1 <div id="pageData-name" class="pageData">Background Pages</div> 2 <div id="pageData-showTOC" class="pageData">true</div> 3 4 <p> 5 A common need for extensions is to have 6 a single long-running script to manage some task or state. 7 Background pages to the rescue. 8 </p> 9 10 <p> 11 As the <a href="overview.html#arch">architecture overview</a> explains, 12 the background page is an HTML page that runs in the extension process. 13 It exists for the lifetime of your extension, 14 and only one instance of it at a time is active. 15 </p> 16 17 <p> 18 In a typical extension with a background page, 19 the UI — 20 for example, the browser action or page action 21 and any options page — 22 is implemented by dumb views. 23 When the view needs some state, 24 it requests the state from the background page. 25 When the background page notices a state change, 26 the background page tells the views to update. 27 </p> 28 29 <h2 id="manifest">Manifest</h2> 30 31 <p> 32 Register your background page in the 33 <a href="manifest.html">extension manifest</a> 34 like this: 35 </p> 36 37 <pre>{ 38 "name": "My extension", 39 ... 40 <b>"background_page": "background.html"</b>, 41 ... 42 }</pre> 43 44 <p> 45 If you need the browser to start up early—so 46 you can display notifications, for example—then 47 you might also want to specify the 48 <a href="manifest.html#permissions">"background" permission</a>. 49 </p> 50 51 52 <h2>Details</h2> 53 54 <p> 55 You can communicate between your various pages using direct script calls, 56 similar to how frames can communicate. 57 The <a href="extension.html#method-getViews"><code>chrome.extension.getViews()</code></a> method 58 returns a list of window objects 59 for every active page belonging to your extension, 60 and the 61 <a href="extension.html#method-getBackgroundPage"><code>chrome.extension.getBackgroundPage()</code></a> method 62 returns the background page. 63 </p> 64 65 <h2 id="example">Example</h2> 66 67 <p> 68 The following code snippet demonstrates 69 how the background page 70 can interact with other pages in the extension. 71 It also shows how you can use 72 the background page to handle events 73 such as user clicks. 74 </p> 75 76 <p> 77 The extension in this example 78 has a background page 79 and multiple pages created 80 (with 81 <a href="tabs.html#method-create"><code>chrome.tabs.create()</code></a>) 82 from a file named <code>image.html</code>. 83 <!-- [PENDING: Once we have our set of samples, we should point to the example this is from and to other relevant examples. This is currently untested code derived from the screenshot sample.] --> 84 </p> 85 86 <pre> 87 <em>//In the background page:</em> 88 <html> 89 <script> 90 //React when a browser action's icon is clicked. 91 chrome.browserAction.onClicked.addListener(function(tab) { 92 var viewTabUrl = chrome.extension.getURL('image.html'); 93 var imageUrl = <em>/* an image's URL */</em>; 94 95 //Look through all the pages in this extension to find one we can use. 96 var views = chrome.extension.getViews(); 97 for (var i = 0; i < views.length; i++) { 98 var view = views[i]; 99 100 //If this view has the right URL and hasn't been used yet... 101 if (view.location.href == viewTabUrl && !view.imageAlreadySet) { 102 103 //...call one of its functions and set a property. 104 view.setImageUrl(imageUrl); 105 view.imageAlreadySet = true; 106 break; //we're done 107 } 108 } 109 }); 110 </script> 111 </html> 112 113 <em>//In image.html:</em> 114 <html> 115 <script> 116 function setImageUrl(url) { 117 document.getElementById('target').src = url; 118 } 119 </script> 120 121 <body> 122 <p> 123 Image here: 124 </p> 125 126 <img id="target" src="white.png" width="640" height="480"> 127 128 </body> 129 </html> 130 </pre> 131 132
