index.md

---

title: cookies.onChanged
slug: Mozilla/Add-ons/WebExtensions/API/cookies/onChanged
page-type: webextension-api-event
tags:
  - API
  - Add-ons
  - Cookies
  - Event
  - Extensions
  - Non-standard
  - Reference
  - WebExtensions
  - onChanged
browser-compat: webextensions.api.cookies.onChanged

---

{{AddonSidebar()}}

The onChanged event of the {{WebExtAPIRef("cookies")}} API fires when a cookie that the extension can access is set or removed.

Note: When storage partitioning is active, cookies.Cookie.partitionKey contains the description of the cookie's storage partition. When modifying cookies, it's important to pass this value to {{WebExtAPIRef("cookies.set()")}} or {{WebExtAPIRef("cookies.remove()")}} to ensure the extension works with the correct cookie.

Note that updating a cookie's properties is implemented as a two step process:

1. First, the cookie to be updated is first removed entirely, generating a notification with a {{WebExtAPIRef("cookies.OnChangedCause")}} of overwrite.

2. Next, a new cookie is written with the updated values, generating a second notification with a {{WebExtAPIRef("cookies.OnChangedCause")}} of explicit.

Syntax

browser.cookies.onChanged.addListener(listener)
browser.cookies.onChanged.removeListener(listener)
browser.cookies.onChanged.hasListener(listener)

This API is also available as browser.cookies.onChanged.*.

Events have three functions:

• addListener(callback)

  • : Adds a listener to this event.

• removeListener(listener)

  • : Stop listening to this event. The listener argument is the listener to remove.

• hasListener(listener)

  • : Check whether listener is registered for this event. Returns true if it is listening, false otherwise.

addListener syntax

Parameters

• callback

  • : A callback function that will be called when this event occurs. The function will be passed the following arguments:

    • changeInfo

      • : An object containing details of the change that occurred. Its properties are as follows:

        • removed

          • : A boolean that is set to true if a cookie was removed, and false if not.

        • cookie

          • : A {{WebExtAPIRef('cookies.Cookie')}} object containing information about the cookie that was set or removed.

        • cause

          • : A {{WebExtAPIRef('cookies.OnChangedCause')}} value representing the underlying reason behind the cookie's change.

Browser compatibility

{{Compat}}

Examples

This example listens for onChanged events and logs details from the changeInfo argument:

browser.cookies.onChanged.addListener((changeInfo) => {
  console.log(`Cookie changed: \n`
    + ` * Cookie: ${JSON.stringify(changeInfo.cookie)}\n`
    + ` * Cause: ${changeInfo.cause}\n`
    + ` * Removed: ${changeInfo.removed}`);
});

{{WebExtExamples}}

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