Jotai

Primitive and flexible state management for React

State management React

pmndrs/jotai jotai.org jotai

README

npm i jotai or visit jotai.org

Jotai is pronounced "joe-tie" and means "state" in Japanese.

You can try live demos in the following:

Demo 1 |

Demo 2.

How does Jotai differ from Recoil?

- Minimalistic API

- No string keys

- TypeScript oriented

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 (
<h1>
{count}
<button onClick={() => setCount(c => c + 1)}>one up</button>
```

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 <h2>{doubledCount}</h2>
```

Recipes

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

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 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 an atoms value.

```jsx
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>
```

Write only 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 <button onClick={() => multiply(3)}>triple</button>
```

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 <button onClick={() => compute("http://count.host.com")}>compute</button>
```

Installation notes

This package requires some peer dependencies, which you need to install by

yourself.

```bash
yarn add jotai react
```