visit [jotai.org](https://jotai.org) or `npm i jotai`
[](https://github.com/pmndrs/jotai/actions?query=workflow%3ALint)
[](https://bundlephobia.com/result?p=jotai)
[](https://www.npmjs.com/package/jotai)
[](https://www.npmjs.com/package/jotai)
[](https://discord.gg/poimandres)
[](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)
](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 (