chrome.storage

Description

Permissions

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

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

Examples

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

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

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

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

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

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

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

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

• Global search extension.
• Water alarm extension.

Concepts and usage

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.

Can extensions use web storage APIs?

While extensions can use the Storage interface (accessible from window.localStorage) in some contexts (popup and other HTML pages), we don't recommend it for the following reasons:

• Extension service workers can't use the Web Storage API.
• Content scripts share storage with the host page.
• Data saved using the Web Storage API 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. Prepare an offscreen document html page and script file. The script file should contain a conversion routine and an onMessage handler.
2. In the extension service worker, check chrome.storage for your data.
3. If your data isn't found, call createDocument().
4. After the returned Promise resolves, call sendMessage() to start the conversion routine.
5. Inside the offscreen document's onMessage handler, call the conversion routine.

There are also some nuances to how web storage APIs work in extensions. Learn more in the Storage and Cookies article.

Storage and throttling limits

The Storage API has usage limitations:

• Storing data has performance costs, and the API includes storage quotas. Plan the data you intend to store, so you maintain storage space.
• Storage can take time to complete. Structure your code to account for that time.

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

Storage areas

The Storage API is divided into the following storage areas:

Local

Data is stored locally and cleared when the extension is removed. The storage limit is 10 MB (5 MB in Chrome 113 and earlier), but can be increased by requesting the "unlimitedStorage" permission. We recommend using storage.local to store larger amounts of data. By default, it's exposed to content scripts, but this behavior can be changed by calling chrome.storage.local.setAccessLevel().

Managed

Managed storage is read-only for policy-installed extensions. It's managed by system administrators, using a developer-defined schema and enterprise policies. Policies are similar to options but are configured by a system administrator, instead of the user. This allows the extension to be preconfigured for all users of an organization.

By default, storage.managed is exposed to content scripts, but this behavior can be changed by calling chrome.storage.managed.setAccessLevel(). For information on policies, see Documentation for Administrators. To learn more about the managed storage area, see Manifest for storage areas.

Session

Session storage holds data in memory while an extension is loaded. The storage is cleared if the extension is disabled, reloaded, updated, and when the browser restarts. By default, it's not exposed to content scripts, but this behavior can be changed by calling chrome.storage.session.setAccessLevel(). The storage limit is 10 MB (1 MB in Chrome 111 and earlier).

Thestorage.session interface is one of several we recommend for service workers.

Sync

If the user enables syncing, the data syncs with every 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.

We recommend using storage.sync to preserve user settings across synced browsers. If you're working with sensitive user data, instead use storage.session. By default, storage.sync is exposed to content scripts, but this behavior can be changed by calling chrome.storage.sync.setAccessLevel().

Methods and events

All storage areas implement the StorageArea interface.

get()

The get() method lets you read one or more keys from a StorageArea.

getBytesInUse()

The getBytesInUse() method lets you see the quota used by a StorageArea.

getKeys()

The getKeys() method lets you get all keys stored in a StorageArea.

remove()

The remove() method lets you remove an item from a StorageArea.

set()

The set() method lets you set an item in a StorageArea.

setAccessLevel()

The setAccessLevel() method lets you control access to a StorageArea.

clear()

The clear() method lets you clear all data from a StorageArea.

onChanged

The onChanged event lets you monitor changes to a StorageArea.

Use cases

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

Respond to storage updates

To track changes made to storage, 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

Because service workers don't run all the time, 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);
});

DevTools

You can view and edit data stored using the API in DevTools. To learn more, see the View and edit extension storage page in the DevTools documentation.

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