chrome.storage

Description
Use the chrome.storage API to store, retrieve, and track changes to user data.
Permissions
storage

Overview #

This API has been optimized to meet the specific storage needs of extensions. It provides the same storage capabilities as the localStorage API with the following key differences:

User data can be automatically synced with Chrome sync (using storage.sync).
Your extension's content scripts can directly access user data without the need for a background page.
A user's extension settings can be persisted even when using split incognito behavior.
It's asynchronous with bulk read and write operations, and therefore faster than the blocking and serial localStorage API.
User data can be stored as objects (the localStorage API stores data in strings).
Enterprise policies configured by the administrator for the extension can be read (using storage.managed with a schema).

Manifest #

You must declare the "storage" permission in the extension manifest to use the storage API. For example:

{
  "name": "My extension",
  ...
  "permissions": [
    "storage"
  ],
  ...
}

Usage #

To store user data for your extension, you can use either storage.sync:

chrome.storage.sync.set({key: value}, function() {
  console.log('Value is set to ' + value);
});

chrome.storage.sync.get(['key'], function(result) {
  console.log('Value currently is ' + result.key);
});

or storage.local:

chrome.storage.local.set({key: value}, function() {
  console.log('Value is set to ' + value);
});

chrome.storage.local.get(['key'], function(result) {
  console.log('Value currently is ' + result.key);
});

When using storage.sync, the stored data will automatically be synced to any Chrome browser that the user is logged into, provided the user has sync enabled.

When Chrome is offline, Chrome stores the data locally. The next time the browser is online, Chrome syncs the data. Even if a user disables syncing, storage.sync will still work. In this case, it will behave identically to storage.local.

Warning

Confidential user information should not be stored! The storage area isn't encrypted.

The storage.managed storage is read-only.

Storage and throttling limits #

chrome.storage is not a big truck. It's a series of tubes. And if you don't understand, those tubes can be filled, and if they are filled when you put your message in, it gets in line, and it's going to be delayed by anyone that puts into that tube enormous amounts of material.

For details on the current limits of the storage API, and what happens when those limits are exceeded, please see the quota information for sync and local.

Examples #

The following example checks for CSS code saved by a user on a form, and if found, stores it.

function saveChanges() {
  // Get a value saved in a form.
  var theValue = textarea.value;
  // Check that there's some code there.
  if (!theValue) {
    message('Error: No value specified');
    return;
  }
  // Save it using the Chrome extension storage API.
  chrome.storage.sync.set({'value': theValue}, function() {
    // Notify that we saved.
    message('Settings saved');
  });
}

If you're interested in tracking changes made to a data object, you can add a listener to its onChanged event. Whenever anything changes in storage, that event fires. Here's sample code to listen for saved changes:

chrome.storage.onChanged.addListener(function(changes, namespace) {
  for (var key in changes) {
    var storageChange = changes[key];
    console.log('Storage key "%s" in namespace "%s" changed. ' +
                'Old value was "%s", new value is "%s".',
                key,
                namespace,
                storageChange.oldValue,
                storageChange.newValue);
  }
});

Summary

Types
StorageArea
StorageChange
Properties
local
managed
sync
Events
onChanged

Types

StorageArea

Properties

onChanged
events.Event<function>
Fired when one or more items change.
Add a listener like this:
onChanged.addListener(listener)
- listener
  function
  The listener parameter should be a function that looks like this:
  (changes: object) => {...}
  changes
  object
  Object mapping each key that changed to its corresponding StorageChange for that item.
clear
function
Removes all items from storage.
The clear function looks like this:
clear(callback: function) => {...}
- callback
  function
  Callback on success, or on failure (in which case runtime.lastError will be set).
  The callback parameter should be a function that looks like this:
  () => {...}
get
function
Gets one or more items from storage.
The get function looks like this:
get(keys?: string | string[] | object, callback: function) => {...}
- keys
  string | string[] | object optional
  A single key to get, list of keys to get, or a dictionary specifying default values (see description of the object). An empty list or object will return an empty result object. Pass in null to get the entire contents of storage.
- callback
  function
  Callback with storage items, or on failure (in which case runtime.lastError will be set).
  The callback parameter should be a function that looks like this:
  (items: object) => {...}
  items
  object
  Object with items in their key-value mappings.
getBytesInUse
function
Gets the amount of space (in bytes) being used by one or more items.
The getBytesInUse function looks like this:
getBytesInUse(keys?: string | string[], callback: function) => {...}
- keys
  string | string[] optional
  A single key or list of keys to get the total usage for. An empty list will return 0. Pass in null to get the total usage of all of storage.
- callback
  function
  Callback with the amount of space being used by storage, or on failure (in which case runtime.lastError will be set).
  The callback parameter should be a function that looks like this:
  (bytesInUse: number) => {...}
  bytesInUse
  number
  Amount of space being used in storage, in bytes.
remove
function
Removes one or more items from storage.
The remove function looks like this:
remove(keys: string | string[], callback: function) => {...}
- keys
  string | string[]
  A single key or a list of keys for items to remove.
- callback
  function
  Callback on success, or on failure (in which case runtime.lastError will be set).
  The callback parameter should be a function that looks like this:
  () => {...}
set
function
Sets multiple items.
The set function looks like this:
set(items: object, callback: function) => {...}
- items
  object
  An object which gives each key/value pair to update storage with. Any other key/value pairs in storage will not be affected.
  Primitive values such as numbers will serialize as expected. Values with a typeof "object" and "function" will typically serialize to {}, with the exception of Array (serializes as expected), Date, and Regex (serialize using their String representation).
- callback
  function
  Callback on success, or on failure (in which case runtime.lastError will be set).
  The callback parameter should be a function that looks like this:
  () => {...}

StorageChange

Properties

newValue
any optional
The new value of the item, if there is a new value.
oldValue
any optional
The old value of the item, if there was an old value.

Properties

local

Items in the local storage area are local to each machine.

Type

StorageArea

Properties

QUOTA_BYTES
number 5242880
The maximum amount (in bytes) of data that can be stored in local storage, as measured by the JSON stringification of every value plus every key's length. This value will be ignored if the extension has the unlimitedStorage permission. Updates that would cause this limit to be exceeded fail immediately and set runtime.lastError.

managed

Items in the managed storage area are set by the domain administrator, and are read-only for the extension; trying to modify this namespace results in an error.

Type

StorageArea

sync

Items in the sync storage area are synced using Chrome Sync.

Type

StorageArea

Properties

MAX_ITEMS
number 512
The maximum number of items that can be stored in sync storage. Updates that would cause this limit to be exceeded will fail immediately and set runtime.lastError.
MAX_SUSTAINED_WRITE_OPERATIONS_PER_MINUTE
number 1000000
Deprecated. The storage.sync API no longer has a sustained write operation quota.
MAX_WRITE_OPERATIONS_PER_HOUR
number 1800
The maximum number of set, remove, or clear operations that can be performed each hour. This is 1 every 2 seconds, a lower ceiling than the short term higher writes-per-minute limit.
Updates that would cause this limit to be exceeded fail immediately and set runtime.lastError.
MAX_WRITE_OPERATIONS_PER_MINUTE
number 120
The maximum number of set, remove, or clear operations that can be performed each minute. This is 2 per second, providing higher throughput than writes-per-hour over a shorter period of time.
Updates that would cause this limit to be exceeded fail immediately and set runtime.lastError.
QUOTA_BYTES
number 102400
The maximum total amount (in bytes) of data that can be stored in sync storage, as measured by the JSON stringification of every value plus every key's length. Updates that would cause this limit to be exceeded fail immediately and set runtime.lastError.
QUOTA_BYTES_PER_ITEM
number 8192
The maximum size (in bytes) of each individual item in sync storage, as measured by the JSON stringification of its value plus its key length. Updates containing items larger than this limit will fail immediately and set runtime.lastError.

Events

onChanged

chrome.storage.onChanged.addListener(listener: function)

Fired when one or more items change.

Event

listener
function
The listener parameter should be a function that looks like this:
(changes: object, areaName: string) => {...}
- changes
  object
  Object mapping each key that changed to its corresponding StorageChange for that item.
- areaName
  string
  The name of the storage area ("sync", "local" or "managed") the changes are for.