chrome.storage

Description

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

Permissions

storage

Overview

The Storage API provides an extension-specific way to persist user data and state. It's similar to the web platform's storage APIs (IndexedDB, and Storage), but was designed to meet the storage needs of extensions. The following are a few key features:

  • All extension contexts, including the extension service worker and content scripts have access to the Storage API.
  • The JSON serializable values are stored as object properties.
  • The Storage API is asynchronous with bulk read and write operations.
  • Even if the user clears the cache and browsing history, the data persists.
  • Stored settings persist even when using split incognito.
  • Includes an exclusive read-only managed storage area for enterprise policies.

Even though extensions can use the [Storage][mdn-storage] interface (accessible from window.localStorage) in some contexts (popup and other HTML pages), it is not recommended for the following reasons:

  • Extension's service worker cannot access Storage.
  • Content scripts share storage with the host page.
  • Data saved using the Storage interface is lost when the user clears their browsing history.

To move data from web storage APIs to extension storage APIs from a service worker:

  1. Create an offscreen document with a conversion routine and an [onMessage][on-message] handler.
  2. Add a conversion routine to an offscreen document.
  3. In the extension service worker check chrome.storage for your data.
  4. If your data isn't found, [create][create-offscreen] an offscreen document and call [sendMessage()][send-message] to start the conversion routine.
  5. Inside the offscreen document's onMessage handler, call the conversion routine.

There are also some nuances with how web storage APIs work in extensions. Learn more in the [Storage and Cookies][storage-and-cookies] article.

Storage areas

The Storage API is divided into the following four buckets ("storage areas"):

storage.local
Data is stored locally, which is cleared when the extension is removed. The quota limitation is approximately 10 MB, but can be increased by requesting the "unlimitedStorage" permission. Consider using it to store larger amounts of data.
storage.sync
If syncing is enabled, the data is synced to any Chrome browser that the user is logged into. If disabled, it behaves like storage.local. Chrome stores the data locally when the browser is offline and resumes syncing when it's back online. The quota limitation is approximately 100 KB, 8 KB per item. Consider using it to preserve user settings across synced browsers.
storage.session
Holds data in memory for the duration of a browser session. By default, it's not exposed to content scripts, but this behavior can be changed by setting chrome.storage.session.setAccessLevel(). The quota limitation is approximately 10 MB. Consider using it to store global variables across service worker runs.
storage.managed
Administrators can use a schema and enterprise policies to configure a supporting extension's settings in a managed environment. This storage area is read-only.

Manifest

To use the storage API, declare the "storage" permission in the extension manifest. For example:

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

Usage

The following samples demonstrate the local, sync, and session storage areas:

storage.local

chrome.storage.local.set({ key: value }).then(() => {
  console.log("Value is set");
});

chrome.storage.local.get(["key"]).then((result) => {
  console.log("Value currently is " + result.key);
});

storage.sync

chrome.storage.sync.set({ key: value }).then(() => {
  console.log("Value is set");
});

chrome.storage.sync.get(["key"]).then((result) => {
  console.log("Value currently is " + result.key);
});

storage.session

chrome.storage.session.set({ key: value }).then(() => {
  console.log("Value was set");
});

chrome.storage.session.get(["key"]).then((result) => {
  console.log("Value currently is " + result.key);
});

To learn more about the managed storage area, see Manifest for storage areas.

Storage and throttling limits

Don't think of adding to the Storage API as putting things in a big truck. Think of adding to storage as being like putting something in a pipe. The pipe may have material in it already, and it may even be filled. Always assume a delay between when you add to storage and when it is actually recorded.

For details on storage area limitations and what happens when they are exceeded, see the quota information for sync, local, and session.

Use cases

The following sections demonstrate common use cases for the Storage API.

Synchronous response to storage updates

To track changes made to storage, you can add a listener to its onChanged event. When anything changes in storage, that event fires. The sample code listens for these changes:

background.js:

chrome.storage.onChanged.addListener((changes, namespace) => {
  for (let [key, { oldValue, newValue }] of Object.entries(changes)) {
    console.log(
      `Storage key "${key}" in namespace "${namespace}" changed.`,
      `Old value was "${oldValue}", new value is "${newValue}".`
    );
  }
});

We can take this idea even further. In this example, we have an options page that allows the user to toggle a "debug mode" (implementation not shown here). The options page immediately saves the new settings to storage.sync, and the service worker uses storage.onChanged to apply the setting as soon as possible.

options.html:

<!-- type="module" allows you to use top level await -->
<script defer src="options.js" type="module"></script>
<form id="optionsForm">
  <label for="debug">
    <input type="checkbox" name="debug" id="debug">
    Enable debug mode
  </label>
</form>

options.js:

// In-page cache of the user's options
const options = {};
const optionsForm = document.getElementById("optionsForm");

// Immediately persist options changes
optionsForm.debug.addEventListener("change", (event) => {
  options.debug = event.target.checked;
  chrome.storage.sync.set({ options });
});

// Initialize the form with the user's option settings
const data = await chrome.storage.sync.get("options");
Object.assign(options, data.options);
optionsForm.debug.checked = Boolean(options.debug);

background.js:

function setDebugMode() { /* ... */ }

// Watch for changes to the user's options & apply them
chrome.storage.onChanged.addListener((changes, area) => {
  if (area === 'sync' && changes.options?.newValue) {
    const debugMode = Boolean(changes.options.newValue.debug);
    console.log('enable debug mode?', debugMode);
    setDebugMode(debugMode);
  }
});

Asynchronous preload from storage

Since service workers are not always running, Manifest V3 extensions sometimes need to asynchronously load data from storage before they execute their event handlers. To do this, the following snippet uses an async action.onClicked event handler that waits for the storageCache global to be populated before executing its logic.

background.js:

// Where we will expose all the data we retrieve from storage.sync.
const storageCache = { count: 0 };
// Asynchronously retrieve data from storage.sync, then cache it.
const initStorageCache = chrome.storage.sync.get().then((items) => {
  // Copy the data retrieved from storage into storageCache.
  Object.assign(storageCache, items);
});

chrome.action.onClicked.addListener(async (tab) => {
  try {
    await initStorageCache;
  } catch (e) {
    // Handle error that occurred during storage initialization.
  }

  // Normal action handler logic.
  storageCache.count++;
  storageCache.lastTabId = tab.id;
  chrome.storage.sync.set(storageCache);
});

Extension examples

To see other demos of the Storage API, explore any of the following examples:

Types

AccessLevel

Chrome 102+

The storage area's access level.

Enum

"TRUSTED_CONTEXTS"
Specifies contexts originating from the extension itself.

"TRUSTED_AND_UNTRUSTED_CONTEXTS"
Specifies contexts originating from outside the extension.

StorageArea

Properties

  • onChanged

    Event<functionvoidvoid>

    Chrome 73+

    Fired when one or more items change.

    The onChanged.addListener function looks like:

    (callback: function)=> {...}

    • callback

      function

      The callback parameter looks like:

      (changes: object)=>void

      • changes

        object

  • clear

    void

    Promise

    Removes all items from storage.

    The clear function looks like:

    (callback?: function)=> {...}

    • callback

      function optional

      The callback parameter looks like:

      ()=>void

    • returns

      Promise<void>

      Chrome 88+

      Promises are only supported for Manifest V3 and later, other platforms need to use callbacks.

  • get

    void

    Promise

    Gets one or more items from storage.

    The get function looks like:

    (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 optional

      The callback parameter looks like:

      (items: object)=>void

      • items

        object

        Object with items in their key-value mappings.

    • returns

      Promise<object>

      Chrome 88+

      Promises are only supported for Manifest V3 and later, other platforms need to use callbacks.

  • getBytesInUse

    void

    Promise

    Gets the amount of space (in bytes) being used by one or more items.

    The getBytesInUse function looks like:

    (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 optional

      The callback parameter looks like:

      (bytesInUse: number)=>void

      • bytesInUse

        number

        Amount of space being used in storage, in bytes.

    • returns

      Promise<number>

      Chrome 88+

      Promises are only supported for Manifest V3 and later, other platforms need to use callbacks.

  • remove

    void

    Promise

    Removes one or more items from storage.

    The remove function looks like:

    (keys: string|string[],callback?: function)=> {...}

    • keys

      string|string[]

      A single key or a list of keys for items to remove.

    • callback

      function optional

      The callback parameter looks like:

      ()=>void

    • returns

      Promise<void>

      Chrome 88+

      Promises are only supported for Manifest V3 and later, other platforms need to use callbacks.

  • set

    void

    Promise

    Sets multiple items.

    The set function looks like:

    (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 optional

      The callback parameter looks like:

      ()=>void

    • returns

      Promise<void>

      Chrome 88+

      Promises are only supported for Manifest V3 and later, other platforms need to use callbacks.

  • setAccessLevel

    void

    Promise Chrome 102+

    Sets the desired access level for the storage area. The default will be only trusted contexts.

    The setAccessLevel function looks like:

    (accessOptions: object,callback?: function)=> {...}

    • accessOptions

      object

      • accessLevel

        The access level of the storage area.

    • callback

      function optional

      The callback parameter looks like:

      ()=>void

    • returns

      Promise<void>

      Promises are only supported for Manifest V3 and later, other platforms need to use callbacks.

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

Properties

  • QUOTA_BYTES

    10485760

    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 when using a callback, or a rejected Promise if using async/await.

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.

session

Chrome 102+ MV3+

Items in the session storage area are stored in-memory and will not be persisted to disk.

Type

Properties

  • QUOTA_BYTES

    10485760

    The maximum amount (in bytes) of data that can be stored in memory, as measured by estimating the dynamically allocated memory usage of every value and key. Updates that would cause this limit to be exceeded fail immediately and set runtime.lastError when using a callback, or when a Promise is rejected.

sync

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

Type

Properties

  • MAX_ITEMS

    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 when using a callback, or when a Promise is rejected.

  • MAX_SUSTAINED_WRITE_OPERATIONS_PER_MINUTE

    1000000

    Deprecated

    The storage.sync API no longer has a sustained write operation quota.

  • MAX_WRITE_OPERATIONS_PER_HOUR

    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 when using a callback, or when a Promise is rejected.

  • MAX_WRITE_OPERATIONS_PER_MINUTE

    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 when using a callback, or when a Promise is rejected.

  • QUOTA_BYTES

    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 when using a callback, or when a Promise is rejected.

  • QUOTA_BYTES_PER_ITEM

    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 when using a callback, or when a Promise is rejected.

Events

onChanged

chrome.storage.onChanged.addListener(
  callback: function,
)

Fired when one or more items change.

Parameters

  • callback

    function

    The callback parameter looks like:

    (changes: object,areaName: string)=>void

    • changes

      object

    • areaName

      string