0.1.2 • Public • Published


    ReScript bindings for Jotai. Primitive and flexible state management for React.


    Install with npm:

    npm install jotai @fattafatta/rescript-jotai

    Or install with yarn:

    yarn add jotai @fattafatta/rescript-jotai

    Add @fattafatta/rescript-jotai as a dependency to your bsconfig.json:

    "bs-dependencies": ["@rescript/react", "@fattafatta/rescript-jotai"]



    A Provider works just like React context provider. If you don't use a Provider, it works as provider-less mode with a default store. A Provider will be necessary if we need to hold different atom values for different component trees.

    module App = {
      let make = () =>

    Create atoms

    Atom type

    Atoms have a value, a setter function (from Atom.Actions), and a set of tags that restrict which operations are allowed on the atom (e.g is the atom #resettable). Normally the type will be inferred automatically. If annotation is required it should be sufficient to provide the first type (the value).


    let atom: Jotai.Atom.t<int, _, _> = Jotai.Atom.make(1)

    Primitive atom (Jotai.Atom.make)

    Create a (primitive) readable and writable atom.

    let atom1 = Jotai.Atom.make(1)
    let atom2 = Jotai.Atom.make('text')

    Computed atom (Jotai.Atom.makeComputed)

    Create a computed readonly atom. A computed atom can combine any number of readable atoms to create a single derived value. The syntax varies slightly from Jotai. Note the curly braces in ({get}).

    let atom1 = Jotai.Atom.make(1)
    let atom2 = Jotai.Atom.makeComputed(({get}) => get(atom1) + 1)
    let atom3 = Jotai.Atom.makeComputed(({get}) => get(atom1) + get(atom2) + 1)

    Computed async atom (Jotai.Atom.makeComputedAsync)

    (Requires React.Suspense) Create an computed readonly atom with an async getter. All components will be notified when the returned promise resolves.

    let atom1 = Jotai.Atom.make(1)
    let atom2 = Jotai.Atom.makeComputedAsync(({get}) => {
      Js.Promise.make((~resolve, ~reject as _) => {
        let count = atom1->get + 1
        Js.Global.setTimeout(() => resolve(. count), 100)->ignore

    Computed writable atom (Jotai.Atom.makeWritableComputed)

    Create a computed atom that supports read and write.

    let atom1 = Jotai.Atom.make(1)
    let atom2 = Jotai.Atom.makeWritableComputed(
      ({get}) => get(atom1) + 1,
      ({get, set}, arg) => {
        atom1->set(get(atom1) + arg)

    Computed writable async atom (Jotai.Atom.makeWritableComputedAsync)

    Create a computed atom with asynchronous write. Jotai supports async write operations for computed atoms. Simply call 'set' when the promise resolves.

    let atom1 = Jotai.Atom.make(1)
    let atom2 = Jotai.Atom.makeWritableComputedAsync(
      ({get}) => get(atom1) + 1,
      ({get, set}, arg) => {
        Js.Promise.make((~resolve, ~reject as _) => {
          let count = get(atom1) + arg
          Js.Global.setTimeout(() => resolve(. count), 100)->ignore
        })->Js.Promise.then_(value => {
        }, _)

    Computed writeonly atom (Jotai.Atom.makeWriteOnlyComputed)

    Create a writeOnly computed atom.(Note: Sometimes the type can not be inferred and has to be annotated)

    let atom1 = make(1)
    let atom2: Jotai.Atom.t<int, _, _> = Jotai.Atom.makeWriteOnlyComputed(({get, set}, args) =>
      atom1->set(get(atom1) + args)

    OnMount (Jotai.Atom.onMount)

    The onMount function will be invoked when the atom is first used in a provider, and onUnmount will be invoked when it's not used.

    let atom1 = Jotai.Atom.make(1)
    atom1->Jotai.Atom.onMount(setAtom => {
      setAtom(a => a + 1) // increment count on mount
      () => () // return onUnmount function

    Standard hook

    Using read/write atoms (Jotai.Atom.use)

    Standard hook to use with read/write atoms. (For handling of readOnly/writeOnly atoms see Jotai.Utils)

    let atom1 = Jotai.Atom.make(1)
    let (value, setValue) = Jotai.Atom.use(atom1)


    Atom with localStorage (Jotai.Utils.AtomWithStorage.make)

    Creates an atom with a value persisted in localStorage Currently only localStorage is supported.

    let atom1 = Jotai.Utils.AtomWithStorage.make('storageKey', 1)

    Resettable atom (Jotai.Utils.AtomWithReset.make)

    Creates an atom that can be resetted to its initialValue with the useResetAtom hook.

    let atom = Jotai.Utils.AtomWithReset.make(1)
    // ... change value ...
    let reset = Jotai.Utils.useResetAtom(atom)

    Atom with default (Jotai.Utils.AtomWithDefault.make)

    Create a resettable primitive atom. Its default value can be specified with a read function instead of a static initial value.

    let atom1 = Jotai.Atom.make(1)
    let atom2 = Jotai.Utils.AtomWithDefault.make(({get}) => atom1->get + 1)

    Atom with Reducer (Jotai.Utils.AtomWithReducer.make)

    Creates an atom that uses a reducer to update its value.

    type actionType = Inc(int) | Dec(int)
    let countReducer = (prev, action) => {
      switch action {
      | Inc(num) => prev + num
      | Dec(num) => prev - num
    let atom = Utils.AtomWithReducer.make(0, countReducer)
    let (value, dispatch) = Atom.use(atom)

    Utils Hooks

    Get only the update function (Jotai.Utils.useUpdateAtom)

    A hook that returns only the update function of an atom. Can be used to access writeOnly atoms.

    let atom = Jotai.Atom.make(1)
    let setValue = Jotai.Utils.useUpdateAtom(atom)
    setValue(prev => prev + 1)

    Get only the value (Jotai.Utils.useAtomValue)

    A hook that returns only the value of an atom. Can be used to access readOnly atoms.

    let atom = Jotai.Atom.make(1)
    let value = Jotai.Utils.useAtomValue(atom)

    Reset an atom (Jotai.Utils.useResetAtom)

    Returns a function that can be used to reset a resettable atom.

    let atom = Jotai.Utils.AtomWithReset(1)  // value: 1
    let (_, setValue) = Jotai.Atom.use(atom)
    setValue(2)  // value: 2
    let resetValue = Jotai.Utils.useResetAtom(atom)
    resetValue()  // value back to: 1

    Pass a reducer to a writable atom (Jotai.Utils.useReducerAtom)

    Allows to use a reducer function with a primitive atom.

    type actionType = Inc(int) | Dec(int)
    let countReducer = (prev, action) => {
      switch action {
      | Inc(num) => prev + num
      | Dec(num) => prev - num
    let atom = Jotai.Atom.make(0)
    let (value, dispatch) = Jotai.Utils.useReducerAtom(atom, countReducer)


    This package was greatly inspired by re-jotai. I just preferred to have a different syntax for the get/set functions.

    Missing functions from Jotai

    These functions are not (yet) supported.

    • atomWithObservable
    • atomWithHash
    • atomFamily
    • selectAtom
    • useAtomCallback
    • freezeAtom
    • splitAtom
    • waitForAll
    • useHydrateAtoms


    npm i @fattafatta/rescript-jotai

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