jotai

Primitive, flexible state management for React.

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

How does Jotai differ from Recoil?

  • Minimalistic API
  • No string keys
  • TypeScript oriented

doc.01

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 })

doc.02

You can only use atoms under this component tree.

import { Provider } from 'jotai'

const Root = () => (
  <Provider>
    <App />
  </Provider>
)

doc.03

It can be used just 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>

doc.04

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>

rec.00

rec.01

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))

rec.02

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 changed and the async function above concludes
  const [json] = useAtom(fetchUrlAtom)

rec.03

Specify a write function at the second argument. get will return the current value of an atom, set will update an atoms value.

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>

rec.04

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>

rec.05

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>

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