Enables extensions to store and retrieve data, and listen for changes to stored items.
The storage system is based on the Web Storage API, with a few differences. Among other differences, these include:
- It's asynchronous.
- Values are scoped to the extension, not to a specific domain (i.e. the same set of key/value pairs are available to all scripts in the background context and content scripts).
- The values stored can be any JSON-ifiable value, not just
String
. Among other things, this includes:Array
andObject
, but only when their contents can be represented as JSON, which does not include DOM nodes. You don't need to convert your values to JSONStrings
prior to storing them, but they are represented as JSON internally, thus the requirement that they be JSON-ifiable. - Multiple key/value pairs can be set or retrieved in the same API call.
To use this API you need to include the "storage"
permission in your manifest.json
file.
Each extension has its own storage area, which can be split into different types of storage.
Although this API is similar to Window.localStorage
it is recommended that you don't use Window.localStorage
in the extension code to store extension-related data. Firefox will clear data stored by extensions using the localStorage API in various scenarios where users clear their browsing history and data for privacy reasons, while data saved using the storage.local
API will be correctly persisted in these scenarios.
You can examine the stored data under the Extension Storage item in the Storage Inspector tab of the developer toolbox, accessible from about:debugging
.
Types
storage.StorageArea
- An object representing a storage area.
storage.StorageChange
- An object representing a change to a storage area.
Properties
storage
has three properties, which represent the different types of available storage area.
storage.sync
- Represents the
sync
storage area. Items insync
storage are synced by the browser, and are available across all instances of that browser that the user is logged into, across different devices. storage.local
- Represents the
local
storage area. Items inlocal
storage are local to the machine the extension was installed on. storage.managed
- Represents the
managed
storage area. Items inmanaged
storage are set by the domain administrator and are read-only for the extension. Trying to modify this namespace results in an error.
Events
storage.onChanged
- Fired when one or more items change in a storage area.
Browser compatibility
Desktop | Mobile | |||||
---|---|---|---|---|---|---|
StorageArea | Chrome Full support Yes | Edge Full support 14 | Firefox Full support 45 | Opera Full support Yes | Safari Full support 14 | Firefox Android Full support 48 |
StorageChange | Chrome Full support Yes | Edge Full support 14 | Firefox Full support 45 | Opera Full support Yes | Safari Full support 14 | Firefox Android Full support 48 |
local | Chrome Full support Yes | Edge Full support 14 | Firefox
Full support
45
| Opera Full support Yes | Safari Full support 14 | Firefox Android Full support 48 |
managed | Chrome Full support Yes | Edge Full support 79 | Firefox
Full support
57
| Opera No support No | Safari No support No | Firefox Android No support No |
onChanged | Chrome Full support Yes | Edge Full support 14 | Firefox Full support 45 | Opera Full support Yes | Safari Full support 14 | Firefox Android Full support 48 |
sync | Chrome Full support Yes | Edge Full support 15 | Firefox
Full support
53
| Opera No support No | Safari
Partial support
14
| Firefox Android No support No |
Legend
- Full support
- Full support
- Partial support
- Partial support
- No support
- No support
- See implementation notes.
- See implementation notes.
Example extensions
This API is based on Chromium's chrome.storage
API. This documentation is derived from storage.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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