Quick Tutorial

You can skip this part if you've already read the Github README.

xoid has only 4 exports: create, effect, subscribe, and use. This section will cover all of them, and the @xoid/react.

Atom

Atoms are standalone setter/getter objects that hold state. create function is used to create them.

import { create } from 'xoid'
const atom = create(3)
atom() // 3 (get the value)
atom(5) // void (set the value to 5)
atom(state => state + 1) // void (also set the value)
atom() // 6

Atoms can have actions, and with use function they can be used.

import { create, use } from 'xoid'
const numberAtom = create(5, (atom) => ({
increment: () => atom(s => s + 1),
decrement: () => atom(s => s - 1)
}))
use(numberAtom).increment()

use function, when used with a second argument, acts as a selector. The selected node will be a subscribable getter/setter object like any other atom. xoid is based on immutable updates, so if you "surgically" set state of a selected branch, changes will propagate to the root.

import { create, use } from 'xoid'
const atom = create({ deeply: { nested: { alpha: 5 } } })
const previousState = atom()
// select `.deeply.nested.alpha`
const alpha = use(atom, s => s.deeply.nested.alpha)
alpha(s => s + 1)
// root state is replaced with new immutable state
assert(atom() !== previousState) // ✅
assert(atom().deeply.nested.alpha === 6) // ✅

Derived state

Atoms can be derived from other atoms. This API was heavily inspired by Recoil.

import { create } from 'xoid'
const alpha = create(3)
const beta = create(5)
// derived atom
const sum = create((get) => get(alpha) + get(beta))

Subscriptions

For subscriptions, subscribe and effect are used. They are the same, except effect runs the callback immediately, while subscribe waits for the first update after subscription.

import { subscribe } from 'xoid'
const unsub = subscribe(
atom,
(state, previousState) => { console.log(state, previousState) }
)

To cleanup side-effects, a function can be returned in the subscriber function. (Just like React.useEffect)

React integration

@xoid/react is based on two hooks. useAtom subscribes the component to an atom. If a second argument is supplied, it'll be used as a selector function.

import { useAtom } from '@xoid/react'
// in a React component
const state = useAtom(atom, s => s.alpha)

The other hook is useSetup. It can be used for creating local component state. It'll run its closure only once. If a second argument is supplied, it'll be used for communication between the closure (useSetup scope) and outside (React component scope).

import { subscribe, use } from 'xoid'
import { useSetup } from '@xoid/react'
const App = (props: Props) => {
const setup = useSetup(($props) => {
// `$props` has the type: Atom<Props>
// this way, we can react to `props.something` as it changes
subscribe(use($props, s => s.something), console.log)
const alpha = create(5)
return { alpha }
}, props)
...
}

useSetup is guaranteed to be non-render-causing. Atoms returned by that should be explicitly subscribed via useAtom hook.

This is a

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