Effector-storage NPM

effector-storage

Small module for Effector ☄️ to sync stores with different storages (local storage, session storage, async storage, IndexedDB, cookies, server side storage, etc).

Install

Depending on your package manager

# using `pnpm` ↓
$ pnpm add effector-storage

# using `yarn` ↓
$ yarn add effector-storage

# using `npm` ↓
$ npm install --save effector-storage

Usage

with `localStorage`

Docs: effector-storage/local

import { persist } from 'effector-storage/local'

// persist store `$counter` in `localStorage` with key 'counter'
persist({ store: $counter, key: 'counter' })

// if your storage has a name, you can omit `key` field
persist({ store: $counter })

Stores, persisted in localStorage, are automatically synced between two (or more) windows/tabs. Also, they are synced between instances, so if you will persist two stores with the same key — each store will receive updates from another one.

ℹ️ If you need just basic bare minimum functionality, you can take a look at effector-localstorage library. It has similar API, it much simpler and tinier.

with `sessionStorage`

Docs: effector-storage/session

Same as above, just import persist from 'effector-storage/session':

import { persist } from 'effector-storage/session'

Stores, persisted in sessionStorage, are synced between instances, but not between different windows/tabs.

with query string

Docs: effector-storage/query

You can reflect plain string store value in query string parameter, using this adapter. Think of it like about synchronizing store value and query string parameter.

import { persist } from 'effector-storage/query'

// persist store `$id` in query string parameter 'id'
persist({ store: $id, key: 'id' })

If two (or more) stores are persisted in query string with the same key — they are synced between themselves.

with `BroadcastChannel`

Docs: effector-storage/broadcast

You can sync stores across different browsing contexts (tabs, windows, workers), just import persist from 'effector-storage/broadcast':

import { persist } from 'effector-storage/broadcast'

extra adapters

You can find a collection of useful adapters in effector-storage-extras. That side repository was created in order to not bloat effector-storage with dependencies and adapters, which depends on other libraries.

Usage with domains

You can use persist inside Domain's onCreateStore hook:

import { createDomain } from 'effector'
import { persist } from 'effector-storage/local'

const app = createDomain('app')

// this hook will persist every store, created in domain,
// in `localStorage`, using stores' names as keys
app.onCreateStore((store) => persist({ store }))

const $store = app.createStore(0, { name: 'store' })

Formulae

import { persist } from 'effector-storage/<adapter>'

persist({ store, ...options }): Subscription
persist({ source, target, ...options }): Subscription

Units

In order to synchronize something, you need to specify effector units. Depending on a requirements, you may want to use store parameter, or source and target parameters:

store (Store): Store to synchronize with local/session storage.
source (Event | Effect | Store): Source unit, which updates will be sent to local/session storage.
target (Event | Effect | Store): Target unit, which will receive updates from local/session storage (as well as initial value). Must be different than source to avoid circular updates — source updates are passed directly to target.

Options

key? (string): Key for local/session storage, to store value in. If omitted — store name is used. Note! If key is not specified, store must have a name! You can use 'effector/babel-plugin' to have those names automatically.
keyPrefix? (string): Prefix, used in adapter, to be concatenated to key. By default = ''.
clock? (Event | Effect | Store): Unit, if passed – then value from store/source will be stored in the storage only upon its trigger.
pickup? (Event | Effect | Store): Unit, which you can specify to update store value from storage. This unit can also set a special context for adapter. Note! When you add pickup, persist will not get initial value from storage automatically!
context? (Event | Effect | Store): Unit, which can set a special context for adapter.
contract? (Contract): Rule to statically validate data from storage.
done? (Event | Effect | Store): Unit, which will be triggered on each successful read or write from/to storage. Payload structure:
- key (string): Same key as above.
- keyPrefix (string): Prefix, used in adapter, to be concatenated to key. By default = ''.
- operation ('set' | 'get'): Type of operation, read (get) or write (set).
- value (State): Value set to store or got from store.
fail? (Event | Effect | Store): Unit, which will be triggered in case of any error (serialization/deserialization error, storage is full and so on). Note! If fail unit is not specified, any errors will be printed using console.error(Error). Payload structure:
- key (string): Same key as above.
- keyPrefix (string): Prefix, used in adapter, to be concatenated to key. By default = ''.
- operation ('set' | 'get' | 'validate'): Type of operation, read (get), write (set) or validation against contract (validate).
- error (Error): Error instance
- value? (any): In case of 'set' operation — value from store. In case of 'get' operation could contain raw value from storage or could be empty.
finally? (Event | Effect | Store): Unit, which will be triggered either in case of success or error. Payload structure:
- key (string): Same key as above.
- keyPrefix (string): Prefix, used in adapter, to be concatenated to key. By default = ''.
- operation ('set' | 'get' | 'validate'): Type of operation, read (get), write (set) or validation against contract (validate).
- status ('done' | 'fail'): Operation status.
- error? (Error): Error instance, in case of error.
- value? (any): Value, in case it is exists (look above).

Returns

(Subscription): You can use this subscription to remove store association with storage, if you don't need them to be synced anymore. It is a function.

Contracts

You can use contract option to validate data from storage. Contract has the following type definition:

export type Contract<Data> =
  | ((raw: unknown) => raw is Data)
  | {
      isData: (raw: unknown) => raw is Data
      getErrorMessages: (raw: unknown) => string[]
    }

So, it could be simple type guard function in trivial use cases, or more complex object with isData type guard and getErrorMessages function, which returns array of error messages. This format is fully compatible with Farfetched contracts, so you can use any adapter from Farfetched (runtypes, zod, io-ts, superstruct, typed-contracts) with persist and contract option:

// simple type guard
persist({
  store: $counter,
  key: 'counter',
  contract: (raw): raw is number => typeof raw === 'number',
})

// complex contract with Farfetched adapter
import { Record, Literal, Number } from 'runtypes'
import { runtypeContract } from '@farfetched/runtypes'

const Asteroid = Record({
  type: Literal('asteroid'),
  mass: Number,
})

persist({
  store: $asteroid,
  key: 'asteroid',
  contract: runtypeContract(Asteroid),
})

There are two gotchas with contracts:

From effector-storage point of view it is absolutely normal, when there is no persisted value in the storage yet. So, undefined value is always valid, even if contract does not explicitly allow it.
effector-storage does not prevent persisting invalid data to the storage, but it will validate it nonetheless, after persisting, so, if you write invalid data to the storage, fail will be triggered, but data will be persisted.

Notes

Without specifying pickup property, calling persist will immediately call adapter to get initial value. In case of synchronous storage (like localStorage or sessionStorage) this action will synchronously set store value, and call done/fail/finally right away. You should take that into account, if you adds some logic on done, for example — place persist after that logic (see issue #38 for more details).

You can modify adapter to be asynchronous to mitigate this behavior with async function.

`createPersist` factory

In rare cases you might want to use createPersist factory. It allows you to specify some adapter options, like keyPrefix.

import { createPersist } from 'effector-storage/local'

const persist = createPersist({
  keyPrefix: 'app/',
})

// ---8<---

persist({
  store: $store1,
  key: 'store1', // localStorage key will be `app/store1`
})
persist({
  store: $store2,
  key: 'store2', // localStorage key will be `app/store2`
})

Options

pickup? (Event | Effect | Store): Unit, which you can specify to update store value from storage. This unit can also set a special context for adapter. Note! When you add pickup, persist will not get initial value from storage automatically!
context? (Event | Effect | Store): Unit, which can set a special context for adapter.
keyPrefix? (string): Key prefix for adapter. It will be concatenated with any key, given to returned persist function.
contract? (Contract): Rule to statically validate data from storage.

Returns

Custom persist function, with predefined adapter options.

Advanced usage

effector-storage consists of a core module and adapter modules.

The core module itself does nothing with actual storage, it just connects effector units to the storage adapter, using couple of Effects and bunch of connections.

The storage adapter gets and sets values, and also can asynchronously emit values on storage updates.

import { persist } from 'effector-storage'

Core function persist accepts all common options, as persist functions from sub-modules, plus additional one:

adapter (StorageAdapter): Storage adapter to use.

Storage adapters

Adapter is a function, which is called by the core persist function, and has following interface:

interface StorageAdapter {
  <State>(
    key: string,
    update: (raw?: any) => void
  ): {
    get(raw?: any, ctx?: any): State | Promise<State | undefined> | undefined
    set(value: State, ctx?: any): void
  }
  keyArea?: any
  noop?: boolean
}

Arguments

key (string): Unique key to distinguish values in storage.
update (Function): Function, which could be called to get value from storage. In fact this is Effect with get function as a handler. In other words, any argument, passed to update function, will end up as argument in get function.

Returns

{ get, set } ({ Function, Function }): Getter from and setter to storage. These functions are used as Effects handlers, and could be sync or async. Also, you don't have to catch exceptions and errors inside those functions — Effects will do that for you. As mentioned above, call of update function will trigger get function with the same argument. So you can handle cases, when get function is called during initial persist execution (without arguments), or after external update. Check out example below. Also getter and setter both accepts optional context as a second argument — it can be any value. This context could be useful, if adapter depends on some external environment, for example, it can contain Request and Response from Express middleware, to get/set cookies from/to. (TODO: isomorphic cookies adapter example).

keyArea

Adapter function can have static field keyArea — this could be any value of any type, which should be unique for keys namespace. For example, two local storage adapters could have different settings, but both of them uses same storage area — localStorage. So, different stores, persisted in local storage with the same key (but possibly with different adapters), should be synced. That is what keyArea is responsible for. Value of that field is used as a key in cache Map. In case it is omitted — adapter instances is used instead.

noop

Marks adapter as "no-op" for either function.

Synchronous storage adapter example

For example, simplified localStorage adapter might looks like this. This is over-simplified example, don't do that in real code, there are no serialization and deserialization, no checks for edge cases. This is just to show an idea.

import { createStore } from 'effector'
import { persist } from 'effector-storage'

const adapter = (key) => ({
  get: () => localStorage.getItem(key),
  set: (value) => localStorage.setItem(key, value),
})

const store = createStore('', { name: 'store' })
persist({ store, adapter }) // <- use adapter

Asynchronous storage adapter example

Using asynchronous storage is just as simple. Once again, this is just a bare simple idea, without serialization and edge cases checks. If you need to use React Native Async Storage, try @effector-storage/react-native-async-storage) adapter instead.

import AsyncStorage from '@react-native-async-storage/async-storage'
import { createStore } from 'effector'
import { persist } from 'effector-storage'

const adapter = (key) => ({
  get: async () => AsyncStorage.getItem(key),
  set: async (value) => AsyncStorage.setItem(key, value),
})

const store = createStore('', { name: '@store' })
persist({ store, adapter }) // <- use adapter

Storage with external updates example

If your storage can be updated from an external source, then adapter needs a way to inform/update connected store. That is where you will need second update argument.

import { createStore } from 'effector'
import { persist } from 'effector-storage'

const adapter = (key, update) => {
  addEventListener('storage', (event) => {
    if (event.key === key) {
      // kick update
      // this will call `get` function from below ↓
      // wrapped in Effect, to handle any errors
      update(event.newValue)
    }
  })

  return {
    // `get` function will receive `newValue` argument
    // from `update`, called above ↑
    get: (newValue) => newValue || localStorage.getItem(key),
    set: (value) => localStorage.setItem(key, value),
  }
}

const store = createStore('', { name: 'store' })
persist({ store, adapter }) // <- use adapter

Update from non-reactive storage

If your storage can be updated from external source, and doesn't have any events to react to, but you are able to know about it somehow.

You can use optional pickup parameter to specify unit to trigger update (keep in mind, that when you add pickup, persist will not get initial value from storage automatically):

import { createEvent, createStore } from 'effector'
import { persist } from 'effector-storage/session'

// event, which will be used to trigger update
const pickup = createEvent()

const store = createStore('', { name: 'store' })
persist({ store, pickup }) // <- set `pickup` parameter

// --8<--

// when you are sure, that storage was updated,
// and you need to update `store` from storage with new value
pickup()

Another option, if you have your own adapter, you can add this feature right into it:

import { createEvent, createStore } from 'effector'
import { persist } from 'effector-storage'

// event, which will be used in adapter to react to
const pickup = createEvent()

const adapter = (key, update) => {
  // if `pickup` event was triggered -> call an `update` function
  // this will call `get` function from below ↓
  // wrapped in Effect, to handle any errors
  pickup.watch(update)
  return {
    get: () => localStorage.getItem(key),
    set: (value) => localStorage.setItem(key, value),
  }
}

const store = createStore('', { name: 'store' })
persist({ store, adapter }) // <- use your adapter

// --8<--

// when you are sure, that storage was updated,
// and you need to force update `store` from storage with new value
pickup()

Local storage adapter with values expiration

I want sync my store with localStorage, but I need smart synchronization, not dumb. Each storage update should contain last write timestamp. And on read value I need to check if value has been expired, and fill store with default value in that case.

You can implement it with custom adapter, something like this:

import { createStore } from 'effector'
import { persist } from 'effector-storage'

const adapter = (timeout) => (key) => ({
  get() {
    const item = localStorage.getItem(key)
    if (item === null) return // no value in localStorage
    const { time, value } = JSON.parse(item)
    if (time + timeout * 1000 < Date.now()) return // value has expired
    return value
  },

  set(value) {
    localStorage.setItem(key, JSON.stringify({ time: Date.now(), value }))
  },
})

const store = createStore('', { name: 'store' })

// use adapter with timeout = 1 hour ↓↓↓
persist({ store, adapter: adapter(3600) })

Custom `Storage` adapter

Both 'effector-storage/local' and 'effector-storage/session' are using common storage adapter factory. If you want to use other storage, which implements Storage interface (in fact, synchronous getItem and setItem methods are enough) — you can use this factory.

import { storage } from 'effector-storage/storage'

adapter = storage(options)

Options

storage (Storage): Storage to communicate with.
sync? (boolean | 'force'): Add 'storage' event listener or no. Default = false. In case of 'force' value adapter will always read new value from Storage, instead of event.
serialize? ((value: any) => string): Custom serialize function. Default = JSON.stringify
deserialize? ((value: string) => any): Custom deserialize function. Default = JSON.parse

Returns

(StorageAdapter): Storage adapter, which can be used with the core persist function.

FAQ

Can I persist part of the store?

The issue here is that it is hardly possible to create universal mapping to/from storage to the part of the store within the library implementation. But with persist form with source/target, and little help of Effector API you can make it:

import { persist } from 'effector-storage/local'

const setX = createEvent()
const setY = createEvent()
const $coords = createStore({ x: 123, y: 321 })
  .on(setX, ({ y }, x) => ({ x, y }))
  .on(setY, ({ x }, y) => ({ x, y }))

// persist X coordinate in `localStorage` with key 'x'
persist({
  source: $coords.map(({ x }) => x),
  target: setX,
  key: 'x',
})

// persist Y coordinate in `localStorage` with key 'y'
persist({
  source: $coords.map(({ y }) => y),
  target: setY,
  key: 'y',
})

⚠️ BIG WARNING! Use this approach with caution, beware of infinite circular updates. To avoid them, persist only plain values in storage. So, mapped store in source will not trigger update, if object in original store has changed. Also, you can take a look at updateFilter option.