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https://github.com/LegendApp/legend-state

Legend-State is a super fast and powerful state library that enables fine-grained reactivity and easy automatic persistence
https://github.com/LegendApp/legend-state

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Legend-State is a super fast and powerful state library that enables fine-grained reactivity and easy automatic persistence

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README 

        
# Legend-State



Legend-State is a super fast all-in-one state and sync library that lets you write less code to make faster apps. Legend-State has four primary goals:



### 1. 🦄 As easy as possible to use



There is no boilerplate and there are no contexts, actions, reducers, dispatchers, sagas, thunks, or epics. It doesn't modify your data at all, and you can just call `get()` to get the raw data and `set()` to change it.



In React components you can call `use()` on any observable to get the raw data and automatically re-render whenever it changes.



```jsx

import { observable, observe } from "@legendapp/state"

import { observer } from "@legendapp/state/react"



const settings$ = observable({ theme: 'dark' })



// get returns the raw data

settings$.theme.get() // 'dark'

// set sets

settings$.theme.set('light')



// Computed observables with just a function

const isDark$ = observable(() => settings$.theme.get() === 'dark')



// observing contexts re-run when tracked observables change

observe(() => {

  console.log(settings$.theme.get())

})



const Component = observer(function Component() {

    const theme = state$.settings.theme.get()



    return 
Theme: {theme}


})

```



### 2. ⚡️ The fastest React state library



Legend-State beats every other state library on just about every metric and is so optimized for arrays that it even beats vanilla JS on the "swap" and "replace all rows" benchmarks. At only `4kb` and with the massive reduction in boilerplate code, you'll have big savings in file size too.





    




See [Fast 🔥](https://www.legendapp.com/open-source/state/v3/intro/fast/) for more details of why Legend-State is so fast.



### 3. 🔥 Fine-grained reactivity for minimal renders



Legend-State lets you make your renders super fine-grained, so your apps will be much faster because React has to do less work. The best way to be fast is to render less, less often.



```jsx

function FineGrained() {

    const count$ = useObservable(0)



    useInterval(() => {

        count$.set(v => v + 1)

    }, 600)



    // The text updates itself so the component doesn't re-render

    return (

        


            Count: {count$}

        


    )

}

```



### 4. 💾 Powerful sync and persistence



Legend-State includes a powerful [sync and persistence system](../../usage/persist-sync). It easily enables local-first apps by optimistically applying all changes locally first, retrying changes even after restart until they eventually sync, and syncing minimal diffs. We use Legend-State as the sync systems in [Legend](https://legendapp.com) and [Bravely](https://bravely.io), so it is by necessity very full featured while being simple to set up.



Local persistence plugins for the browser and React Native are included, with sync plugins for [Keel](https://www.keel.so), [Supabase](https://www.supabase.com), [TanStack Query](https://tanstack.com/query), and `fetch`.



```js

const state$ = observable(

    users: syncedKeel({

        list: queries.getUsers,

        create: mutations.createUsers,

        update: mutations.updateUsers,

        delete: mutations.deleteUsers,

        persist: { name: 'users', retrySync: true },

        debounceSet: 500,

        retry: {

            infinite: true,

        },

        changesSince: 'last-sync',

    }),

    // direct link to my user within the users observable

    me: () => state$.users['myuid']

)



observe(() => {

    // get() activates through to state$.users and starts syncing.

    // it updates itself and re-runs observers when name changes

    const name = me$.name.get()

})



// Setting a value goes through to state$.users and saves update to server

me$.name.set('Annyong')

```



## Install



`bun add @legendapp/state` or `npm install @legendapp/state` or `yarn add @legendapp/state`



## Highlights



- ✨ Super easy to use 😌

- ✨ Super fast ⚡️

- ✨ Super small at 4kb 🐥

- ✨ Fine-grained reactivity 🔥

- ✨ No boilerplate

- ✨ Designed for maximum performance and scalability

- ✨ React components re-render only on changes

- ✨ Very strongly typed with TypeScript

- ✨ Persistence plugins for automatically saving/loading from storage

- ✨ State can be global or within components



[Read more](https://www.legendapp.com/open-source/state/v3/intro/why/) about why Legend-State might be right for you.



## Documentation



See [the documentation site](https://www.legendapp.com/open-source/state/).



## Community



Join us on [Discord](https://discord.gg/5CBaNtADNX) to get involved with the Legend community.



## 👩‍⚖️ License



[MIT](LICENSE)



---



Legend-State is created and maintained by [Jay Meistrich](https://github.com/jmeistrich) with [Legend](https://www.legendapp.com) and [Bravely](https://www.bravely.io).





    Legend

        

    Bravely