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(简体)</span></a></li><li class=" "><a data-locale="zh-TW" href="/zh-TW/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background" class="button submenu-item"><span>正體中文 (繁體)</span></a></li></ul></div></div></li></ul></div></div></div></div><div class="main-wrapper"><div class="sidebar-container"><aside id="sidebar-quicklinks" class="sidebar" data-macro="AddonSidebar"><button type="button" class="button action backdrop" aria-label="Collapse sidebar"><span class="button-wrap"></span></button><nav aria-label="Related Topics" class="sidebar-inner"><header class="sidebar-actions"><section class="sidebar-filter-container"><div class="sidebar-filter "><label id="sidebar-filter-label" class="sidebar-filter-label" for="sidebar-filter-input"><span class="icon icon-filter"></span><span class="visually-hidden">Filter sidebar</span></label><input id="sidebar-filter-input" autoComplete="off" class="sidebar-filter-input-field false" type="text" placeholder="Filter" value=""/><button type="button" class="button action has-icon clear-sidebar-filter-button"><span class="button-wrap"><span class="icon icon-cancel "></span><span class="visually-hidden">Clear filter input</span></span></button></div></section></header><div class="sidebar-inner-nav"><div class="in-nav-toc"><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#browser_support">Browser support</a></li><li class="document-toc-item "><a class="document-toc-link" href="#examples">Examples</a></li><li class="document-toc-item "><a class="document-toc-link" href="#browser_compatibility">Browser compatibility</a></li></ul></section></div></div><div class="sidebar-body"> <ol> <li class="section"><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions">Browser extensions</a></li> <li> <details> <summary>Getting started</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions">What are extensions?</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension">Your first extension</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_second_WebExtension">Your second extension</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Anatomy_of_a_WebExtension">Anatomy of an extension</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Examples">Example extensions</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_next">What next?</a></li> </ol> </details> </li> <li> <details> <summary>Concepts</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API">JavaScript APIs</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_scripts">Content scripts</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Background_scripts">Background scripts</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Match_patterns">Match patterns</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Working_with_files">Work with files</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Internationalization">Internationalization</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_Security_Policy">Content Security Policy</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Native_messaging">Native messaging</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Differences_between_API_implementations">Differences between API implementations</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Chrome_incompatibilities">Chrome incompatibilities</a></li> </ol> </details> </li> <li> <details> <summary>User interface</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface">User interface</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Toolbar_button">Toolbar button</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Page_actions">Address bar button</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Sidebars">Sidebars</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Context_menu_items">Context menu items</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Options_pages">Options page</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Extension_pages">Extension pages</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Notifications">Notifications</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Omnibox">Address bar suggestions</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/devtools_panels">devtools panels</a></li> </ol> </details> </li> <li> <details> <summary>How to</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Intercept_HTTP_requests">Intercept HTTP requests</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Modify_a_web_page">Modify a web page</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Safely_inserting_external_content_into_a_page">Insert external content</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Sharing_objects_with_page_scripts">Share objects with page scripts</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Add_a_button_to_the_toolbar">Add a button to the toolbar</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Implement_a_settings_page">Implement a settings page</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Working_with_the_Tabs_API">Work with the Tabs API</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_the_Bookmarks_API">Work with the Bookmarks API</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_the_Cookies_API">Work with the Cookies API</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_contextual_identities">Work with contextual identities</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Interact_with_the_clipboard">Interact with the clipboard</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Extending_the_developer_tools">Extend the developer tools</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Build_a_cross_browser_extension">Build a cross-browser extension</a></li> </ol> </details> </li> <li> <details> <summary>JavaScript APIs</summary> <ol><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Browser_support_for_JavaScript_APIs">Browser support for JavaScript APIs</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/action">action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/alarms">alarms</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/bookmarks">bookmarks</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browserAction">browserAction</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browserSettings">browserSettings</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browsingData">browsingData</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/captivePortal">captivePortal</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/clipboard">clipboard</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/commands">commands</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contentScripts">contentScripts</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contextualIdentities">contextualIdentities</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/cookies">cookies</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/declarativeNetRequest">declarativeNetRequest</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/devtools">devtools</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dns">dns</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dom">dom</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/downloads">downloads</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/events">events</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/extension">extension</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/extensionTypes">extensionTypes</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/find">find</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/history">history</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/i18n">i18n</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/identity">identity</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/idle">idle</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/management">management</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/menus">menus</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/notifications">notifications</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/omnibox">omnibox</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/pageAction">pageAction</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/permissions">permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/pkcs11">pkcs11</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/privacy">privacy</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/proxy">proxy</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime">runtime</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting">scripting</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/search">search</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/sessions">sessions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/sidebarAction">sidebarAction</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage">storage</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/tabs">tabs</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/theme">theme</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/topSites">topSites</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/types">types</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/userScripts">userScripts</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webNavigation">webNavigation</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest">webRequest</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/windows">windows</a></li></ol> </details> </li> <li> <details open=""> <summary>Manifest keys</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json">manifest.json</a></li> </ol> <ol><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/action">action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/author">author</a></li><li><em><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background" aria-current="page">background</a></em></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/browser_action">browser_action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/browser_specific_settings">browser_specific_settings</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/chrome_settings_overrides">chrome_settings_overrides</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/chrome_url_overrides">chrome_url_overrides</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/commands">commands</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_scripts">content_scripts</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy">content_security_policy</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/declarative_net_request">declarative_net_request</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/default_locale">default_locale</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/description">description</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/developer">developer</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/devtools_page">devtools_page</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/dictionaries">dictionaries</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/externally_connectable">externally_connectable</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/homepage_url">homepage_url</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/host_permissions">host_permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/icons">icons</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/incognito">incognito</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/manifest_version">manifest_version</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/name">name</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/offline_enabled">offline_enabled</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/omnibox">omnibox</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/optional_host_permissions">optional_host_permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/optional_permissions">optional_permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/options_page">options_page</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/options_ui">options_ui</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/page_action">page_action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/permissions">permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/protocol_handlers">protocol_handlers</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/short_name">short_name</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sidebar_action">sidebar_action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/storage">storage</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme">theme</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme_experiment">theme_experiment</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/user_scripts">user_scripts</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/version">version</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/version_name">version_name</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/web_accessible_resources">web_accessible_resources</a></li></ol> </details> </li> <li> <details> <summary>Extension Workshop</summary> <ol> <li><a href="https://extensionworkshop.com/documentation/develop/">Develop</a></li> <li><a href="https://extensionworkshop.com/documentation/publish/">Publish</a></li> <li><a href="https://extensionworkshop.com/documentation/manage/">Manage</a></li> <li><a href="https://extensionworkshop.com/documentation/enterprise/">Enterprise</a></li> </ol> </details> </li> <li class="section"><a href="/en-US/docs/Mozilla/Add-ons/Contact_us">Contact us</a></li> <li> <details> <summary>Channels</summary> <ol> <li><a href="https://blog.mozilla.org/addons">Add-ons blog</a></li> <li><a href="https://discourse.mozilla.org/c/add-ons">Add-ons forum</a></li> <li><a href="https://chat.mozilla.org/#/room/%23addons:mozilla.org">Add-ons chat</a></li> </ol> </details> </li> </ol> </div></div><section class="place side"></section></nav></aside><div class="toc-container"><aside class="toc"><nav><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#browser_support">Browser support</a></li><li class="document-toc-item "><a class="document-toc-link" href="#examples">Examples</a></li><li class="document-toc-item "><a class="document-toc-link" href="#browser_compatibility">Browser compatibility</a></li></ul></section></div></nav></aside><section class="place side"></section></div></div><main id="content" class="main-content "><article class="main-page-content" lang="en-US"><header><h1>background</h1></header><div class="section-content"><figure class="table-container"><table class="fullwidth-table standard-table"> <tbody> <tr> <th scope="row">Type</th> <td><code>Object</code></td> </tr> <tr> <th scope="row">Mandatory</th> <td>No</td> </tr> <tr> <th scope="row">Manifest version</th> <td>2 or higher</td> </tr> <tr> <th scope="row">Example</th> <td> <div class="code-example"><div class="example-header"><span class="language-name">json</span></div><pre class="brush: json notranslate"><code>"background": { "scripts": ["background.js"] }</code></pre></div> </td> </tr> </tbody> </table></figure> <p>Use the <code>background</code> key to include one or more background scripts, a background page, or a Service worker in your extension.</p> <p>Background scripts are the place to put code that needs to maintain a long-term state or perform long-term operations independently of the lifetime of any particular web pages or browser windows.</p> <p>Background scripts are loaded as soon as the extension is loaded and stay loaded until the extension is disabled or uninstalled unless <code>persistent</code> is specified as <code>false</code>. You can use any WebExtension APIs in the script if you have requested the necessary <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/permissions">permissions</a>.</p> <p>See <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Background_scripts">Background scripts</a> for some more details.</p> <p>The <code>background</code> key is an object that must have one of these properties (for more information on how these properties are supported, see <a href="#browser_support">Browser support</a>):</p> <figure class="table-container"><table class="standard-table"> <tbody> <tr> <td><code>page</code></td> <td> <p> If you need specific content in the background page, you can define a page using the <code>page</code> property. This is a <code>String</code> representing a path relative to the manifest.json file to an HTML document included in your extension bundle. </p> <p> If you use this property, you can not specify background scripts using <code>scripts</code>, but you can include scripts from the page, just like a normal web page. </p> </td> </tr> <tr> <td><code>scripts</code></td> <td> <p> An <code>Array</code> of <code>Strings</code>, each of which is a path to a JavaScript source. The path is relative to the manifest.json file itself. These are the scripts that are executed in the extension's background page. </p> <p>The scripts share the same <code>window</code> global context.</p> <p>The scripts are loaded in the order they appear in the array.</p> <p> If you specify <code>scripts</code>, an empty page is created where your scripts run. </p> <div class="note notecard"> <p> <strong>Note:</strong> If you want to fetch a script from a remote location with the <code><script></code> tag (e.g., <code><script src = "https://code.jquery.com/jquery-3.6.0.min.js"></code>), you have to change the <code><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy">content_security_policy</a></code> key in the manifest.json file of your extension. </p> </div> </td> </tr> <tr> <td><code>service_worker</code></td> <td> <p>Specify a JavaScript file as the extension <a href="/en-US/docs/Web/API/Service_Worker_API">service worker</a>. A service worker is a background script that acts as the extension's main event handler.</p> </td> </tr> </tbody> </table></figure> <p>The <code>background</code> key can also contain this optional property:</p> <figure class="table-container"><table class="standard-table"> <tbody> <tr> <td><code>persistent</code></td> <td> <p>A <code>Boolean</code> value.</p> <p>If omitted, this property defaults to <code>true</code> in Manifest V2 and <code>false</code> in Manifest V3. Setting to <code>true</code> in Manifest V3 results in an error.</p> <ul> <li> <code>true</code> indicates the background page is to be kept in memory from when the extension is loaded or the browser starts until the extension is unloaded or disabled, or the browser is closed (that is, the background page is persistent). </li> <li> <code>false</code> indicates the background page may be unloaded from memory when idle and recreated when needed. Such background pages are often called Event Pages, because they are loaded into memory to allow the background page to handle the events to which it has added listeners. Registration of listeners is persistent when the page is unloaded from memory, but other values are not persistent. If you want to store data persistently in an event page, then you should use the <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage">storage API</a>. </li> </ul> </td> </tr> <tr> <td><code>type</code></td> <td> <p>A <code>String</code> value.</p> <p>Determines whether the scripts specified in <code>"scripts"</code> are loaded as ES modules.</p> <ul> <li><code>classic</code> indicates the background scripts or service workers are not included as an ES Module.</li> <li><code>module</code> indicates the background scripts or service workers are included as an ES Module. This enables the background page or service worker to <code>import</code> code.</li> </ul> <p>If omitted, this property defaults to <code>classic</code>.</p> </td> </tr> </tbody> </table></figure></div><section aria-labelledby="browser_support"><h2 id="browser_support"><a href="#browser_support">Browser support</a></h2><div class="section-content"><p>Support for the <code>scripts</code>, <code>page</code>, and <code>service_worker</code> properties varies between browsers like this:</p> <ul> <li>Chrome: <ul> <li>supports <code>background.service_worker</code>.</li> <li>supports <code>background.scripts</code> (and <code>background.page</code>) in Manifest V2 extensions only.</li> <li>before Chrome 121, Chrome refuses to load a Manifest V3 extension with <code>background.scripts</code> or <code>background.page</code> present. From Chrome 121, their presence in a Manifest V3 extension is ignored.</li> </ul> </li> <li>Firefox: <ul> <li><code>background.service_worker</code> is not supported (see <a href="https://bugzil.la/1573659" class="external" target="_blank">Firefox bug 1573659</a>).</li> <li>supports <code>background.scripts</code> (or <code>background.page</code>) if <code>service_worker</code> is not specified or the service worker feature is disabled. Before Firefox 120, Firefox did not start the background page if <code>service_worker</code> was present (see <a href="https://bugzil.la/1860304" class="external" target="_blank">Firefox bug 1860304</a>). From Firefox 121, the background page starts as expected, regardless of the presence of <code>service_worker</code>.</li> </ul> </li> <li>Safari: <ul> <li>supports <code>background.service_worker</code>.</li> <li>supports <code>background.scripts</code> (or <code>background.page</code>) if <code>service_worker</code> is not specified.</li> </ul> </li> </ul> <p>To illustrate, this is an example of a cross-browser extension that supports <code>scripts</code> and <code>service_worker</code>. The example has this manifest.json file:</p> <div class="code-example"><div class="example-header"><span class="language-name">json</span></div><pre class="brush: json notranslate"><code>{ "name": "Demo of service worker + event page", "version": "1", "manifest_version": 3, "background": { "scripts": ["background.js"], "service_worker": "background.js" } } </code></pre></div> <p>And, background.js contains:</p> <div class="code-example"><div class="example-header"><span class="language-name">javascript</span></div><pre class="brush: javascript notranslate"><code>if (typeof browser == "undefined") { // Chrome does not support the browser namespace yet. globalThis.browser = chrome; } browser.runtime.onInstalled.addListener(() => { browser.tabs.create({ url: "http://example.com/first-run.html" }); }); </code></pre></div> <p>When the extension is executed, this happens:</p> <ul> <li>in Chrome, the <code>service_worker</code> property is used, and a service worker starts that opens the tab because, in a Manifest V3 extension, Chrome only supports service workers for background scripts.</li> <li>in Firefox, the <code>scripts</code> property is used, and a script starts that opens the tab because Firefox only supports scripts for background scripts.</li> <li>in Safari, the <code>service_worker</code> property is used, and a service worker starts that opens the tab because Safari gives priority to using service workers for background scripts.</li> </ul></div></section><section aria-labelledby="examples"><h2 id="examples"><a href="#examples">Examples</a></h2><div class="section-content"><div class="code-example"><div class="example-header"><span class="language-name">json</span></div><pre class="brush: json notranslate"><code> "background": { "scripts": ["jquery.js", "my-background.js"] } </code></pre></div> <p>Load two background scripts.</p> <div class="code-example"><div class="example-header"><span class="language-name">json</span></div><pre class="brush: json notranslate"><code> "background": { "page": "my-background.html" } </code></pre></div> <p>Load a custom background page.</p></div></section><h2 id="browser_compatibility"><a href="#browser_compatibility">Browser compatibility</a></h2><p>BCD tables only load in the browser<noscript> with JavaScript enabled. 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Content available under <a href="/en-US/docs/MDN/Writing_guidelines/Attrib_copyright_license">a Creative Commons license</a>.</p></div></div></footer></div><script type="application/json" id="hydration">{"url":"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background","doc":{"isMarkdown":true,"isTranslated":false,"isActive":true,"flaws":{},"title":"background","mdn_url":"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background","locale":"en-US","native":"English (US)","browserCompat":["webextensions.manifest.background"],"sidebarHTML":"\n <ol>\n <li class=\"section\"><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions\">Browser extensions</a></li>\n <li>\n <details>\n <summary>Getting started</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions\">What are extensions?</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension\">Your first extension</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_second_WebExtension\">Your second extension</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Anatomy_of_a_WebExtension\">Anatomy of an extension</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Examples\">Example extensions</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_next\">What next?</a></li>\n </ol>\n </details>\n </li>\n <li>\n <details>\n <summary>Concepts</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API\">JavaScript APIs</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_scripts\">Content scripts</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Background_scripts\">Background scripts</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Match_patterns\">Match patterns</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Working_with_files\">Work with files</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Internationalization\">Internationalization</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_Security_Policy\">Content Security Policy</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Native_messaging\">Native messaging</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Differences_between_API_implementations\">Differences between API implementations</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Chrome_incompatibilities\">Chrome incompatibilities</a></li>\n </ol>\n </details>\n </li>\n <li>\n <details>\n <summary>User interface</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface\">User interface</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Toolbar_button\">Toolbar button</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Page_actions\">Address bar button</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Sidebars\">Sidebars</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Context_menu_items\">Context menu items</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Options_pages\">Options page</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Extension_pages\">Extension pages</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Notifications\">Notifications</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Omnibox\">Address bar suggestions</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/devtools_panels\">devtools panels</a></li>\n </ol>\n </details>\n </li>\n <li>\n <details>\n <summary>How to</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Intercept_HTTP_requests\">Intercept HTTP requests</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Modify_a_web_page\">Modify a web page</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Safely_inserting_external_content_into_a_page\">Insert external content</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Sharing_objects_with_page_scripts\">Share objects with page scripts</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Add_a_button_to_the_toolbar\">Add a button to the toolbar</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Implement_a_settings_page\">Implement a settings page</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Working_with_the_Tabs_API\">Work with the Tabs API</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_the_Bookmarks_API\">Work with the Bookmarks API</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_the_Cookies_API\">Work with the Cookies API</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_contextual_identities\">Work with contextual identities</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Interact_with_the_clipboard\">Interact with the clipboard</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Extending_the_developer_tools\">Extend the developer tools</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Build_a_cross_browser_extension\">Build a cross-browser extension</a></li>\n </ol>\n </details>\n </li>\n <li>\n <details>\n <summary>JavaScript APIs</summary>\n <ol><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Browser_support_for_JavaScript_APIs\">Browser support for JavaScript APIs</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/action\">action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/alarms\">alarms</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/bookmarks\">bookmarks</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browserAction\">browserAction</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browserSettings\">browserSettings</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browsingData\">browsingData</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/captivePortal\">captivePortal</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/clipboard\">clipboard</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/commands\">commands</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contentScripts\">contentScripts</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contextualIdentities\">contextualIdentities</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/cookies\">cookies</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/declarativeNetRequest\">declarativeNetRequest</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/devtools\">devtools</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dns\">dns</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dom\">dom</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/downloads\">downloads</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/events\">events</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/extension\">extension</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/extensionTypes\">extensionTypes</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/find\">find</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/history\">history</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/i18n\">i18n</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/identity\">identity</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/idle\">idle</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/management\">management</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/menus\">menus</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/notifications\">notifications</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/omnibox\">omnibox</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/pageAction\">pageAction</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/permissions\">permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/pkcs11\">pkcs11</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/privacy\">privacy</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/proxy\">proxy</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime\">runtime</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting\">scripting</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/search\">search</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/sessions\">sessions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/sidebarAction\">sidebarAction</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage\">storage</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/tabs\">tabs</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/theme\">theme</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/topSites\">topSites</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/types\">types</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/userScripts\">userScripts</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webNavigation\">webNavigation</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest\">webRequest</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/windows\">windows</a></li></ol>\n </details>\n </li>\n <li>\n <details open=\"\">\n <summary>Manifest keys</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json\">manifest.json</a></li>\n </ol>\n <ol><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/action\">action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/author\">author</a></li><li><em><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background\" aria-current=\"page\">background</a></em></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/browser_action\">browser_action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/browser_specific_settings\">browser_specific_settings</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/chrome_settings_overrides\">chrome_settings_overrides</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/chrome_url_overrides\">chrome_url_overrides</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/commands\">commands</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_scripts\">content_scripts</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy\">content_security_policy</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/declarative_net_request\">declarative_net_request</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/default_locale\">default_locale</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/description\">description</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/developer\">developer</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/devtools_page\">devtools_page</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/dictionaries\">dictionaries</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/externally_connectable\">externally_connectable</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/homepage_url\">homepage_url</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/host_permissions\">host_permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/icons\">icons</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/incognito\">incognito</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/manifest_version\">manifest_version</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/name\">name</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/offline_enabled\">offline_enabled</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/omnibox\">omnibox</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/optional_host_permissions\">optional_host_permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/optional_permissions\">optional_permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/options_page\">options_page</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/options_ui\">options_ui</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/page_action\">page_action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/permissions\">permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/protocol_handlers\">protocol_handlers</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/short_name\">short_name</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sidebar_action\">sidebar_action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/storage\">storage</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme\">theme</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme_experiment\">theme_experiment</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/user_scripts\">user_scripts</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/version\">version</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/version_name\">version_name</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/web_accessible_resources\">web_accessible_resources</a></li></ol>\n </details>\n </li>\n <li>\n <details>\n <summary>Extension Workshop</summary>\n <ol>\n <li><a href=\"https://extensionworkshop.com/documentation/develop/\">Develop</a></li>\n <li><a href=\"https://extensionworkshop.com/documentation/publish/\">Publish</a></li>\n <li><a href=\"https://extensionworkshop.com/documentation/manage/\">Manage</a></li>\n <li><a href=\"https://extensionworkshop.com/documentation/enterprise/\">Enterprise</a></li>\n </ol>\n </details>\n </li>\n <li class=\"section\"><a href=\"/en-US/docs/Mozilla/Add-ons/Contact_us\">Contact us</a></li>\n <li>\n <details>\n <summary>Channels</summary>\n <ol>\n <li><a href=\"https://blog.mozilla.org/addons\">Add-ons blog</a></li>\n <li><a href=\"https://discourse.mozilla.org/c/add-ons\">Add-ons forum</a></li>\n <li><a href=\"https://chat.mozilla.org/#/room/%23addons:mozilla.org\">Add-ons chat</a></li>\n </ol>\n </details>\n </li>\n </ol>\n","sidebarMacro":"AddonSidebar","body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<figure class=\"table-container\"><table class=\"fullwidth-table standard-table\">\n <tbody>\n <tr>\n <th scope=\"row\">Type</th>\n <td><code>Object</code></td>\n </tr>\n <tr>\n <th scope=\"row\">Mandatory</th>\n <td>No</td>\n </tr>\n <tr>\n <th scope=\"row\">Manifest version</th>\n <td>2 or higher</td>\n </tr>\n <tr>\n <th scope=\"row\">Example</th>\n <td>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">json</span></div><pre class=\"brush: json notranslate\"><code>\"background\": {\n \"scripts\": [\"background.js\"]\n}</code></pre></div>\n </td>\n </tr>\n </tbody>\n</table></figure>\n<p>Use the <code>background</code> key to include one or more background scripts, a background page, or a Service worker in your extension.</p>\n<p>Background scripts are the place to put code that needs to maintain a long-term state or perform long-term operations independently of the lifetime of any particular web pages or browser windows.</p>\n<p>Background scripts are loaded as soon as the extension is loaded and stay loaded until the extension is disabled or uninstalled unless <code>persistent</code> is specified as <code>false</code>. You can use any WebExtension APIs in the script if you have requested the necessary <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/permissions\">permissions</a>.</p>\n<p>See <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Background_scripts\">Background scripts</a> for some more details.</p>\n<p>The <code>background</code> key is an object that must have one of these properties (for more information on how these properties are supported, see <a href=\"#browser_support\">Browser support</a>):</p>\n<figure class=\"table-container\"><table class=\"standard-table\">\n <tbody>\n <tr>\n <td><code>page</code></td>\n <td>\n <p>\n If you need specific content in the background page, you can define a\n page using the <code>page</code> property. This is a\n <code>String</code> representing a path relative to the manifest.json\n file to an HTML document included in your extension bundle.\n </p>\n <p>\n If you use this property, you can not specify background scripts using\n <code>scripts</code>, but you can include scripts from the\n page, just like a normal web page.\n </p>\n </td>\n </tr>\n <tr>\n <td><code>scripts</code></td>\n <td>\n <p>\n An <code>Array</code> of <code>Strings</code>, each of which is a path\n to a JavaScript source. The path is relative to the manifest.json file\n itself. These are the scripts that are executed in the\n extension's background page.\n </p>\n <p>The scripts share the same <code>window</code> global context.</p>\n <p>The scripts are loaded in the order they appear in the array.</p>\n <p>\n If you specify <code>scripts</code>, an empty page\n is created where your scripts run.\n </p>\n <div class=\"note notecard\">\n <p>\n <strong>Note:</strong> If you want to fetch a script from a remote\n location with the <code><script></code> tag (e.g.,\n <code><script src =\n\"https://code.jquery.com/jquery-3.6.0.min.js\"></code>), you have to change the\n <code><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy\">content_security_policy</a></code>\n key in the manifest.json file of your extension.\n </p>\n </div>\n </td>\n </tr>\n <tr>\n <td><code>service_worker</code></td>\n <td>\n <p>Specify a JavaScript file as the extension <a href=\"/en-US/docs/Web/API/Service_Worker_API\">service worker</a>. A service worker is a background script that acts as the extension's main event handler.</p>\n </td>\n </tr>\n </tbody>\n</table></figure>\n<p>The <code>background</code> key can also contain this optional property:</p>\n<figure class=\"table-container\"><table class=\"standard-table\">\n <tbody>\n <tr>\n <td><code>persistent</code></td>\n <td>\n <p>A <code>Boolean</code> value.</p>\n <p>If omitted, this property defaults to <code>true</code> in Manifest V2 and <code>false</code> in Manifest V3. Setting to <code>true</code> in Manifest V3 results in an error.</p>\n <ul>\n <li>\n <code>true</code> indicates the background page is to be kept in\n memory from when the extension is loaded or the browser starts until\n the extension is unloaded or disabled, or the browser is closed\n (that is, the background page is persistent).\n </li>\n <li>\n <code>false</code> indicates the background page may be unloaded\n from memory when idle and recreated when needed. Such background\n pages are often called Event Pages, because they are loaded into\n memory to allow the background page to handle the events to which it\n has added listeners. Registration of listeners is persistent when\n the page is unloaded from memory, but other values are not\n persistent. If you want to store data persistently in an event page,\n then you should use the\n <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage\">storage API</a>.\n </li>\n </ul>\n </td>\n </tr>\n <tr>\n <td><code>type</code></td>\n <td>\n <p>A <code>String</code> value.</p>\n <p>Determines whether the scripts specified in <code>\"scripts\"</code> are loaded as ES modules.</p>\n <ul>\n <li><code>classic</code> indicates the background scripts or service workers are not included as an ES Module.</li>\n <li><code>module</code> indicates the background scripts or service workers are included as an ES Module. This enables the background page or service worker to <code>import</code> code.</li>\n </ul>\n <p>If omitted, this property defaults to <code>classic</code>.</p>\n </td>\n </tr>\n </tbody>\n</table></figure>"}},{"type":"prose","value":{"id":"browser_support","title":"Browser support","isH3":false,"content":"<p>Support for the <code>scripts</code>, <code>page</code>, and <code>service_worker</code> properties varies between browsers like this:</p>\n<ul>\n <li>Chrome:\n <ul>\n <li>supports <code>background.service_worker</code>.</li>\n <li>supports <code>background.scripts</code> (and <code>background.page</code>) in Manifest V2 extensions only.</li>\n <li>before Chrome 121, Chrome refuses to load a Manifest V3 extension with <code>background.scripts</code> or <code>background.page</code> present. From Chrome 121, their presence in a Manifest V3 extension is ignored.</li>\n </ul>\n </li>\n <li>Firefox:\n <ul>\n <li><code>background.service_worker</code> is not supported (see <a href=\"https://bugzil.la/1573659\" class=\"external\" target=\"_blank\">Firefox bug 1573659</a>).</li>\n <li>supports <code>background.scripts</code> (or <code>background.page</code>) if <code>service_worker</code> is not specified or the service worker feature is disabled. Before Firefox 120, Firefox did not start the background page if <code>service_worker</code> was present (see <a href=\"https://bugzil.la/1860304\" class=\"external\" target=\"_blank\">Firefox bug 1860304</a>). From Firefox 121, the background page starts as expected, regardless of the presence of <code>service_worker</code>.</li>\n </ul>\n </li>\n <li>Safari:\n <ul>\n <li>supports <code>background.service_worker</code>.</li>\n <li>supports <code>background.scripts</code> (or <code>background.page</code>) if <code>service_worker</code> is not specified.</li>\n </ul>\n </li>\n</ul>\n<p>To illustrate, this is an example of a cross-browser extension that supports <code>scripts</code> and <code>service_worker</code>. The example has this manifest.json file:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">json</span></div><pre class=\"brush: json notranslate\"><code>{\n \"name\": \"Demo of service worker + event page\",\n \"version\": \"1\",\n \"manifest_version\": 3,\n \"background\": {\n \"scripts\": [\"background.js\"],\n \"service_worker\": \"background.js\"\n }\n}\n</code></pre></div>\n<p>And, background.js contains:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">javascript</span></div><pre class=\"brush: javascript notranslate\"><code>if (typeof browser == \"undefined\") {\n // Chrome does not support the browser namespace yet.\n globalThis.browser = chrome;\n}\nbrowser.runtime.onInstalled.addListener(() => {\n browser.tabs.create({ url: \"http://example.com/first-run.html\" });\n});\n</code></pre></div>\n<p>When the extension is executed, this happens:</p>\n<ul>\n <li>in Chrome, the <code>service_worker</code> property is used, and a service worker starts that opens the tab because, in a Manifest V3 extension, Chrome only supports service workers for background scripts.</li>\n <li>in Firefox, the <code>scripts</code> property is used, and a script starts that opens the tab because Firefox only supports scripts for background scripts.</li>\n <li>in Safari, the <code>service_worker</code> property is used, and a service worker starts that opens the tab because Safari gives priority to using service workers for background scripts.</li>\n</ul>"}},{"type":"prose","value":{"id":"examples","title":"Examples","isH3":false,"content":"<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">json</span></div><pre class=\"brush: json notranslate\"><code> \"background\": {\n \"scripts\": [\"jquery.js\", \"my-background.js\"]\n }\n</code></pre></div>\n<p>Load two background scripts.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">json</span></div><pre class=\"brush: json notranslate\"><code> \"background\": {\n \"page\": \"my-background.html\"\n }\n</code></pre></div>\n<p>Load a custom background page.</p>"}},{"type":"browser_compatibility","value":{"title":"Browser compatibility","id":"browser_compatibility","isH3":false,"query":"webextensions.manifest.background"}}],"toc":[{"text":"Browser support","id":"browser_support"},{"text":"Examples","id":"examples"},{"text":"Browser compatibility","id":"browser_compatibility"}],"summary":"Use the background key to include one or more background scripts, a background page, or a Service worker in your extension.","popularity":0,"modified":"2024-11-21T19:49:47.000Z","other_translations":[{"locale":"de","title":"background","native":"Deutsch"},{"locale":"fr","title":"background","native":"Français"},{"locale":"ja","title":"background","native":"日本語"},{"locale":"ru","title":"ключ background","native":"Русский"},{"locale":"zh-CN","title":"后台 - background","native":"中文 (简体)"},{"locale":"zh-TW","title":"background","native":"正體中文 (繁體)"}],"pageType":"webextension-manifest-key","source":{"folder":"en-us/mozilla/add-ons/webextensions/manifest.json/background","github_url":"https://github.com/mdn/content/blob/main/files/en-us/mozilla/add-ons/webextensions/manifest.json/background/index.md","last_commit_url":"https://github.com/mdn/content/commit/93b34fcdb9cf91ff44f5dfe7f4dcd13e961962da","filename":"index.md"},"short_title":"background","parents":[{"uri":"/en-US/docs/Mozilla","title":"Mozilla"},{"uri":"/en-US/docs/Mozilla/Add-ons","title":"Add-ons"},{"uri":"/en-US/docs/Mozilla/Add-ons/WebExtensions","title":"Browser extensions"},{"uri":"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json","title":"manifest.json"},{"uri":"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background","title":"background"}],"pageTitle":"background - Mozilla | MDN","noIndexing":false}}</script></body></html>