Nano Stores

CommonJS mirror of nanostores

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

• Small. Between 266 and 969 bytes (minified and gzipped). 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. The chunk contains only stores used by components in the chunk.
• Was designed to move logic from components to stores.
• It has 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, list =>
  list.filter(user => user.isAdmin)
)

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

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

Table of Contents

• Tools
• Guide
• Integration
  • React & Preact
  • Vue
  • Svelte
  • Solid
  • Vanilla JS
  • Server-Side Rendering
  • Tests
• Best Practices
• Known Issues

Install

npm install nanostores

Tools

• 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.
• Logux Client: stores with WebSocket sync and CRDT conflict resolution.

Guide

Atoms

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')

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 to re-render the component on any store changes.

const unbindListener = counter.subscribe(value => {
  console.log('counter value:', value)
})

store.subscribe(cb) in contrast with store.listen(cb) also call listeners immediately during the subscription.

Maps

Map store can be used to store objects 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')

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

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

You can use store.notify() to trigger listeners without changing value in the key for performance reasons.

store.get().bigList.push(newItem)
store.notify('bigList')

Maps Templates

Map templates was created for similar stores like for the store for each post in the blog where you have many posts. It is like class in ORM frameworks.

This is advanced tool, which could be too complicated to be used on every case. But it will be very useful for creating libraries like react-query. See Logux Client for example.

Nano Stores has map templates, to use a separated store for each item because of:

1. Performance: components can subscribe to the changes on specific post.
2. Lists can’t reflect that only specific subset of posts was loaded from the server.

mapTemplate(init) creates template. init callback will receive item’s store and ID.

import { mapTemplate } from 'nanostores'

export interface PostValue {
  id: string
  title: string
  updatedAt: number
}

export const Post = mapTemplate<PostValue>((newPost, id) => {
  newPost.setKey('title', 'New post')
  newPost.setKey('updatedAt', Date.now())
})

Each item of the template must have value.id.

let post1 = Post('1')
post1.get().id //=> '1'

Lazy Stores

Nano Stores unique feature is that every state have 2 modes:

• Mount: when one or more listeners was mount to the store.
• Disabled: when store has no listeners.

Nano Stores was created to move logic from components to the store. Stores can listen 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.

Map templates can use init callback for code for mount and disabled modes:

mapTemplate((post, id) => {
  // Mount mode
  let unsubscribe = loadDataAndSubscribe(`/posts/${id}`, data => {
    post.set(data)
  })
  return () => {
    // Disabled mode
    unsubscribe()
  }
})

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

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

afterEach(() => {
  cleanStores(Post)
})

it('is anonymous from the beginning', () => {
  let post = Post(1)
  keepMount(post)
  // Checks
})

Map template will keep cache of all mount stores:

postA = Post('same ID')
postB = Post('same ID')
postA === postB //=> true

Computed Stores

Computed store is based on other store’s value.

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

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

You can combine a value from multiple stores:

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

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

Actions

Action is a function that changes a store. It is a good place to move business logic like validation or network operations.

Wrapping functions with action() can track who changed the store in the logger.

import { action } from 'nanostores'

export const increase = action(counter, 'increase', (store, add) => {
  if (validateMax(store.get() + add)) {
    store.set(store.get() + add)
  }
  return store.get()
})

increase(1) //=> 1
increase(5) //=> 6

Actions for map template can be created with actionFor():

import { actionFor } from 'nanostores'

export const rename = actionFor(Post, 'rename', async (store, newTitle) => {
  await api.updatePost({
    id: store.get().id,
    title: newTitle
  })
  store.setKey('title', newTitle)
  store.setKey('updatedAt', Date.now())
})

await rename(post, 'New title')

All running async actions are tracked by allTasks(). It can simplify tests with chains of actions.

import { allTasks } from 'nanostores'

renameAllPosts()
await allTasks()

Tasks

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 />)

Async actions will be wrapped to task() automatically.

rename(post1, 'New title')
rename(post2, 'New title')
await allTasks()

Store Events

Each store has a few events, which you listen:

• onStart(store, cb): first listener was subscribed.
• onStop(store, cb): last listener was unsubscribed.
• onMount(store, cb): shortcut to use both onStart and onStop. We recommend to always use onMount instead of onStart + onStop, because it has a short delay to prevent flickering behavior.
• 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()
  }
})

Same event listeners can communicate with payload.shared object.

Integration

React & Preact

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'
import { Post } from '../stores/post.js'

export const Header = ({ postId }) => {
  const user = useStore(profile)
  const post = useStore(Post(postId))
  return <header>{post.title} for {user.name}</header>
}

Vue

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

<template>
  <header>{{ post.title }} for {{ user.name }}</header>
</template>

<script>
  import { useStore } from '@nanostores/vue'

  import { profile } from '../stores/profile.js'
  import { Post } from '../stores/post.js'

  export default {
    setup (props) {
      const user = useStore(profile)
      const post = useStore(Post(props.postId))
      return { user, post }
    }
  }
</script>

Svelte

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'
  import { Post } from '../stores/post.js'

  export let postId

  const post = Post(postId)
</script>

<header>{$post.title} for {$profile.name}</header>

Solid

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'
import { Post } from '../stores/post.js'

export function Header({ postId }) {
  const user = useStore(profile)
  const post = useStore(Post(postId))
  return <header>{post().title} for {user().name}</header>
}

Vanilla JS

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

import { profile } from '../stores/profile.js'
import { Post } from '../stores/post.js'

const post = Post(postId)

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

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

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

Server-Side Rendering

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 />)

Tests

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'])
})

Best Practices

Move Logic from Components to Stores

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, now => {
  return now - 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.

Separate changes and reaction

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

  const increase = action(counter, 'increase', store => {
    store.set(store.get() + 1)
-   printCounter(store.get())
  }

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

An action 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.

Reduce get() usage outside of tests

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)

Known Issues

ESM

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.