path: root/chrome/common/extensions/docs/static/faq.html

<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://groups.google.com/a/chromium.org/group/chromium-extensions">group</a> or the
<a href="http://www.google.com/support/chrome/bin/answer.py?answer=113909">gallery help</a>.
</p>

<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-gen-02">What technologies are used to write extensions for Google Chrome?</a></li>
        <li><a href="#faq-gen-03">Are extensions fetched from the web every time the browser is loaded?</a></li>
      </ul>
<h4>Development</h4>
      <ul>
        <li><a href="#faq-dev-01">How can I set up Google Chrome for extension development?</a></li>
        <li><a href="#faq-dev-02">Can I make cross-domain Ajax requests in an extension?</a></li>
        <li><a href="#faq-dev-03">Can I use 3rd party web services in my extension?</a></li>
        <li><a href="#faq-dev-04">Can I use OAuth in my extensions?</a></li>
        <li><a href="#faq-dev-05">What UI controls can I create for my extension?</a></li>
        <li><a href="#faq-dev-06">Can I load DLLs in my extension?</a></li>
        <li><a href="#faq-dev-07">Can Google Chrome Extensions encode/decode JSON data?</a></li>
        <li><a href="#faq-dev-08">Can I store data locally in 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">Can I create an options menu for my application?</a></li>
        <li><a href="#faq-dev-11">Can two extensions communicate with each other?</a></li>
        <li><a href="#faq-dev-12">What debugging tools are available to extension developers?</a></li>
        <li><a href="#faq-dev-13">Can extensions use Google Analytics?</a></li>
        <li><a href="#faq-dev-14">How do I determine which version of Google Chrome is deployed to which channel?</a></li>
        <li><a href="#faq-dev-15">Can I add a content script to chrome:// URLs?</a></li>
        <li><a href="#faq-dev-16">Why do wildcard matches not work for top level domains (TLDs)?</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 Google
  Chrome browser and provide additional functionality, integration with third
  party websites or services, and customized browsing experiences.
</p>

<h3 id="faq-gen-02">What technologies are used to write extensions for Google Chrome?</h3>
<p>
  Google Chrome 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 Google 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 Google 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>


<h2>Development</h2>


<h3 id="faq-dev-01">How can I set up Google Chrome for extension development?</h3>
<p>
  As long as you are using a version of Google Chrome that supports
  extensions, you already have everything you need to start writing an
  extension of your own. Select "Extensions" from the Tools menu
  <img style="vertical-align: middle;" src="images/toolsmenu.gif" /> (or from
  the window menu on Mac) and click "Developer Mode". From there, you can load
  an unpacked directory of files as if it were a packaged extension, reload
  extensions, and more. For a complete tutorial, please view
  <a href="http://code.google.com/chrome/extensions/getstarted.html">this getting started guide</a>.
</p>

<h3 id="faq-dev-02">Can I make cross-domain Ajax requests in an extension?</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 I use 3rd party web services in my extension?</h3>
<p>
  Yes. Google Chrome Extensions are capable of making cross-domain Ajax
  requests, so they can call remote APIs directly. APIs which provide data
  in JSON format are particularly easy to use.
</p>

<h3 id="faq-dev-04">Can I use OAuth in my extensions?</h3>
<p>
  Absolutely, there are extensions which 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-05">What UI controls can I create 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, your extension may add buttons
  to the Google Chrome browser itself.  See
  <a href="http://code.google.com/chrome/extensions/browserAction.html">browser actions</a>
  and
  <a href="http://code.google.com/chrome/extensions/pageAction.html">page actions</a>
  for more information.
</p>

<h3 id="faq-dev-06">Can I load DLLs in my extension?</h3>
<p>
  Yes, using the
  <a href="http://code.google.com/chrome/extensions/trunk/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.
</p>

<h3 id="faq-dev-07">Can Google Chrome Extensions encode/decode JSON data?</h3>
<p>
  Yes, because V8 (Google 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 I store data locally in my extension?</h3>
<p>
  Yes, extensions can use <a href="http://dev.w3.org/html5/webstorage/">localStorage</a>
  to store string data permanently. Using Google Chrome's built-in JSON
  functions, you can store complex data structures in localStorage.  For
  extensions which have the need to execute SQL queries on their stored data,
  Google 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-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">Can 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-11">Can two extensions communicate with each other?</h3>
<p>
  Extensions may pass messages to other extensions. See the
  <a href="http://code.google.com/chrome/extensions/trunk/messaging.html#external">message passing documentation</a>
  for more information.
</p>

<h3 id="faq-dev-12">What debugging tools are available to extension developers?</h3>
<p>
  Google 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-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-14">How do I determine which version of Google Chrome is deployed to which channel?</h3>
<p>
  To determine which version of Google 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,#.#.###.#
cf,beta,#.#.###.#
cf,stable,#.#.###.#
linux,dev,#.#.###.#
linux,beta,#.#.###.#
linux,stable,#.#.###.#
mac,dev,#.#.###.#
mac,beta,#.#.###.#
mac,stable,#.#.###.#
win,dev,#.#.###.#
win,beta,#.#.###.#
win,stable,#.#.###.#</pre>
<p>
  Each line represents a different platform and channel combination. The
  listed platforms are <code>cf</code> (Google Chrome Frame),
  <code>linux</code>, <code>mac</code>, and <code>win</code>.  The listed
  channels are <code>dev</code>, <code>beta</code>, and <code>stable</code>.
  The four-part number at the end of each line represents the version of Google
  Chrome currently deployed to that platform-channel combination.
</p>

<h3 id="faq-dev-15">Can I add a content script to 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-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>