visit jotai.org or npm i 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)
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.
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 })It can be used like React.useState:
import { useAtom } from 'jotai'
function Counter() {
const [count, setCount] = useAtom(countAtom)
return (
<h1>
{count}
<button onClick={() => setCount((c) => c + 1)}>one up</button>
...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.
const doubledCountAtom = atom((get) => get(countAtom) * 2)
function DoubleCounter() {
const [doubledCount] = useAtom(doubledCountAtom)
return <h2>{doubledCount}</h2>
}You can combine multiple atoms to create a derived atom.
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 ...
const atoms = [count1, count2, count3, ...otherAtoms]
const sum = atom((get) => atoms.map(get).reduce((acc, count) => acc + count))
You can make the read function an async function too.
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)
...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.
const decrementCountAtom = atom(
(get) => get(countAtom),
(get, set, _arg) => set(countAtom, get(countAtom) - 1)
)
function Counter() {
const [count, decrement] = useAtom(decrementCountAtom)
return (
<h1>
{count}
<button onClick={decrement}>Decrease</button>
...Just do not define a read function.
const multiplyCountAtom = atom(null, (get, set, by) =>
set(countAtom, get(countAtom) * by),
)
function Controls() {
const [, multiply] = useAtom(multiplyCountAtom)
return <button onClick={() => multiply(3)}>triple</button>
}Just make the write function an async function and call set when you're ready.
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 (
<button onClick={() => compute('http://count.host.com')}>compute</button>
...Jotai's fluid interface is no accident — atoms are monads, just like promises! Monads are an established pattern for modular, pure, robust and understandable code which is optimized for change. Read more about Jotai and monads.
