>http://example.com</code> and
<code>http://example.es</code>, but <code>http://example.net</code> is a
hostile site. If your extension has a bug, the hostile site could potentially
attack your extension in order to get access to your extension's increased
privileges.
</p>
<p>
You should explicitly enumerate the TLDs that you wish to run
your extension on.
</p>
<h3 id="faq-management">Why does the management API not fire events when my
extension is installed/uninstalled?</h3>
<p>
The <a href="management.html">management API</a> was intended to help create
new tab page replacement extensions. It was not intended to fire
install/uninstall events for the current extension.
</p>
<h3 id="faq-firstrun">How can an extension determine whether it is running for
the first time?</h3>
<p>
An extension can check to see whether it is running for the first time by
checking for the presence of a value in localStorage, and writing the value if
it does not exist. For example:
</p>
<pre>var firstRun = (localStorage['firstRun'] == 'true');
if (!firstRun) {
localStorage['firstRun'] = 'true';
}</pre>
<p>
Note that this check should be run in a background page, not a content script.
</p>
<h2>Features and bugs</h2>
<h3 id="faq-fea-01">I think I've found a bug! How do I make sure it gets
fixed?</h3>
<p>
While developing an extension, you may find behavior that does not
match the extensions documentation and may be the result of a bug in
Chrome. The best thing to do is to make sure an appropriate issue
report is filed, and the Chromium team has enough information to reproduce
the behavior.
</p>
<p>The steps you should follow to ensure this are:</p>
<ol>
<li>
Come up with a <em>minimal</em> test extension that demonstrates the issue
you wish to report. This extension should have as little code as possible
to demonstrate the bug—generally this should be 100 lines of
code or less. Many times, developers find that they cannot reproduce their
issues this way, which is a good indicator that the bug is in their own
code.
</li>
<li>
Search the issue tracker at
<a href="http://www.crbug.com">http://www.crbug.com</a> to see whether
someone has reported a similar issue. Most issues related to
extensions are filed under <strong>Feature=Extensions</strong>, so to
look for an extension bug related to the
chrome.tabs.executeScript function (for example), search for
"<code>Feature=Extensions Type=Bug chrome.tabs.executeScript</code>",
which will give you
<a href="http://code.google.com/p/chromium/issues/list?can=2&q=Feature%3DExtensions+Type%3DBug+chrome.tabs.executeScript&colspec=ID+Stars+Pri+Area+Feature+Type+Status+Summary+Modified+Owner+Mstone+OS&x=mstone&y=area&cells=tiles">
this list of results</a>.
</li>
<li>
If you find a bug that describes your issue, click the star icon to be
notified when the bug receives an update. <em>Do not respond to the
bug to say "me too" or ask "when will this be fixed?"</em>; such updates
can cause hundreds of emails to be sent. Add a comment only if you have
information (such as a better test case or a suggested fix) that is likely
to be helpful.
</li>
<li>
If you found no appropriate bug to star, file a new issue report at
<a href="http://new.crbug.com">http://new.crbug.com</a>. Be as explicit
as possible when filling out this form: choose a descriptive title,
explain the steps to reproduce the bug, and describe the expected and
actual behavior. Attach your test example to the report and add
screenshots if appropriate. The easier your report makes it for others
to reproduce your issue, the greater chance that your bug will be fixed
promptly.
</li>
<li>
Wait for the bug to be updated. Most new bugs are triaged within a week,
although it can sometimes take longer for an update. <em>Do not reply
to the bug to ask when the issue will be fixed.</em> If your bug has not
been modified after two weeks, please post a message to the
<a href="http://groups.google.com/a/chromium.org/group/chromium-extensions/topics">
discussion group</a> with a link back to your bug.
</li>
<li>
If you originally reported your bug on the discussion group and were
directed to this FAQ entry, reply to your original thread with a link
to the bug you starred or reported. This will make it easier for others
experiencing the same issue to find the correct bug.
</li>
</ol>
<h3 id="faq-fea-02">I have a feature request! How can I report it?</h3>
<p>If you identify a feature (especially if it's related to an experimental
API) that could be added to improve the extension development experience,
make sure an appropriate request is filed in the issue tracker.</p>
<p>The steps you should follow to ensure this are:</p>
<ol>
<li>
Search the issue tracker at
<a href="http://www.crbug.com">http://www.crbug.com</a> to see whether
someone has requested a similar feature. Most requests related to
extensions are filed under <strong>Feature=Extensions</strong>, so to
look for an extension feature request related to keyboard shortcuts
(for example), search
for "<code>Feature=Extensions Type=Feature shortcuts</code>",
which will give you
<a href="http://code.google.com/p/chromium/issues/list?can=2&q=Feature%3DExtensions+Type%3DFeature+shortcuts&colspec=ID+Stars+Pri+Area+Feature+Type+Status+Summary+Modified+Owner+Mstone+OS&x=mstone&y=area&cells=tiles">
this list of results</a>.
</li>
<li>
If you find a ticket that matches your request, click the star icon to be
notified when the bug receives an update. <em>Do not respond to the
bug to say "me too" or ask "when will this be implemented?"</em>; such
updates can cause hundreds of emails to be sent.
</li>
<li>
If you found no appropriate ticket to star, file a new request at
<a href="http://new.crbug.com">http://new.crbug.com</a>. Be as detailed
as possible when filling out this form: choose a descriptive title
and explain exactly what feature you would like and how you plan to use it.
</li>
<li>
Wait for the ticket to be updated. Most new requests are triaged within a
week, although it can sometimes take longer for an update. <em>Do not reply
to the ticket to ask when the feature will be added.</em> If your
ticket has not been modified after two weeks, please post a message to the
<a href="http://groups.google.com/a/chromium.org/group/chromium-extensions/topics">
discussion group</a> with a link back to your request.
</li>
<li>
If you originally reported your request on the discussion group and were
directed to this FAQ entry, reply to your original thread with a link
to the ticket you starred or opened. This will make it easier for others
with the same request to find the correct ticket.
</li>
</ol>
</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 -->
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