index.md

---

title: extension
slug: Mozilla/Add-ons/WebExtensions/API/extension
page-type: webextension-api
tags:
  - API
  - Add-ons
  - Extension
  - Extensions
  - Interface
  - Reference
  - WebExtensions
browser-compat: webextensions.api.extension

---

{{AddonSidebar}}

Utilities related to your extension. Get URLs to resources packages with your extension. Get the Window object for your extension's pages. Get the values for various settings.

Note: The messaging APIs in this module are deprecated in favor of the equivalent APIs in the runtime module.

Types

• {{WebExtAPIRef("extension.ViewType")}}

  • : The type of extension view.

Properties

• {{WebExtAPIRef("extension.lastError")}} {{deprecated_inline}}

  • : Set for the lifetime of a callback if an asynchronous extension API has resulted in an error. If no error has occurred, lastError will be {{jsxref("undefined")}}.

• {{WebExtAPIRef("extension.inIncognitoContext")}}

  • : True for content scripts running inside incognito tabs, and for extension pages running inside an incognito process. (The latter only applies to extensions with 'split' incognito_behavior.)

Functions

• {{WebExtAPIRef("extension.getBackgroundPage()")}}

  • : Returns the Window object for the background page running inside the current extension. Returns null if the extension has no background page.

• {{WebExtAPIRef("extension.getExtensionTabs()")}} {{deprecated_inline}}

  • : Returns an array of the JavaScript Window objects for each of the tabs running inside the current extension.

• {{WebExtAPIRef("extension.getURL()")}} {{deprecated_inline}}

  • : Converts a relative path within an extension install directory to a fully-qualified URL.

• {{WebExtAPIRef("extension.getViews()")}}

  • : Returns an array of the Window objects for each of the pages running inside the current extension.

• {{WebExtAPIRef("extension.isAllowedIncognitoAccess()")}}

  • : Retrieves the state of the extension's access to Incognito-mode (as determined by the user-controlled 'Allowed in Incognito' checkbox).

• {{WebExtAPIRef("extension.isAllowedFileSchemeAccess()")}}

  • : Retrieves the state of the extension's access to the file:// scheme (as determined by the user-controlled 'Allow access to File URLs' checkbox).

• {{WebExtAPIRef("extension.sendRequest()")}} {{deprecated_inline}}

  • : Sends a single request to other listeners within the extension.

• {{WebExtAPIRef("extension.setUpdateUrlData()")}}

  • : Sets the value of the ap CGI parameter used in the extension's update URL. This value is ignored for extensions that are hosted in the browser vendor's store.

Events

• {{WebExtAPIRef("extension.onRequest")}} {{deprecated_inline}}

  • : Fired when a request is sent from either an extension process or a content script.

• {{WebExtAPIRef("extension.onRequestExternal")}} {{deprecated_inline}}

  • : Fired when a request is sent from another extension.

Browser compatibility

{{Compat}}

{{WebExtExamples("h2")}}

Note: This API is based on Chromium's chrome.extension API. This documentation is derived from extension.json in the Chromium code.