![Jotai (light mode)](./img/jotai-header-light.png#gh-light-mode-only)
visit [jotai.org](https://jotai.org) or `npm i jotai` [![Build Status](https://img.shields.io/github/actions/workflow/status/pmndrs/jotai/lint-and-type.yml?branch=main&style=flat&colorA=000000&colorB=000000)](https://github.com/pmndrs/jotai/actions?query=workflow%3ALint) [![Build Size](https://img.shields.io/bundlephobia/minzip/jotai?label=bundle%20size&style=flat&colorA=000000&colorB=000000)](https://bundlephobia.com/result?p=jotai) [![Version](https://img.shields.io/npm/v/jotai?style=flat&colorA=000000&colorB=000000)](https://www.npmjs.com/package/jotai) [![Downloads](https://img.shields.io/npm/dt/jotai.svg?style=flat&colorA=000000&colorB=000000)](https://www.npmjs.com/package/jotai) [![Discord Shield](https://img.shields.io/discord/740090768164651008?style=flat&colorA=000000&colorB=000000&label=discord&logo=discord&logoColor=ffffff)](https://discord.gg/poimandres) [![Open Collective](https://img.shields.io/opencollective/all/jotai?style=flat&colorA=000000&colorB=000000)](https://opencollective.com/jotai) Jotai scales from a simple useState replacement to an enterprise TypeScript application. - Minimal core API (2kb) - Many utilities and extensions - No string keys (compared to Recoil) Examples: [Demo 1](https://codesandbox.io/s/jotai-demo-47wvh) | [Demo 2](https://codesandbox.io/s/jotai-demo-forked-x2g5d) ### First, create a primitive atom An atom represents a piece of state. All you need is to specify an initial value, which can be primitive values like strings and numbers, objects, and arrays. You can create as many primitive atoms as you want. ```jsx import { atom } from 'jotai' const countAtom = atom(0) const countryAtom = atom('Japan') const citiesAtom = atom(['Tokyo', 'Kyoto', 'Osaka']) const mangaAtom = atom({ 'Dragon Ball': 1984, 'One Piece': 1997, Naruto: 1999 }) ``` ### Use the atom in your components It can be used like `React.useState`: ```jsx import { useAtom } from 'jotai' function Counter() { const [count, setCount] = useAtom(countAtom) return (

{count} ... ``` ### Create derived atoms with computed values A new read-only atom can be created from existing atoms by passing a read function as the first argument. `get` allows you to fetch the contextual value of any atom. ```jsx const doubledCountAtom = atom((get) => get(countAtom) * 2) function DoubleCounter() { const [doubledCount] = useAtom(doubledCountAtom) return

{doubledCount}

} ``` ### Creating an atom from multiple atoms You can combine multiple atoms to create a derived atom. ```jsx const count1 = atom(1) const count2 = atom(2) const count3 = atom(3) const sum = atom((get) => get(count1) + get(count2) + get(count3)) ``` Or if you like fp patterns ... ```jsx const atoms = [count1, count2, count3, ...otherAtoms] const sum = atom((get) => atoms.map(get).reduce((acc, count) => acc + count)) ``` ### Derived async atoms [

](https://react.dev/reference/react/Suspense) You can make the read function an async function too. ```jsx const urlAtom = atom('https://json.host.com') const fetchUrlAtom = atom(async (get) => { const response = await fetch(get(urlAtom)) return await response.json() }) function Status() { // Re-renders the component after urlAtom is changed and the async function above concludes const [json] = useAtom(fetchUrlAtom) ... ``` ### You can create a writable derived atom Specify a write function at the second argument. `get` will return the current value of an atom. `set` will update the value of an atom. ```jsx const decrementCountAtom = atom( (get) => get(countAtom), (get, set, _arg) => set(countAtom, get(countAtom) - 1) ) function Counter() { const [count, decrement] = useAtom(decrementCountAtom) return (

{count} ... ``` ### Write only derived atoms Just do not define a read function. ```jsx const multiplyCountAtom = atom(null, (get, set, by) => set(countAtom, get(countAtom) * by), ) function Controls() { const [, multiply] = useAtom(multiplyCountAtom) return } ``` ### Async actions Just make the write function an async function and call `set` when you're ready. ```jsx const fetchCountAtom = atom( (get) => get(countAtom), async (_get, set, url) => { const response = await fetch(url) set(countAtom, (await response.json()).count) } ) function Controls() { const [count, compute] = useAtom(fetchCountAtom) return ( ... ``` ## Links - [website](https://jotai.org) - [documentation](https://jotai.org/docs) - [course](https://egghead.io/courses/manage-application-state-with-jotai-atoms-2c3a29f0)

			Stars	Issues	Version	Updated	Created	Size
	jotai				2.8.0	23 days ago	4 years ago
	swr				2.2.5	3 months ago	6 years ago

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