svelte-webext-stores

Svelte stores that are synchronized with extension storage.

Note: This library is currently in alpha development, and is subject to breaking changes with or without warning.

Features

• Different storage types support: chrome.storage (either MV2 or MV3), browser.storage (including webextension-polyfill), and even non-extension storage such as window.localStorage and window.sessionStorage are supported out of the box.
• Automatically synchronizes to and from storage backend.
• TypeScript support: This library is fully written in TypeScript, and the distributed package includes TypeScript declarations.
• Custom implementations: Create and use your own custom storage backends or synchronized stores by implementing IStorageBackend or ISyncStore respectively.

Getting started

Installation

npm install -D svelte-webext-stores

or

yarn add -D svelte-webext-stores

Quick Usage

storage.js

import { webExtStores } from 'svelte-webext-stores';

// Instantiate default store handler, which is backed by MV2 chrome.storage.local
const stores = webExtStores();
// Register a new synchronized store with storage key 'count' and default value of 1
export const count = stores.addSyncStore('count', 1);

App.svelte

<script>
  import { count } from './storage.js';

  function addCount() {
    $count += 1;
  }
</script>

<button on:click={addCount}>Count: {$count}</button>

Advanced Usage

Storage Backends

This library supports and exports the following storage options out of the box. To use a provided storage option, simply import it and pass it into webExtStores.

Storage	Description
storageMV2	Chrome Manifest Version 2 (callback API).
storageMV3	Chrome Manifest Version 3 (Promise API).
storageWebExt	Mozilla WebExtension (browser API), including webextension-polyfill.
storageLegacy	Legacy/non-extension storage (localStorage or sessionStorage).

To set the storage area/type, pass the corresponding string parameter.

Storage	Allowed parameter	Default
storageMV2, storageMV3, storageWebExt	'local' | 'sync' | 'managed'	'local'
storageLegacy	'session' | 'local'	'session'

Example:

import { webExtStores, storageWebExt } from 'svelte-webext-stores';

// Uses the Mozilla WebExtension browser API in the 'sync' area.
const stores = webExtStores(storageWebExt('sync'));

More information on the IStorageBackend interface that is implemented by all the above storage backends can be found here.

Synchronized Stores

All provided synchronized stores below implements the ISyncStore interface. More information can be found here.

SyncStore

Standard store that synchronizes to the storage backend. Uses Svelte writable to implement the Svelte store contract.

WebExtStores.addSyncStore<T>(
  key: string,
  defaultValue: T,
  syncFromExternal = true,
  versionedOptions?: VersionedOptions
): SyncStore<T>

Parameter	Description
key	Storage key
defaultValue	Store's default value
syncFromExternal	Whether store should be updated when storage value is updated externally
versionedOptions	Enables options for migrating storage values from an older version to a newer version

Aside from methods derived from ISyncStore, SyncStore also contains the following methods:

Methods	Signature	Description
ready	ready: () => Promise<void>	Ensure that any async initialization process (such as initial update from backend) has been completed. You typically don't need to manually call this unless you wish to sync the store to the storage backend before any of get(), set(), subscribe() or update() is called.
reset	reset: () => Promise<void>	Reset store value to default value.
update	update: (updater: (value: T) => T) => Promise<void>	Update value using callback and inform subscribers.

LookupStore

Synchronized store for Record<string, any> objects. LookupStore is derived from and is functionally similar to SyncStore, with additional convenience methods for getting and setting the stored object's property values using property keys.

WebExtStores.addLookupStore<T extends Record<string, any>>(
  key: string,
  defaultValue: T,
  syncFromExternal = true,
  versionedOptions?: VersionedOptions<T>
): LookupStore<T>

Methods	Signature	Description
getItem	getItem: <R extends T[keyof T]>(key: keyof T) => Promise<R>	Get property value.
setItem	setItem: <V extends T[keyof T]>(key: keyof T, value: V) => Promise<void>	Set property value.

Example:

import { webExtStores } from 'svelte-webext-stores';

const stores = webExtStores();
export const obj = stores.addLookupStore('obj', { a: 1, b: false, c: '3' });


const a = await obj.getItem('a'); // Returns 1
await obj.setItem('b', true); // Object is now { a: 1, b: false, c: '3' }

You can also easily add these convenience methods to your custom ISyncStore implementations. More information can be found here.

Versioned Store Values and Migration

SyncStore and its derivatives has the optional parameter versionedOptions. When the parameter is provided, it keeps track of the current store's version to enable ease of migrating values from an older store version to the current version. This can be useful to migrate breaking changes on the stored data without reseting its value to default.

VersionedOptions properties are as follows:

Property	Type	Descrption
version	number	Current version number. Do not use -1.
seperator	string	Separator between key and version.
migrations	Map<number, (oldValue: any) => T>	Map for migrating values. Keys are the old version to match against, and values are callbacks that accepts the value found from the given old version and returns the corresponding value for the current version. Use the key -1 to migrate from a versionless store.

SyncStores that are provided with the versionedOptions parameter are stored as ${key}${seperator}${version} internally. When an older version that matches any of the keys in the Map is found, its value is passed to the callback, the returned value is stored and the old version is removed.

// Initial store
export const size = stores.addSyncStore('size', 500);

// Example usage in svelte
window.resizeTo($size, $size);

// To migrate to a new value, replace the old declaration
const sizeMigrations = new Map();
sizeMigrations.set(-1, (oldValue) => `${oldValue}x${oldValue * 2}`);

export const size = stores.addSyncStore(
  'size',
  '500x1000',
  true,
  {
    version: 1,
    seperator: '$',
    migrations: sizeMigrations
  }
);

// Example usage in svelte
const [width, height] = $size.split('x');
window.resizeTo(width, height);