---
title: cookies.OnChangedCause
slug: Mozilla/Add-ons/WebExtensions/API/cookies/OnChangedCause
tags:
  - API
  - Add-ons
  - Cookies
  - Extensions
  - Non-standard
  - OnChangedCause
  - Reference
  - Type
  - WebExtensions
browser-compat: webextensions.api.cookies.OnChangedCause
---
{{AddonSidebar()}}

The `OnChangedCause` type of the {{WebExtAPIRef("cookies")}} API represents the reason a cookie changed.

## Type

Values of this type are strings. Possible values are:

- `evicted`
  - : A cookie has been automatically removed due to garbage collection.
- `expired`
  - : A cookie has been automatically removed due to expiry.
- `explicit`
  - : A cookie has been inserted or removed via an explicit call to {{WebExtAPIRef("cookies.remove()")}}.
- `expired_overwrite`
  - : A cookie has been overwritten by a cookie with an already-expired expiration date.
- `overwrite`
  - : A call to {{WebExtAPIRef("cookies.set()")}} overwrote this cookie with a different one.

## Browser compatibility

{{Compat}}

## Examples

You can listen to the {{WebExtAPIRef("cookies.onChanged")}} event to be notified when cookies change. The listener is passed a `changeInfo` object that contains a `cause` property, whose value is the `OnChangeCaused` string:

```js
browser.cookies.onChanged.addListener(function(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`](https://developer.chrome.com/extensions/cookies#type-OnChangedCause) API. This documentation is derived from [`cookies.json`](https://chromium.googlesource.com/chromium/src/+/master/chrome/common/extensions/api/cookies.json) in the Chromium code.
>
> Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.

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