docs/static/faq.html

<div id="pageData-name" class="pageData">Frequently Asked Questions</div>


<!-- <div id="pageData-showTOC" class="pageData">true</div> -->

<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
<a href="http://www.google.com/support/chrome/bin/answer.py?answer=113909">gallery help</a>.
<!-- PENDING: add a link to store help -->
</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-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><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><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&mdash;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>