chrome/common/extensions/docs/overview.html - Issue 10642015: Basic setup for generating app docs

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Issue 10642015: Basic setup for generating app docs (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src

Patch Set: fix Created 8 years, 6 months ago

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Index: chrome/common/extensions/docs/overview.html

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-<!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="../../../../third_party/json_minify/minify-sans-regexp.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>Overview - Google Chrome Extensions - Google Code</title></head>

- <body> <div id="devModeWarning" class="displayModeWarning">

- 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>

- <div id="branchWarning" class="displayModeWarning">

- <span>WARNING: This is the <span id="branchName">BETA</span> documentation.

- It may not work with the stable release of Chrome.</span>

- <select id="branchChooser">

- <option>Choose a different version...

- </option><option value="">Stable

- </option><option value="beta">Beta

- </option><option value="dev">Dev

- </option><option value="trunk">Trunk

- </option></select>

- </div>

- <div id="unofficialWarning" class="displayModeWarning">

- <span>WARNING: This is unofficial documentation. It may not work with the

- current release of Chrome.</span>

- <button id="goToOfficialDocs">Go to the official docs</button>

- </div>

- <div id="gc-container" class="labs">

-

- <!-- 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" -->

-

- <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>

-

- <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="https://www.google.com/jsapi"></script>

- <script type="text/javascript">google.load("elements", "1", {packages: "transliteration"});</script>

- <script type="text/javascript" src="https://www.google.com/coop/cse/t13n?form=cse&t13n_langs=en"></script>

- <script type="text/javascript" src="https://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>

- <li id="so_link">

- <a href="http://stackoverflow.com/questions/tagged/google-chrome-extension" title="[google-chrome-extension] tag on Stack Overflow">Questions?</a>

- </li>

- </ul>

- </div>

- <div class="g-section g-tpl-170">

-

- <div class="g-unit g-first" id="gc-toc">

- <ul>

- <li><a href="getstarted.html">Getting Started</a></li>

- <li class="leftNavSelected">Overview</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="devtools.html">Developer Tools</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><a href="background_pages.html">Background Pages</a></li>

- <li><a href="content_scripts.html">Content Scripts</a></li>

- <li><a href="xhr.html">Cross-Origin XHR</a></li>

- <li><a href="i18n.html">Internationalization</a></li>

- <li><a href="messaging.html">Message Passing</a></li>

- <li><a href="permissions.html">Optional Permissions</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">Overview</h1>

- </div>

-

- <div id="toc">

- <h2>Contents</h2>

- <ol>

- <li>

- <a href="#what">The basics</a>

- <ol>

- <li>

- <a href="#extension-ui">Extension UIs</a>

- </li><li>

- <a href="#packagedapp-ui">Packaged app UIs</a>

- </li>

- </ol>

- </li><li>

- <a href="#files">Files</a>

- <ol>

- <li>

- <a href="#relative-urls">Referring to files</a>

- </li><li>

- <a href="#H3-5">The manifest file</a>

- </li>

- </ol>

- </li><li>

- <a href="#arch">Architecture</a>

- <ol>

- <li>

- <a href="#background_page">The background page</a>

- </li><li>

- <a href="#pages">UI pages</a>

- </li><li>

- <a href="#contentScripts">Content scripts</a>

- </li>

- </ol>

- </li><li>

- <a href="#apis"> Using the chrome.* APIs </a>

- <ol>

- <li>

- <a href="#sync"> Asynchronous vs. synchronous methods </a>

- </li><li>

- <a href="#sync-example"> Example: Using a callback </a>

- </li><li>

- <a href="#chrome-more"> More details </a>

- </li>

- </ol>

- </li><li>

- <a href="#pageComm">Communication between pages </a>

- <ol>

- </ol>

- </li><li>

- <a href="#incognito"> Saving data and incognito mode </a>

- <ol>

- </ol>

- </li><li>

- <a href="#now-what"> Now what? </a>

- <ol>

- </ol>

- </li>

- </ol>

- </div>

-

-

-

- <div id="static"><div id="pageData-name" class="pageData">Overview</div>

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

-<p>

-Once you've finished this page

-and the

-<a href="getstarted.html">Getting Started</a> tutorial,

-you'll be all set to start writing extensions and packaged apps.

-</p>

-<p class="caution">

-<strong>Note:</strong>

-<em>Packaged apps</em> are implemented as extensions,

-so unless otherwise stated,

-everything in this page applies to packaged apps.

-</p>

-<h2 id="what">The basics</h2>

-<p>

-An extension is a zipped bundle of files—HTML,

-CSS, JavaScript, images, and anything else you need—that

-adds functionality to the Google Chrome browser.

-Extensions are essentially web pages,

-and they can use all the

-<a href="api_other.html">APIs that the browser provides to web pages</a>,

-from XMLHttpRequest to JSON to HTML5.

-</p>

-<p>

-Extensions can interact with web pages or servers using

-<a href="content_scripts.html">content scripts</a> or

-<a href="xhr.html">cross-origin XMLHttpRequests</a>.

-Extensions can also interact programmatically

-with browser features such as

-<a href="bookmarks.html">bookmarks</a>

-and <a href="tabs.html">tabs</a>.

-</p>

-<h3 id="extension-ui">Extension UIs</h3>

-<p>

-Many extensions—but not packaged apps—add

-UI to Google Chrome in the form of

-<a href="browserAction.html">browser actions</a>

-or <a href="pageAction.html">page actions</a>.

-Each extension can have at most one browser action or page action.

-Choose a <b>browser action</b> when the extension is relevant to most pages.

-Choose a <b>page action</b> when the extension's icon

-should appear or disappear,

-depending on the page.

-</p>

-<table class="columns">

-<tbody><tr>

- <td width="33%">

- <img src="images/overview/browser-action.png" width="147" height="100" alt="screenshot">

- </td>

- <td width="33%">

- <img src="images/overview/page-action.png" width="147" height="100" alt="screenshot">

- </td>

- <td>

- <img src="images/overview/browser-action-with-popup.png" width="147" height="100" alt="screenshot">

- </td>

-</tr>

-<tr>

- <td>

- This <a href="samples.html#gmail">mail extension</a>

- uses a <em>browser action</em>

- (icon in the toolbar).

- </td>

- <td>

- This <a href="samples.html#mappy">map extension</a>

- uses a <em>page action</em>

- (icon in the address bar)

- and <em>content script</em>

- (code injected into a web page).

- </td>

- <td>

- This <a href="samples.html#news">news extension</a>

- features a browser action that,

- when clicked,

- shows a <em>popup</em>.

- </td>

-</tr>

-</tbody></table>

-<p>

-Extensions (and packaged apps) can also present a UI in other ways,

-such as adding to the Chrome context menu,

-providing an options page,

-or using a content script that changes how pages look.

-See the <a href="devguide.html">Developer's Guide</a>

-for a complete list of extension features,

-with links to implementation details

-for each one.

-</p>

-<h3 id="packagedapp-ui">Packaged app UIs</h3>

-<p>

-A packaged app usually presents its main functionality using

-an HTML page that's bundled into the app.

-For example, the following packaged app

-displays a Flash file within an HTML page.

-</p>

-<img src="images/overview/flash-app.png" width="372" height="300" alt="screenshot">

-<p>

-For more information,

-see <a href="apps.html">Packaged Apps</a>.

-</p>

-<h2 id="files">Files</h2>

-<p>

-Each extension has the following files:

-

-</p>

-<ul>

- <li>A <b>manifest file</b></li>

- <li>One or more <b>HTML files</b> (unless the extension is a theme)</li>

- <li><em>Optional:</em> One or more <b>JavaScript files</b></li>

- <li><em>Optional:</em> Any other files your extension needs—for

- example, image files</li>

-</ul>

-<p>

-While you're working on your extension,

-you put all these files into a single folder.

-When you distribute your extension,

-the contents of the folder are packaged into a special ZIP file

-that has a <code>.crx</code> suffix.

-If you upload your extension using the

-<a href="https://chrome.google.com/webstore/developer/dashboard">Chrome Developer Dashboard</a>,

-the <code>.crx</code> file is created for you.

-For details on distributing extensions,

-see <a href="hosting.html">Hosting</a>.

-</p>

-<h3 id="relative-urls">Referring to files</h3>

-<p>

-You can put any file you like into an extension,

-but how do you use it?

-Usually,

-you can refer to the file using a relative URL,

-just as you would in an ordinary HTML page.

-Here's an example of referring to

-a file named <code>myimage.png</code>

-that's in a subfolder named <code>images</code>.

-</p>

-<pre><img <b>src="images/myimage.png"</b>>

-</pre>

-<p>

-As you might notice while you use the Google Chrome debugger,

-every file in an extension is also accessible by an absolute URL like this:

-</p>

-<blockquote>

-<b>chrome-extension://</b><em><extensionID></em><b>/</b><em><pathToFile></em>

-</blockquote>

-<p>

-In that URL, the <em><extensionID></em> is a unique identifier

-that the extension system generates for each extension.

-You can see the IDs for all your loaded extensions

-by going to the URL <b>chrome://extensions</b>.

-The <em><pathToFile></em> is the location of the file

-under the extension's top folder;

-it's the same as the relative URL.

-</p>

-<p>

-While you're working on an extension

-(before it's packaged),

-the extension ID can change.

-Specifically, the ID of an unpacked extension will change

-if you load the extension from a different directory;

-the ID will change again when you package the extension.

-If your extension's code

-needs to specify the full path to a file within the extension,

-you can use the <code>@@extension_id</code>

-<a href="i18n.html#overview-predefined">predefined message</a>

-to avoid hardcoding the ID during development.

-</p>

-<p>

-When you package an extension

-(typically, by uploading it with the dashboard),

-the extension gets a permanent ID,

-which remains the same even after you update the extension.

-Once the extension ID is permanent,

-you can change all occurrences of

-<code>@@extension_id</code> to use the real ID.

-</p>

-<a name="H3-5"></a><h3>The manifest file</h3>

-<p>

-The manifest file, called <code>manifest.json</code>,

-gives information about the extension,

-such as the most important files

-and the capabilities that the extension might use.

-Here's a typical manifest file for a browser action

-that uses information from google.com:

-</p>

-<pre>{

- "name": "My Extension",

- "version": "2.1",

- "description": "Gets information from Google.",

- "icons": { "128": "icon_128.png" },

- "background": {

- "scripts": ["bg.js"]

- },

- "permissions": ["http://*.google.com/", "https://*.google.com/"],

- "browser_action": {

- "default_title": "",

- "default_icon": "icon_19.png",

- "default_popup": "popup.html"

- }

-}</pre>

-<p>

-For details, see

-<a href="manifest.html">Manifest Files</a>.

-</p>

-<h2 id="arch">Architecture</h2>

-<p>

-Many extensions have a <em>background page</em>,

-an invisible page

-that holds the main logic of the extension.

-An extension can also contain other pages

-that present the extension's UI.

-If an extension needs to interact with web pages that the user loads

-(as opposed to pages that are included in the extension),

-then the extension must use a content script.

-</p>

-<h3 id="background_page">The background page</h3>

-<p>

-The following figure shows a browser

-that has at least two extensions installed:

-a browser action (yellow icon)

-and a page action (blue icon).

-Both the browser action and the page action

-have background pages.

-This figure shows the browser action's background page,

-which is defined by <code>background.html</code>

-and has JavaScript code that controls

-the behavior of the browser action in both windows.

-</p>

-<img src="images/overview/arch-1.gif" width="232" height="168" alt="Two windows and a box representing a background page (background.html). One window has a yellow icon; the other has both a yellow icon and a blue icon. The yellow icons are connected to the background page.">

-<p>

-Although background pages can be useful,

-don't use one if you don't need it.

-Background pages are always open,

-so when a user installs many extensions that have background pages,

-Chrome's performance can suffer.

-</p>

-<!-- PENDING: Perhaps show a picture of many background page processes.

- This could build on a figure that shows the process architecture,

- and perhaps the differences between packaged apps and extensions. -->

-<p>

-Here are some examples of extensions that usually

-<em>do not need</em> a background page:

-</p>

-<ul>

- <li> An extension with a browser action that

- presents its UI solely through a popup

- (and perhaps an options page).

- </li>

- <li>

- An extension that provides an <em>override page</em>—a

- page that replaces a standard Chrome page.

- </li>

- <li>

- An extension with a content script

- that <em>doesn't use</em> localStorage or

- <a href="#apis">extension APIs</a>.

- </li>

- <li>

- An extension that has no UI except for an options page.

- </li>

-</ul>

-<p>

-See <a href="background_pages.html">Background Pages</a>

-for more details.

-</p>

-<h3 id="pages">UI pages</h3>

-<p>

-Extensions can contain ordinary HTML pages that display the extension's UI.

-For example, a browser action can have a popup,

-which is implemented by an HTML file.

-Any extension can have an options page,

-which lets users customize how the extension works.

-Another type of special page is the override page.

-And finally, you can

-use <a href="tabs.html#method-create">chrome.tabs.create()</a>

-or <code>window.open()</code>

-to display any other HTML files that are in the extension.

-</p>

-<p>

-The HTML pages inside an extension

-have complete access to each other's DOMs,

-and they can invoke functions on each other.

-</p>

-<!-- PENDING: Change the following example and figure

-to use something that's not a popup?

-(It might lead people to think that popups need background pages.) -->

-<p>

-The following figure shows the architecture

-of a browser action's popup.

-The popup's contents are a web page

-defined by an HTML file

-(<code>popup.html</code>).

-This extension also happens to have a background page

-(<code>background.html</code>).

-The popup doesn't need to duplicate code

-that's in the background page

-because the popup can invoke functions on the background page.

-</p>

-<img src="images/overview/arch-2.gif" width="256" height="168" alt="A browser window containing a browser action that's displaying a popup. The popup's HTML file (popup.html) can communicate with the extension's background page (background.html).">

-<p>

-See <a href="browserAction.html">Browser Actions</a>,

-<a href="options.html">Options</a>,

-<a href="override.html">Override Pages</a>,

-and the <a href="#pageComm">Communication between pages</a> section

-for more details.

-</p>

-<h3 id="contentScripts">Content scripts</h3>

-<p>

-If your extension needs to interact with web pages,

-then it needs a <em>content script</em>.

-A content script is some JavaScript

-that executes in the context of a page

-that's been loaded into the browser.

-Think of a content script as part of that loaded page,

-not as part of the extension it was packaged with

-(its <em>parent extension</em>).

-</p>

-<!-- [PENDING: Consider explaining that the reason content scripts are separated from the extension is due to chrome's multiprocess design. Something like:

-Each extension runs in its own process.

-To have rich interaction with a web page, however,

-the extension must be able to

-run some code in the web page's process.

-Extensions accomplish this with content scripts.]

--->

-<p>

-Content scripts can read details of the web pages the browser visits,

-and they can make changes to the pages.

-In the following figure,

-the content script

-can read and modify

-the DOM for the displayed web page.

-It cannot, however, modify the DOM of its parent extension's background page.

-</p>

-<img src="images/overview/arch-3.gif" width="238" height="169" alt="A browser window with a browser action (controlled by background.html) and a content script (controlled by contentscript.js).">

-<p>

-Content scripts aren't completely cut off from their parent extensions.

-A content script can exchange messages with its parent extension,

-as the arrows in the following figure show.

-For example, a content script might send a message

-whenever it finds an RSS feed in a browser page.

-Or a background page might send a message

-asking a content script to change the appearance of its browser page.

-</p>

-<img src="images/overview/arch-cs.gif" width="238" height="194" alt="Like the previous figure, but showing more of the parent extension's files, as well as a communication path between the content script and the parent extension.">

-

-<p>

-For more information,

-see <a href="content_scripts.html">Content Scripts</a>.

-</p>

-<h2 id="apis"> Using the chrome.* APIs </h2>

-<p>

-In addition to having access to all the APIs that web pages and apps can use,

-extensions can also use Chrome-only APIs

-(often called <em>chrome.* APIs</em>)

-that allow tight integration with the browser.

-For example, any extension or web app can use the

-standard <code>window.open()</code> method to open a URL.

-But if you want to specify which window that URL should be displayed in,

-your extension can use the Chrome-only

-<a href="tabs.html#method-create">chrome.tabs.create()</a>

-method instead.

-</p>

-<h3 id="sync"> Asynchronous vs. synchronous methods </h3>

-<p>

-Most methods in the chrome.* APIs are <b>asynchronous</b>:

-they return immediately, without waiting for the operation to finish.

-If you need to know the outcome of that operation,

-then you pass a callback function into the method.

-That callback is executed later (potentially <em>much</em> later),

-sometime after the method returns.

-Here's an example of the signature for an asynchronous method:

-</p>

-<p>

-<code>

-chrome.tabs.create(object <em>createProperties</em>, function <em>callback</em>)

-</code>

-</p>

-<p>

-Other chrome.* methods are <b>synchronous</b>.

-Synchronous methods never have a callback

-because they don't return until they've completed all their work.

-Often, synchronous methods have a return type.

-Consider the

-<a href="extension.html#method-getBackgroundPage">chrome.extensions.getBackgroundPage()</a> method:

-</p>

-<p>

-<code>

-Window chrome.extension.getBackgroundPage()

-</code>

-</p>

-<p>

-This method has no callback and a return type of <code>Window</code>

-because it synchronously returns the background page

-and performs no other, asynchronous work.

-</p>

-<h3 id="sync-example"> Example: Using a callback </h3>

-<p>

-Say you want to navigate

-the user's currently selected tab to a new URL.

-To do this, you need to get the current tab's ID

-(using <a href="tabs.html#method-getSelected">chrome.tabs.getSelected()</a>)

-and then make that tab go to the new URL

-(using <a href="tabs.html#method-update">chrome.tabs.update()</a>).

-</p>

-<p>

-If <code>getSelected()</code> were synchronous,

-you might write code like this:

-</p>

-<pre> <b>//THIS CODE DOESN'T WORK</b>

-<span class="linenumber">1: </span>var tab = chrome.tabs.getSelected(null); <b>//WRONG!!!</b>

-<span class="linenumber">2: </span>chrome.tabs.update(tab.id, {url:newUrl});

-<span class="linenumber">3: </span>someOtherFunction();

-</pre>

-<p>

-That approach fails

-because <code>getSelected()</code> is asynchronous.

-It returns without waiting for its work to complete,

-and it doesn't even return a value

-(although some asynchronous methods do).

-You can tell that <code>getSelected()</code> is asynchronous

-by the <em>callback</em> parameter in its signature:

-</p><p>

-<code>

-chrome.tabs.getSelected(integer <em>windowId</em>, function <em>callback</em>)

-</code>

-</p>

-<p>

-To fix the preceding code,

-you must use that callback parameter.

-The following code shows

-how to define a callback function

-that gets the results from <code>getSelected()</code>

-(as a parameter named <code>tab</code>)

-and calls <code>update()</code>.

-</p>

-<pre> <b>//THIS CODE WORKS</b>

-<span class="linenumber">1: </span>chrome.tabs.getSelected(null, <b>function(tab) {</b>

-<span class="linenumber">2: </span> chrome.tabs.update(tab.id, {url:newUrl});

-<span class="linenumber">3: </span><b>}</b>);

-<span class="linenumber">4: </span>someOtherFunction();

-</pre>

-<p>

-In this example, the lines are executed in the following order: 1, 4, 2.

-The callback function specified to <code>getSelected</code> is called

-(and line 2 executed)

-only after information about the currently selected tab is available,

-which is sometime after <code>getSelected()</code> returns.

-Although <code>update()</code> is asynchronous,

-this example doesn't use its callback parameter,

-since we don't do anything about the results of the update.

-</p>

-<h3 id="chrome-more"> More details </h3>

-<p>

-For more information, see the

-<a href="api_index.html">chrome.* API docs</a>

-and watch this video:

-</p>

-<p>

-<iframe title="YouTube video player" width="640" height="390" src="http://www.youtube.com/embed/bmxr75CV36A?rel=0" frameborder="0" allowfullscreen=""></iframe>

-</p>

-<h2 id="pageComm">Communication between pages </h2>

-<p>

-The HTML pages within an extension often need to communicate.

-

-Because all of an extension's pages

-execute in same process on the same thread,

-the pages can make direct function calls to each other.

-</p>

-<p>

-To find pages in the extension, use

-<a href="extension.html"><code>chrome.extension</code></a>

-methods such as

-<code>getViews()</code> and

-<code>getBackgroundPage()</code>.

-Once a page has a reference to other pages within the extension,

-the first page can invoke functions on the other pages,

-and it can manipulate their DOMs.

-</p>

-

-<h2 id="incognito"> Saving data and incognito mode </h2>

-<p>

-Extensions can save data using

-the HTML5 <a href="http://dev.w3.org/html5/webstorage/">web storage API</a>

-(such as <code>localStorage</code>)

-or by making server requests that result in saving data.

-Whenever you want to save something,

-first consider whether it's

-from a window that's in incognito mode.

-By default, extensions don't run in incognito windows,

-and packaged apps <em>do</em>.

-You need to consider what a user expects

-from your extension or packaged app

-when the browser is incognito.

-</p>

-<p>

-<em>Incognito mode</em> promises that the window will leave no tracks.

-When dealing with data from incognito windows,

-do your best to honor this promise.

-For example, if your extension normally

-saves browsing history to the cloud,

-don't save history from incognito windows.

-On the other hand, you can store

-your extension's settings from any window,

-incognito or not.

-</p>

-<p class="note">

-<b>Rule of thumb:</b>

-If a piece of data might show where a user

-has been on the web or what the user has done,

-don't store it if it's from an incognito window.

-</p>

-<p>

-To detect whether a window is in incognito mode,

-check the <code>incognito</code> property of the relevant

-<a href="tabs.html#type-Tab">Tab</a> or

-<a href="windows.html#type-Window">Window</a> object.

-For example:

-</p>

-<pre>var bgPage = chrome.extension.getBackgroundPage();

-function saveTabData(tab, data) {

- if (tab.incognito) {

- bgPage[tab.url] = data; // Persist data ONLY in memory

- } else {

- localStorage[tab.url] = data; // OK to store data

-</pre>

-<h2 id="now-what"> Now what? </h2>

-<p>

-Now that you've been introduced to extensions,

-you should be ready to write your own.

-Here are some ideas for where to go next:

-</p>

-<ul>

- <li> <a href="getstarted.html">Tutorial: Getting Started</a> </li>

- <li> <a href="tut_debugging.html">Tutorial: Debugging</a> </li>

- <li> <a href="devguide.html">Developer's Guide</a> </li>

- <li> <a href="http://dev.chromium.org/developers/design-documents/extensions/samples">Samples</a> </li>

- <li> <a href="http://www.youtube.com/view_play_list?p=CA101D6A85FE9D4B">Videos</a>,

- such as

- <a href="http://www.youtube.com/watch?v=B4M_a7xejYI&feature=PlayList&p=CA101D6A85FE9D4B&index=6">Extension Message Passing</a>

- </li>

-</ul>

-</div>

-

-

- </div>

- </div>

- </div>

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