chrome/common/extensions/docs/messaging.html - chromium/src - Git at Google

 <!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>Message Passing - 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">
       <!-- SUBTEMPLATES: DO NOT MOVE FROM THIS LOCATION -->
       <!-- 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" -->
        <!-- /SUBTEMPLATES -->
   <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>
     <!-- API HEADER -->
     <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&amp;t13n_langs=en"></script>
           <script type="text/javascript" src="https://www.google.com/coop/cse/brand?form=cse&amp;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> <!-- end gc-topnav -->
     <div class="g-section g-tpl-170">
       <!-- SIDENAV -->
       <div class="g-unit g-first" id="gc-toc">
         <ul>
           <li><a href="getstarted.html">Getting Started</a></li>
           <li><a href="overview.html">Overview</a></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 class="leftNavSelected">Message Passing</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">Message Passing</h1>
       </div>
         <!-- TABLE OF CONTENTS -->
         <div id="toc">
           <h2>Contents</h2>
           <ol>
             <li>
               <a href="#simple">Simple one-time requests</a>
               <ol>
               </ol>
             </li><li>
               <a href="#connect">Long-lived connections</a>
               <ol>
               </ol>
             </li><li>
               <a href="#external">Cross-extension messaging</a>
               <ol>
               </ol>
             </li><li>
               <a href="#security-considerations">Security considerations</a>
               <ol>
               </ol>
             </li><li>
               <a href="#examples">Examples</a>
               <ol>
               </ol>
             </li>
           </ol>
         </div>
         <!-- /TABLE OF CONTENTS -->
         <!-- Standard content lead-in for experimental API pages -->
         <!-- STATIC CONTENT PLACEHOLDER -->
         <div id="static"><div id="pageData-name" class="pageData">Message Passing</div>
 <div id="pageData-showTOC" class="pageData">true</div>
 <p>
 Since content scripts run in the context of a web page and not the extension,
 they often need some way of communicating with the rest of the extension. For
 example, an RSS reader extension might use content scripts to detect the
 presence of an RSS feed on a page, then notify the background page in order to
 display a page action icon for that page.
 </p><p>
 Communication between extensions and their content scripts works by using
 message passing. Either side can listen for messages sent from the other end,
 and respond on the same channel. A message can contain any valid JSON object
 (null, boolean, number, string, array, or object). There is a simple API for
 <a href="#simple">one-time requests</a>
 and a more complex API that allows you to have
 <a href="#connect">long-lived connections</a>
 for exchanging multiple messages with a shared context. It is also possible to
 send a message to another extension if you know its ID, which is covered in
 the
 <a href="#external">cross-extension messages</a>
 section.
 </p><h2 id="simple">Simple one-time requests</h2>
 <p>
 If you only need to send a single message to another part of your extension
 (and optionally get a response back), you should use the simplified
 <a href="extension.html#method-sendRequest">chrome.extension.sendRequest()</a>
 or
 <a href="tabs.html#method-sendRequest">chrome.tabs.sendRequest()</a>
 methods. This lets you send a one-time JSON-serializable message from a
 content script to extension, or vice versa, respectively. An optional
 callback parameter allows you handle the response from the other side, if
 there is one.
 </p><p>
 Sending a request from a content script looks like this:
 </p><pre>contentscript.js
 ================
 chrome.extension.sendRequest({greeting: "hello"}, function(response) {
   console.log(response.farewell);
 });
 </pre>
 <p>
 Sending a request from the extension to a content script looks very similar,
 except that you need to specify which tab to send it to. This example
 demonstrates sending a message to the content script in the selected tab.
 </p><pre>background.html
 ===============
 chrome.tabs.getSelected(null, function(tab) {
   chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
     console.log(response.farewell);
   });
 });
 </pre>
 <p>
 On the receiving end, you need to set up an
 <a href="extension.html#event-onRequest">chrome.extension.onRequest</a>
 event listener to handle the message. This looks the same from a content
 script or extension page.
 </p><pre>chrome.extension.onRequest.addListener(
   function(request, sender, sendResponse) {
     console.log(sender.tab ?
                 "from a content script:" + sender.tab.url :
                 "from the extension");
     if (request.greeting == "hello")
       sendResponse({farewell: "goodbye"});
   });
 </pre>
 <p class="note">
 <b>Note:</b> If multiple pages are listening for onRequest events, only the
 first to call sendResponse() for a particular event will succeed in sending the
 response. All other responses to that event will be ignored.
 </p>
 <h2 id="connect">Long-lived connections</h2>
 <p>
 Sometimes it's useful to have a conversation that lasts longer than a single
 request and response. In this case, you can open a long-lived channel from
 your content script to an extension page, or vice versa, using
 <a href="extension.html#method-connect">chrome.extension.connect()</a>
 or
 <a href="tabs.html#method-connect">chrome.tabs.connect()</a> respectively. The
 channel can optionally have a name, allowing you to distinguish between
 different types of connections.
 </p><p>
 One use case might be an automatic form fill extension. The content script
 could open a channel to the extension page for a particular login, and send a
 message to the extension for each input element on the page to request the
 form data to fill in. The shared connection allows the extension to keep
 shared state linking the several messages coming from the content script.
 </p><p>
 When establishing a connection, each end is given a
 <a href="extension.html#type-Port">Port</a>
 object which is used for sending and receiving messages through that
 connection.
 </p><p>
 Here is how you open a channel from a content script, and send and listen for
 messages:
 </p><pre>contentscript.js
 ================
 var port = chrome.extension.connect({name: "knockknock"});
 port.postMessage({joke: "Knock knock"});
 port.onMessage.addListener(function(msg) {
   if (msg.question == "Who's there?")
     port.postMessage({answer: "Madame"});
   else if (msg.question == "Madame who?")
     port.postMessage({answer: "Madame... Bovary"});
 });
 </pre>
 <p>
 Sending a request from the extension to a content script looks very similar,
 except that you need to specify which tab to connect to. Simply replace the
 call to connect in the above example with
 <a href="tabs.html#method-connect">chrome.tabs.connect(tabId, {name:
 "knockknock"})</a>.
 </p><p>
 In order to handle incoming connections, you need to set up a
 <a href="extension.html#event-onConnect">chrome.extension.onConnect</a>
 event listener. This looks the same from a content script or an extension
 page. When another part of your extension calls "connect()", this event is
 fired, along with the
 <a href="extension.html#type-Port">Port</a>
 object you can use to send and receive messages through the connection. Here's
 what it looks like to respond to incoming connections:
 </p><pre>chrome.extension.onConnect.addListener(function(port) {
   console.assert(port.name == "knockknock");
   port.onMessage.addListener(function(msg) {
     if (msg.joke == "Knock knock")
       port.postMessage({question: "Who's there?"});
     else if (msg.answer == "Madame")
       port.postMessage({question: "Madame who?"});
     else if (msg.answer == "Madame... Bovary")
       port.postMessage({question: "I don't get it."});
   });
 });
 </pre>
 <p>
 You may want to find out when a connection is closed, for example if you are
 maintaining separate state for each open port. For this you can listen to the
 <a href="extension.html#type-Port">Port.onDisconnect</a>
 event. This event is fired either when the other side of the channel manually
 calls
 <a href="extension.html#type-Port">Port.disconnect()</a>, or when the page
 containing the port is unloaded (for example if the tab is navigated).
 onDisconnect is guaranteed to be fired only once for any given port.
 </p><h2 id="external">Cross-extension messaging</h2>
 <p>
 In addition to sending messages between different components in your
 extension, you can use the messaging API to communicate with other extensions.
 This lets you expose a public API that other extensions can take advantage of.
 </p><p>
 Listening for incoming requests and connections is similar to the internal
 case, except you use the
 <a href="extension.html#event-onRequestExternal">chrome.extension.onRequestExternal</a>
 or
 <a href="extension.html#event-onConnectExternal">chrome.extension.onConnectExternal</a>
 methods. Here's an example of each:
 </p><pre>// For simple requests:
 chrome.extension.onRequestExternal.addListener(
   function(request, sender, sendResponse) {
     if (sender.id == blacklistedExtension)
       return;  // don't allow this extension access
     else if (request.getTargetData)
       sendResponse({targetData: targetData});
     else if (request.activateLasers) {
       var success = activateLasers();
       sendResponse({activateLasers: success});
     }
   });
 // For long-lived connections:
 chrome.extension.onConnectExternal.addListener(function(port) {
   port.onMessage.addListener(function(msg) {
     // See other examples for sample onMessage handlers.
   });
 });
 </pre>
 <p>
 Likewise, sending a message to another extension is similar to sending one
 within your extension. The only difference is that you must pass the ID of the
 extension you want to communicate with. For example:
 </p><pre>// The ID of the extension we want to talk to.
 var laserExtensionId = "abcdefghijklmnoabcdefhijklmnoabc";
 // Make a simple request:
 chrome.extension.sendRequest(laserExtensionId, {getTargetData: true},
   function(response) {
     if (targetInRange(response.targetData))
       chrome.extension.sendRequest(laserExtensionId, {activateLasers: true});
   });
 // Start a long-running conversation:
 var port = chrome.extension.connect(laserExtensionId);
 port.postMessage(...);
 </pre>
 <h2 id="security-considerations">Security considerations</h2>
 <p>
 When receiving a message from a content script or another extension, your
 background page should be careful not to fall victim to <a href="http://en.wikipedia.org/wiki/Cross-site_scripting">cross-site
 scripting</a>.  Specifically, avoid using dangerous APIs such as the
 below:
 </p>
 <pre>background.html
 ===============
 chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
   // WARNING! Might be evaluating an evil script!
   var resp = eval("(" + response.farewell + ")");
 });
 background.html
 ===============
 chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
   // WARNING! Might be injecting a malicious script!
   document.getElementById("resp").innerHTML = response.farewell;
 });
 </pre>
 <p>
 Instead, prefer safer APIs that do not run scripts:
 </p>
 <pre>background.html
 ===============
 chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
   // JSON.parse does not evaluate the attacker's scripts.
   var resp = JSON.parse(response.farewell);
 });
 background.html
 ===============
 chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
   // innerText does not let the attacker inject HTML elements.
   document.getElementById("resp").innerText = response.farewell;
 });
 </pre>
 <h2 id="examples">Examples</h2>
 <p>
 You can find simple examples of communication via messages in the
 <a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/messaging/">examples/api/messaging</a>
 directory.
 Also see the
 <a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/howto/contentscript_xhr">contentscript_xhr</a> example,
 in which a content script and its parent extension exchange messages,
 so that the parent extension can perform
 cross-site requests on behalf of the content script.
 For more examples and for help in viewing the source code, see
 <a href="samples.html">Samples</a>.
 </p>
 </div>
         <!-- API PAGE -->
          <!-- /apiPage -->
       </div> <!-- /gc-pagecontent -->
     </div> <!-- /g-section -->
   </div> <!-- /codesiteContent -->
     <div id="gc-footer" --="">
       <div class="text">
   <p>
   Except as otherwise <a href="http://code.google.com/policies.html#restrictions">noted</a>,
   the content of this page is licensed under the <a rel="license" href="http://creativecommons.org/licenses/by/3.0/">Creative Commons
   Attribution 3.0 License</a>, and code samples are licensed under the
   <a rel="license" href="http://code.google.com/google_bsd_license.html">BSD License</a>.
   </p>
   <p>
   ©2011 Google
   </p>
 <!-- begin analytics -->
 <script src="https://www.google-analytics.com/urchin.js" type="text/javascript"></script>
 <script src="https://www.google-analytics.com/ga.js" type="text/javascript"></script>
 <script type="text/javascript">
   // chrome doc tracking
   try {
     var engdocs = _gat._getTracker("YT-10763712-2");
     engdocs._trackPageview();
   } catch(err) {}
   // code.google.com site-wide tracking
   try {
     _uacct="UA-18071-1";
     _uanchor=1;
     _uff=0;
     urchinTracker();
   }
   catch(e) {/* urchinTracker not available. */}
 </script>
 <!-- end analytics -->
       </div>
     </div> <!-- /gc-footer -->
   </div> <!-- /gc-container -->
 </body></html>
	<!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>Message Passing - 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">
	<!-- SUBTEMPLATES: DO NOT MOVE FROM THIS LOCATION -->
	<!-- 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" -->
	<!-- /SUBTEMPLATES -->
	<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>
	<!-- API HEADER -->
	<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> <!-- end gc-topnav -->
	<div class="g-section g-tpl-170">
	<!-- SIDENAV -->
	<div class="g-unit g-first" id="gc-toc">
	<ul>
	<li><a href="getstarted.html">Getting Started</a></li>
	<li><a href="overview.html">Overview</a></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 class="leftNavSelected">Message Passing</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">Message Passing</h1>
	</div>
	<!-- TABLE OF CONTENTS -->
	<div id="toc">
	<h2>Contents</h2>
	<ol>
	<li>
	<a href="#simple">Simple one-time requests</a>
	<ol>
	</ol>
	</li><li>
	<a href="#connect">Long-lived connections</a>
	<ol>
	</ol>
	</li><li>
	<a href="#external">Cross-extension messaging</a>
	<ol>
	</ol>
	</li><li>
	<a href="#security-considerations">Security considerations</a>
	<ol>
	</ol>
	</li><li>
	<a href="#examples">Examples</a>
	<ol>
	</ol>
	</li>
	</ol>
	</div>
	<!-- /TABLE OF CONTENTS -->
	<!-- Standard content lead-in for experimental API pages -->
	<!-- STATIC CONTENT PLACEHOLDER -->
	<div id="static"><div id="pageData-name" class="pageData">Message Passing</div>
	<div id="pageData-showTOC" class="pageData">true</div>
	<p>
	Since content scripts run in the context of a web page and not the extension,
	they often need some way of communicating with the rest of the extension. For
	example, an RSS reader extension might use content scripts to detect the
	presence of an RSS feed on a page, then notify the background page in order to
	display a page action icon for that page.
	</p><p>
	Communication between extensions and their content scripts works by using
	message passing. Either side can listen for messages sent from the other end,
	and respond on the same channel. A message can contain any valid JSON object
	(null, boolean, number, string, array, or object). There is a simple API for
	<a href="#simple">one-time requests</a>
	and a more complex API that allows you to have
	<a href="#connect">long-lived connections</a>
	for exchanging multiple messages with a shared context. It is also possible to
	send a message to another extension if you know its ID, which is covered in
	the
	<a href="#external">cross-extension messages</a>
	section.
	</p><h2 id="simple">Simple one-time requests</h2>
	<p>
	If you only need to send a single message to another part of your extension
	(and optionally get a response back), you should use the simplified
	<a href="extension.html#method-sendRequest">chrome.extension.sendRequest()</a>
	or
	<a href="tabs.html#method-sendRequest">chrome.tabs.sendRequest()</a>
	methods. This lets you send a one-time JSON-serializable message from a
	content script to extension, or vice versa, respectively. An optional
	callback parameter allows you handle the response from the other side, if
	there is one.
	</p><p>
	Sending a request from a content script looks like this:
	</p><pre>contentscript.js
	================
	chrome.extension.sendRequest({greeting: "hello"}, function(response) {
	console.log(response.farewell);
	});
	</pre>
	<p>
	Sending a request from the extension to a content script looks very similar,
	except that you need to specify which tab to send it to. This example
	demonstrates sending a message to the content script in the selected tab.
	</p><pre>background.html
	===============
	chrome.tabs.getSelected(null, function(tab) {
	chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
	console.log(response.farewell);
	});
	});
	</pre>
	<p>
	On the receiving end, you need to set up an
	<a href="extension.html#event-onRequest">chrome.extension.onRequest</a>
	event listener to handle the message. This looks the same from a content
	script or extension page.
	</p><pre>chrome.extension.onRequest.addListener(
	function(request, sender, sendResponse) {
	console.log(sender.tab ?
	"from a content script:" + sender.tab.url :
	"from the extension");
	if (request.greeting == "hello")
	sendResponse({farewell: "goodbye"});
	});
	</pre>
	<p class="note">
	<b>Note:</b> If multiple pages are listening for onRequest events, only the
	first to call sendResponse() for a particular event will succeed in sending the
	response. All other responses to that event will be ignored.
	</p>
	<h2 id="connect">Long-lived connections</h2>
	<p>
	Sometimes it's useful to have a conversation that lasts longer than a single
	request and response. In this case, you can open a long-lived channel from
	your content script to an extension page, or vice versa, using
	<a href="extension.html#method-connect">chrome.extension.connect()</a>
	or
	<a href="tabs.html#method-connect">chrome.tabs.connect()</a> respectively. The
	channel can optionally have a name, allowing you to distinguish between
	different types of connections.
	</p><p>
	One use case might be an automatic form fill extension. The content script
	could open a channel to the extension page for a particular login, and send a
	message to the extension for each input element on the page to request the
	form data to fill in. The shared connection allows the extension to keep
	shared state linking the several messages coming from the content script.
	</p><p>
	When establishing a connection, each end is given a
	<a href="extension.html#type-Port">Port</a>
	object which is used for sending and receiving messages through that
	connection.
	</p><p>
	Here is how you open a channel from a content script, and send and listen for
	messages:
	</p><pre>contentscript.js
	================
	var port = chrome.extension.connect({name: "knockknock"});
	port.postMessage({joke: "Knock knock"});
	port.onMessage.addListener(function(msg) {
	if (msg.question == "Who's there?")
	port.postMessage({answer: "Madame"});
	else if (msg.question == "Madame who?")
	port.postMessage({answer: "Madame... Bovary"});
	});
	</pre>
	<p>
	Sending a request from the extension to a content script looks very similar,
	except that you need to specify which tab to connect to. Simply replace the
	call to connect in the above example with
	<a href="tabs.html#method-connect">chrome.tabs.connect(tabId, {name:
	"knockknock"})</a>.
	</p><p>
	In order to handle incoming connections, you need to set up a
	<a href="extension.html#event-onConnect">chrome.extension.onConnect</a>
	event listener. This looks the same from a content script or an extension
	page. When another part of your extension calls "connect()", this event is
	fired, along with the
	<a href="extension.html#type-Port">Port</a>
	object you can use to send and receive messages through the connection. Here's
	what it looks like to respond to incoming connections:
	</p><pre>chrome.extension.onConnect.addListener(function(port) {
	console.assert(port.name == "knockknock");
	port.onMessage.addListener(function(msg) {
	if (msg.joke == "Knock knock")
	port.postMessage({question: "Who's there?"});
	else if (msg.answer == "Madame")
	port.postMessage({question: "Madame who?"});
	else if (msg.answer == "Madame... Bovary")
	port.postMessage({question: "I don't get it."});
	});
	});
	</pre>
	<p>
	You may want to find out when a connection is closed, for example if you are
	maintaining separate state for each open port. For this you can listen to the
	<a href="extension.html#type-Port">Port.onDisconnect</a>
	event. This event is fired either when the other side of the channel manually
	calls
	<a href="extension.html#type-Port">Port.disconnect()</a>, or when the page
	containing the port is unloaded (for example if the tab is navigated).
	onDisconnect is guaranteed to be fired only once for any given port.
	</p><h2 id="external">Cross-extension messaging</h2>
	<p>
	In addition to sending messages between different components in your
	extension, you can use the messaging API to communicate with other extensions.
	This lets you expose a public API that other extensions can take advantage of.
	</p><p>
	Listening for incoming requests and connections is similar to the internal
	case, except you use the
	<a href="extension.html#event-onRequestExternal">chrome.extension.onRequestExternal</a>
	or
	<a href="extension.html#event-onConnectExternal">chrome.extension.onConnectExternal</a>
	methods. Here's an example of each:
	</p><pre>// For simple requests:
	chrome.extension.onRequestExternal.addListener(
	function(request, sender, sendResponse) {
	if (sender.id == blacklistedExtension)
	return; // don't allow this extension access
	else if (request.getTargetData)
	sendResponse({targetData: targetData});
	else if (request.activateLasers) {
	var success = activateLasers();
	sendResponse({activateLasers: success});
	}
	});
	// For long-lived connections:
	chrome.extension.onConnectExternal.addListener(function(port) {
	port.onMessage.addListener(function(msg) {
	// See other examples for sample onMessage handlers.
	});
	});
	</pre>
	<p>
	Likewise, sending a message to another extension is similar to sending one
	within your extension. The only difference is that you must pass the ID of the
	extension you want to communicate with. For example:
	</p><pre>// The ID of the extension we want to talk to.
	var laserExtensionId = "abcdefghijklmnoabcdefhijklmnoabc";
	// Make a simple request:
	chrome.extension.sendRequest(laserExtensionId, {getTargetData: true},
	function(response) {
	if (targetInRange(response.targetData))
	chrome.extension.sendRequest(laserExtensionId, {activateLasers: true});
	});
	// Start a long-running conversation:
	var port = chrome.extension.connect(laserExtensionId);
	port.postMessage(...);
	</pre>
	<h2 id="security-considerations">Security considerations</h2>
	<p>
	When receiving a message from a content script or another extension, your
	background page should be careful not to fall victim to <a href="http://en.wikipedia.org/wiki/Cross-site_scripting">cross-site
	scripting</a>. Specifically, avoid using dangerous APIs such as the
	below:
	</p>
	<pre>background.html
	===============
	chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
	// WARNING! Might be evaluating an evil script!
	var resp = eval("(" + response.farewell + ")");
	});
	background.html
	===============
	chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
	// WARNING! Might be injecting a malicious script!
	document.getElementById("resp").innerHTML = response.farewell;
	});
	</pre>
	<p>
	Instead, prefer safer APIs that do not run scripts:
	</p>
	<pre>background.html
	===============
	chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
	// JSON.parse does not evaluate the attacker's scripts.
	var resp = JSON.parse(response.farewell);
	});
	background.html
	===============
	chrome.tabs.sendRequest(tab.id, {greeting: "hello"}, function(response) {
	// innerText does not let the attacker inject HTML elements.
	document.getElementById("resp").innerText = response.farewell;
	});
	</pre>
	<h2 id="examples">Examples</h2>
	<p>
	You can find simple examples of communication via messages in the
	<a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/messaging/">examples/api/messaging</a>
	directory.
	Also see the
	<a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/howto/contentscript_xhr">contentscript_xhr</a> example,
	in which a content script and its parent extension exchange messages,
	so that the parent extension can perform
	cross-site requests on behalf of the content script.
	For more examples and for help in viewing the source code, see
	<a href="samples.html">Samples</a>.
	</p>
	</div>
	<!-- API PAGE -->
	<!-- /apiPage -->
	</div> <!-- /gc-pagecontent -->
	</div> <!-- /g-section -->
	</div> <!-- /codesiteContent -->
	<div id="gc-footer" --="">
	<div class="text">
	<p>
	Except as otherwise <a href="http://code.google.com/policies.html#restrictions">noted</a>,
	the content of this page is licensed under the <a rel="license" href="http://creativecommons.org/licenses/by/3.0/">Creative Commons
	Attribution 3.0 License</a>, and code samples are licensed under the
	<a rel="license" href="http://code.google.com/google_bsd_license.html">BSD License</a>.
	</p>
	<p>
	©2011 Google
	</p>
	<!-- begin analytics -->
	<script src="https://www.google-analytics.com/urchin.js" type="text/javascript"></script>
	<script src="https://www.google-analytics.com/ga.js" type="text/javascript"></script>
	<script type="text/javascript">
	// chrome doc tracking
	try {
	var engdocs = _gat._getTracker("YT-10763712-2");
	engdocs._trackPageview();
	} catch(err) {}
	// code.google.com site-wide tracking
	try {
	_uacct="UA-18071-1";
	_uanchor=1;
	_uff=0;
	urchinTracker();
	}
	catch(e) {/* urchinTracker not available. */}
	</script>
	<!-- end analytics -->
	</div>
	</div> <!-- /gc-footer -->
	</div> <!-- /gc-container -->
	</body></html>