Nano Stores

A tiny state manager for React, React Native, Preact, Vue, Svelte, Solid, Lit, Angular, and vanilla JS. It uses many atomic stores and direct manipulation.

• Small. Between 265 and 803 bytes (minified and brotlied). Zero dependencies. It uses Size Limit to control size.
• Fast. With small atomic and derived stores, you do not need to call the selector function for all components on every store change.
• Tree Shakable. A chunk contains only stores used by components in the chunk.
• Designed to move logic from components to stores.
• Good TypeScript support.

// store/users.ts
import { atom } from 'nanostores'

export const $users = atom<User[]>([])

export function addUser(user: User) {
  $users.set([...$users.get(), user]);
}

// store/admins.ts
import { computed } from 'nanostores'
import { $users } from './users.js'

export const $admins = computed($users, users => users.filter(i => i.isAdmin))

// components/admins.tsx
import { useStore } from '@nanostores/react'
import { $admins } from '../stores/admins.js'

export const Admins = () => {
  const admins = useStore($admins)
  return (
    <ul>
      {admins.map(user => <UserItem user={user} />)}
    </ul>
  )
}

  Made at Evil Martians, product consulting for developer tools.

• Table of Contents
• Install
• Smart Stores
• Devtools
• Guide
  • Atoms
  • Maps
  • Deep Maps
  • Lazy Stores
  • Computed Stores
  • Tasks
  • Store Events
• Integration
  • React & Preact
  • Vue
  • Svelte
  • Solid
  • Lit
  • Angular
  • Vanilla JS
  • Server-Side Rendering
  • Tests
• Best Practices
  • Move Logic from Components to Stores
  • Separate changes and reaction
  • Reduce get() usage outside of tests
• Known Issues
  • ESM

npm install nanostores

• Persistent store to save data to localStorage and synchronize changes between browser tabs.
• Router store to parse URL and implements SPA navigation.
• I18n library based on stores to make application translatable.
• Query store that helps you with smart remote data fetching.
• Logux Client: stores with WebSocket sync and CRDT conflict resolution.

• Logger of lifecycles, changes in the browser console.
• Vue Devtools plugin that detects stores and attaches them to devtools inspectors and timeline.

Atom store can be used to store strings, numbers, arrays.

You can use it for objects too if you want to prohibit key changes and allow only replacing the whole object (like we do in router).

To create it call atom(initial) and pass initial value as a first argument.

import { atom } from 'nanostores'

export const $counter = atom(0)

In TypeScript, you can optionally pass value type as type parameter.

export type LoadingStateValue = 'empty' | 'loading' | 'loaded'

export const $loadingState = atom<LoadingStateValue>('empty')

Then you can use StoreValue<Store> helper to get store’s value type in TypeScript:

import type { StoreValue } from 'nanostores'

type Value = StoreValue<typeof $loadingState> //=> LoadingStateValue

store.get() will return store’s current value. store.set(nextValue) will change value.

$counter.set($counter.get() + 1)

store.subscribe(cb) and store.listen(cb) can be used to subscribe for the changes in vanilla JS. For React/Vue we have extra special helpers useStore to re-render the component on any store changes.

Listener callbacks will receive the updated value as a first argument and the previous value as a second argument.

const unbindListener = $counter.subscribe((value, oldValue) => {
  console.log(`counter value changed from ${oldValue} to ${value}`)
})

store.subscribe(cb) in contrast with store.listen(cb) also call listeners immediately during the subscription. Note that the initial call for store.subscribe(cb) will not have any previous value and oldValue will be undefined.

Map store can be used to store objects with one level of depth and change keys in this object.

To create map store call map(initial) function with initial object.

import { map } from 'nanostores'

export const $profile = map({
  name: 'anonymous'
})

In TypeScript you can pass type parameter with store’s type:

export interface ProfileValue {
  name: string,
  email?: string
}

export const $profile = map<ProfileValue>({
  name: 'anonymous'
})

store.set(object) or store.setKey(key, value) methods will change the store.

$profile.setKey('name', 'Kazimir Malevich')

Setting undefined will remove optional key:

$profile.setKey('email', undefined)

Store’s listeners will receive third argument with changed key.

$profile.listen((profile, oldProfile, changed) => {
  console.log(`${changed} new value ${profile[changed]}`)
})

You can also listen for specific keys of the store being changed, using listenKeys and subscribeKeys.

listenKeys($profile, ['name'], (value, oldValue, changed) => {
  console.log(`$profile.Name new value ${value.name}`)
})

subscribeKeys(store, keys, cb) in contrast with listenKeys(store, keys, cb) also call listeners immediately during the subscription. Please note that when using subscribe for store changes, the initial evaluation of the callback has undefined old value and changed key.

Deep maps work the same as map, but it supports arbitrary nesting of objects and arrays that preserve the fine-grained reactivity.

import { deepMap, listenKeys } from 'nanostores'

export const $profile = deepMap({
  hobbies: [
    {
      name: 'woodworking',
      friends: [{ id: 123, name: 'Ron Swanson' }]
    }
  ],
  skills: [
    [
      'Carpentry',
      'Sanding'
    ],
    [
      'Varnishing'
    ]
  ]
})

listenKeys($profile, ['hobbies[0].friends[0].name', 'skills[0][0]'])

// Won't fire subscription
$profile.setKey('hobbies[0].name', 'Scrapbooking')
$profile.setKey('skills[0][1]', 'Staining')

// But those will fire subscription
$profile.setKey('hobbies[0].friends[0].name', 'Leslie Knope')
$profile.setKey('skills[0][0]', 'Whittling')

Note that setKey creates copies as necessary so that no part of the original object is mutated (but it does not do a full deep copy -- some sub-objects may still be shared between the old value and the new one).

A unique feature of Nano Stores is that every state has two modes:

• Mount: when one or more listeners is mounted to the store.
• Disabled: when store has no listeners.

Nano Stores was created to move logic from components to the store. Stores can listen for URL changes or establish network connections. Mount/disabled modes allow you to create lazy stores, which will use resources only if store is really used in the UI.

onMount sets callback for mount and disabled states.

import { onMount } from 'nanostores'

onMount($profile, () => {
  // Mount mode
  return () => {
    // Disabled mode
  }
})

For performance reasons, store will move to disabled mode with 1 second delay after last listener unsubscribing.

Call keepMount() to test store’s lazy initializer in tests and cleanStores to unmount them after test.

import { cleanStores, keepMount } from 'nanostores'
import { $profile } from './profile.js'

afterEach(() => {
  cleanStores($profile)
})

it('is anonymous from the beginning', () => {
  keepMount($profile)
  // Checks
})

Computed store is based on other store’s value.

import { computed } from 'nanostores'
import { $users } from './users.js'

export const $admins = computed($users, users => {
  // This callback will be called on every `users` changes
  return users.filter(user => user.isAdmin)
})

An async function can be evaluated by using task().

import { computed, task } from 'nanostores'

import { $userId } from './users.js'

export const $user = computed($userId, userId => task(async () => {
  const response = await fetch(`https://my-api/users/${userId}`)
  return response.json()
}))

By default, computed stores update each time any of their dependencies gets updated. If you are fine with waiting until the end of a tick, you can use batched. The only difference with computed is that it will wait until the end of a tick to update itself.

import { batched } from 'nanostores'

const $sortBy = atom('id')
const $categoryId = atom('')

export const $link = batched([$sortBy, $categoryId], (sortBy, categoryId) => {
  return `/api/entities?sortBy=${sortBy}&categoryId=${categoryId}`
})

// `batched` will update only once even you changed two stores
export function resetFilters () {
  $sortBy.set('date')
  $categoryIdFilter.set('1')
}

Both computed and batched can be calculated from multiple stores:

import { $lastVisit } from './lastVisit.js'
import { $posts } from './posts.js'

export const $newPosts = computed([$lastVisit, $posts], (lastVisit, posts) => {
  return posts.filter(post => post.publishedAt > lastVisit)
})

startTask() and task() can be used to mark all async operations during store initialization.

import { task } from 'nanostores'

onMount($post, () => {
  task(async () => {
    $post.set(await loadPost())
  })
})

You can wait for all ongoing tasks end in tests or SSR with await allTasks().

import { allTasks } from 'nanostores'

$post.listen(() => {}) // Move store to active mode to start data loading
await allTasks()

const html = ReactDOMServer.renderToString(<App />)

Each store has a few events, which you listen:

• onMount(store, cb): first listener was subscribed with debounce. We recommend to always use onMount instead of onStart + onStop, because it has a short delay to prevent flickering behavior.
• onStart(store, cb): first listener was subscribed. Low-level method. It is better to use onMount for simple lazy stores.
• onStop(store, cb): last listener was unsubscribed. Low-level method. It is better to use onMount for simple lazy stores.
• onSet(store, cb): before applying any changes to the store.
• onNotify(store, cb): before notifying store’s listeners about changes.

onSet and onNotify events has abort() function to prevent changes or notification.

import { onSet } from 'nanostores'

onSet($store, ({ newValue, abort }) => {
  if (!validate(newValue)) {
    abort()
  }
})

Event listeners can communicate with payload.shared object.

Use @nanostores/react or @nanostores/preact package and useStore() hook to get store’s value and re-render component on store’s changes.

import { useStore } from '@nanostores/react' // or '@nanostores/preact'
import { $profile } from '../stores/profile.js'

export const Header = ({ postId }) => {
  const profile = useStore($profile)
  return <header>Hi, {profile.name}</header>
}

Use @nanostores/vue and useStore() composable function to get store’s value and re-render component on store’s changes.

<script setup>
import { useStore } from '@nanostores/vue'
import { $profile } from '../stores/profile.js'

const props = defineProps(['postId'])

const profile = useStore($profile)
</script>

<template>
  <header>Hi, {{ profile.name }}</header>
</template>

Every store implements Svelte's store contract. Put $ before store variable to get store’s value and subscribe for store’s changes.

<script>
  import { profile } from '../stores/profile.js'
</script>

<header>Hi, {$profile.name}</header>

In other frameworks, Nano Stores promote code style to use $ prefixes for store’s names. But in Svelte it has a special meaning, so we recommend to not follow this code style here.

Use @nanostores/solid and useStore() composable function to get store’s value and re-render component on store’s changes.

import { useStore } from '@nanostores/solid'
import { $profile } from '../stores/profile.js'

export function Header({ postId }) {
  const profile = useStore($profile)
  return <header>Hi, {profile().name}</header>
}

Use @nanostores/lit and StoreController reactive controller to get store’s value and re-render component on store’s changes.

import { StoreController } from '@nanostores/lit'
import { $profile } from '../stores/profile.js'

@customElement('my-header')
class MyElement extends LitElement {
  @property()

  private profileController = new StoreController(this, $profile)

  render() {
    return html\`<header>Hi, ${profileController.value.name}</header>`
  }
}

Use @nanostores/angular and NanostoresService with useStore() method to get store’s value and subscribe for store’s changes.

// NgModule:
import { NANOSTORES, NanostoresService } from '@nanostores/angular';

@NgModule({
  providers: [{ provide: NANOSTORES, useClass: NanostoresService }]
})

// Component:
import { Component } from '@angular/core'
import { NanostoresService } from '@nanostores/angular'
import { Observable, switchMap } from 'rxjs'

import { profile } from '../stores/profile'
import { IUser, User } from '../stores/user'

@Component({
  selector: "app-root",
  template: '<p *ngIf="(currentUser$ | async) as user">{{ user.name }}</p>'
})
export class AppComponent {
  currentUser$: Observable<IUser> = this.nanostores.useStore(profile)
    .pipe(switchMap(userId => this.nanostores.useStore(User(userId))))

  constructor(private nanostores: NanostoresService) { }
}

Store#subscribe() calls callback immediately and subscribes to store changes. It passes store’s value to callback.

import { $profile } from '../stores/profile.js'

$profile.subscribe(profile => {
  console.log(`Hi, ${profile.name}`)
})

Store#listen(cb) in contrast calls only on next store change. It could be useful for a multiple stores listeners.

function render () {
  console.log(`${$post.get().title} for ${$profile.get().name}`)
}

$profile.listen(render)
$post.listen(render)
render()

See also listenKeys(store, keys, cb) to listen for specific keys changes in the map.

Nano Stores support SSR. Use standard strategies.

if (isServer) {
  $settings.set(initialSettings)
  $router.open(renderingPageURL)
}

You can wait for async operations (for instance, data loading via isomorphic fetch()) before rendering the page:

import { allTasks } from 'nanostores'

$post.listen(() => {}) // Move store to active mode to start data loading
await allTasks()

const html = ReactDOMServer.renderToString(<App />)

Adding an empty listener by keepMount(store) keeps the store in active mode during the test. cleanStores(store1, store2, …) cleans stores used in the test.

import { cleanStores, keepMount } from 'nanostores'
import { $profile } from './profile.js'

afterEach(() => {
  cleanStores($profile)
})

it('is anonymous from the beginning', () => {
  keepMount($profile)
  expect($profile.get()).toEqual({ name: 'anonymous' })
})

You can use allTasks() to wait all async operations in stores.

import { allTasks } from 'nanostores'

it('saves user', async () => {
  saveUser()
  await allTasks()
  expect(analyticsEvents.get()).toEqual(['user:save'])
})

Stores are not only to keep values. You can use them to track time, to load data from server.

import { atom, onMount } from 'nanostores'

export const $currentTime = atom<number>(Date.now())

onMount($currentTime, () => {
  $currentTime.set(Date.now())
  const updating = setInterval(() => {
    $currentTime.set(Date.now())
  }, 1000)
  return () => {
    clearInterval(updating)
  }
})

Use derived stores to create chains of reactive computations.

import { computed } from 'nanostores'
import { $currentTime } from './currentTime.js'

const appStarted = Date.now()

export const $userInApp = computed($currentTime, currentTime => {
  return currentTime - appStarted
})

We recommend moving all logic, which is not highly related to UI, to the stores. Let your stores track URL routing, validation, sending data to a server.

With application logic in the stores, it is much easier to write and run tests. It is also easy to change your UI framework. For instance, add React Native version of the application.

Use a separated listener to react on new store’s value, not an action function where you change this store.

  function increase() {
    $counter.set($counter.get() + 1)
-   printCounter(store.get())
  }

+ $counter.listen(counter => {
+   printCounter(counter)
+ })

An action function is not the only way for store to a get new value. For instance, persistent store could get the new value from another browser tab.

With this separation your UI will be ready to any source of store’s changes.

get() returns current value and it is a good solution for tests.

But it is better to use useStore(), $store, or Store#subscribe() in UI to subscribe to store changes and always render the actual data.

- const { userId } = $profile.get()
+ const { userId } = useStore($profile)

Nano Stores use ESM-only package. You need to use ES modules in your application to import Nano Stores.

In Next.js ≥11.1 you can alternatively use the esmExternals config option.

For old Next.js you need to use next-transpile-modules to fix lack of ESM support in Next.js.