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Reatom

npm-react

Adapter for react↗.

Installation

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Terminal window
npm i @reatom/npm-react

Also, you need to be installed @reatom/core or @reatom/framework and react.

Read the core docs first for production usage.

Use atom

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reatomComponent

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The main API to bind atoms and actions to a component lifetime is reatomComponent. It wraps your regular react component and put ctx into the props. There is no additional rules or behavior, you can use any other hooks, accept props, return any valid ReactNode. But if you using ctx.spy, just like in any computed atom, it will subscribe to the passed atom and rerender from by changes.

import { atom } from '@reatom/core'
import { reatomComponent } from '@reatom/npm-react'


export const countAtom = atom(0)
export const Counter = reatomComponent(
  ({ ctx }) => (
    <input
      type="number"
      value={ctx.spy(count)}
      onChange={(e) => countAtom(ctx, e.target.valueAsNumber)}
    />
  ),
  'Counter',
)

You can describe props types in the generic, it can be any kind of values, regular string, JSON, and atoms too. For example, here is a controlled component with atom state.

import { atom, Atom } from '@reatom/core'
import { reatomComponent } from '@reatom/npm-react'


export const Counter = reatomComponent<{
  atom: Atom<number>
  onChange: Action
}>(
  ({ ctx, atom, onChange }) => (
    <input type="number" value={ctx.spy(atom)} onChange={ctx.bind(onChange)} />
  ),
  'Counter',
)

One of the most powerful features of reatomComponent is that you are not bound by react hooks rules, you could use ctx.spy in any order, right in your template.

export const SomeList = reatomComponent(
  ({ ctx }) =>
    ctx.spy(isLoadingAtom) ? (
      <span>Loading...</span>
    ) : (
      <ul>
        {ctx.spy(listAtom).map((el) => (
          <li>{el.text}</li>
        ))}
      </ul>
    ),
  'SomeList',
)

Do not forget to put the component name to the second argument, it will increase your feature debug experience a lot!

useAtom

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useAtom is your main hook, when you need to describe reusable logic in hight order hook. It accepts an atom to read it value and subscribes to the changes, or a primitive value to create a new mutable atom and subscribe to it. It alike useState, but with many additional features. It returns a tuple of [state, setState, theAtom, ctx]. theAtom is a reference to the passed or created atom.

In a component:

import { action, atom } from '@reatom/core'
import { useAction, useAtom } from '@reatom/npm-react'


// base mutable atom
const inputAtom = atom('', 'inputAtom')
// computed readonly atom
const greetingAtom = atom(
  (ctx) => `Hello, ${ctx.spy(inputAtom)}!`,
  'greetingAtom',
)
// action to do things
const onChange = action(
  (ctx, event: React.ChangeEvent<HTMLInputElement>) =>
    inputAtom(ctx, event.currentTarget.value),
  'onChange',
)


export const Greeting = () => {
  const [input] = useAtom(inputAtom)
  const [greeting] = useAtom(greetingAtom)
  const handleChange = useAction(onChange)


  return (
    <>
      <input value={input} onChange={handleChange} />
      {greeting}
    </>
  )
}

In the app root:

import { createCtx } from '@reatom/core'
import { reatomContext } from '@reatom/npm-react'


const ctx = createCtx()


export const App = () => (
  <reatomContext.Provider value={ctx}>
    <Main />
  </reatomContext.Provider>
)

We recommend to setup logger here.

Use atom selector

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Another use case for the hook is describing additional computations inside a component (create temporal computed atom). It is possible to put a reducer function to useState, which will create a new computed atom (setState will be undefined in this case).

import { useAtom } from '@reatom/npm-react'
import { goodsAtom } from '~/goods/model'


export const GoodsItem = ({ idx }: { idx: number }) => {
  const [element] = useAtom((ctx) => ctx.spy(goodsAtom)[idx], [idx])


  return <some-jsx {...element} />
}

The reducer function is just the same as in atom function. You could spy a few other atoms. It will be called only when the dependencies change, so you could use conditions and Reatom will optimize your dependencies and subscribes only to the necessary atoms.

import { useAtom } from '@reatom/npm-react'
import { activeAtom, goodsAtom } from '~/goods/model'


export const GoodsItem = ({ idx }: { idx: number }) => {
  const [element] = useAtom(
    (ctx) => (ctx.spy(activeAtom) === idx ? ctx.spy(listAtom)[idx] : null),
    [idx],
  )


  if (!element) return null


  return <some-jsx {...element} />
}

Advanced usage

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Check this out!

export const Greeting = ({ initialGreeting = '' }) => {
  const [input, setInput, inputAtom] = useAtom(initialGreeting)
  const [greeting] = useAtom(
    (ctx) => `Hello, ${ctx.spy(inputAtom)}!`,
    [inputAtom],
  )
  // you could do this
  const handleChange = useCallback(
    (event) => setInput(event.currentTarget.value),
    [setInput],
  )
  // OR this
  const handleChange = useAction(
    (ctx, event) => inputAtom(ctx, event.currentTarget.value),
    [inputAtom],
  )


  return (
    <>
      <input value={input} onChange={handleChange} />
      {greeting}
    </>
  )
}

What, why? In the example bellow we creating “inline” atoms, which will live only during the component lifetime. Here are the benefits of this pattern instead of using regular hooks:

  • You could depend your atoms by a props (deps changing will cause the callback rerun, the atom will the same).
  • Easy access to services, in case you use reatom as a DI.
  • Component inline atoms could be used for other computations, which could prevent rerenders (see above).
  • Created actions and atoms will be visible in logger / debugger with async cause tracking, which is much better for debugging than useEffect.
  • Unify codestyle for any state (local and global) description.
  • Easy to refactor to global state.

Lazy reading

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As react docs says↗, sometimes you need a callback, which depends on often changed value, but you don’t want to change a reference of this handler, to not broke memoization of children components which depends on the current. In this case, you could use atom and read it value lazily.

Here is a standard react code, handleSubmit reference is recreating on each input change and rerender.

const [input, setInput] = useState('')
const handleSubmit = useCallback(
  () => props.onSubmit(input),
  [props.onSubmit, input],
)

Here handleSubmit reference is stable and doesn’t depend on input, but have access to it last value.

const [input, setInput, inputAtom, ctx] = useAtom('')
const handleSubmit = useCallback(
  () => props.onSubmit(ctx.get(inputAtom)),
  [props.onSubmit, inputAtom, ctx],
)

Btw, you could use useAction.

const [input, setInput, inputAtom] = useAtom('')
const handleSubmit = useAction(
  (ctx) => props.onChange(ctx.get(inputAtom)),
  [props.onChange, inputAtom],
)

Prevent rerenders

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useAtom accepts third argument shouldSubscribe which is true by default. But sometimes you have a set of computations not all of which you need in the render. In this case you could use atoms from useAtom without subscribing to it values.

Here is how could you share data created and managed in parent, but used in children.

const [filter, setFilter, filterAtom] = useAtom('', [], false)
const [data, setData, dataAtom] = useAtom([], [], false)
const handleSubmit = useAction(
  (ctx) =>
    ctx.schedule(() =>
      fetch(`api/search?q=${ctx.get(filterAtom)}`)
        .then((res) => res.json())
        .then(setData),
    ),
  [filterAtom, dataAtom],
)


return (
  <>
    <Filter atom={filterAtom} />
    <Table atom={dataAtom} />
    {/* this will not rerender by filters or data changes */}
    <OtherComponent />
  </>
)

Here is another example of in-render computations which could be archived without rerender.

codesandbox

// this component will not rerender by `inputAtom` change, only by `numbers` change
const [, , inputAtom] = useAtom('', [], false)
const handleChange = useAction(
  (ctx, event) => inputAtom(ctx, event.currentTarget.value),
  [inputAtom],
)
const [numbers] = useAtom(
  (ctx) => ctx.spy(inputAtom).replace(/\D/g, ''),
  [inputAtom],
)


return (
  <>
    <input onChange={handleChange} />
    numbers: {numbers}
  </>
)


// onChange "q" - no rerender
// onChange "qw" - no rerender
// onChange "qw1" - rerender
// onChange "qw1e" - no rerender

Use update

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useUpdate is a similar to useEffect hook, but it allows you to subscribe to atoms and receive it values in the callback. Important semantic difference is that subscription to atoms works as onChange hook and your callback will call during transaction, so you need to schedule an effects, but could mutate an atoms without batching. Subscriptions to a values works like regular useEffect hook.

The most common use case for this hook is to synchronize some state from a props or context to an atom.

import { action, atom } from '@reatom/core'
import { useAction, useUpdate } from '@reatom/npm-react'
import Form from 'form-library'


const formValuesAtom = atom({})
const submit = action((ctx) => api.submit(ctx.get(formValuesAtom)))


const Sync = () => {
  const { values } = useFormState()
  useUpdate((ctx, values) => formValuesAtom(ctx, values), [values])
  return null
}
// or just
const Sync = () => useUpdate(formValuesAtom, [useFormState().values])


export const MyForm = () => {
  const handleSubmit = useAction(submit)


  return (
    <Form onSubmit={handleSubmit}>
      <Sync />
      .....
    </Form>
  )
}

And it works well in the opposite direction, you could synchronise an atom’s data with the local state, or do any other kind of effect. You can use useUpdate as a safety replacement for onChange + useEffect.

For example, you need a controlled input from the passed atom.

Here is a naive implementation:

export const Item = ({ itemAtom }) => {
  const [value, setValue] = React.useState('')


  React.useEffect(() => {
    const cleanup = itemAtom.onChange((ctx, state) => setValue(state))
    // DO NOT FORGET TO RETURN THE CLEANUP
    return cleanup
  }, [itemAtom])


  return (
    <input value={value} onChange={(e) => setValue(e.currentTarget.value)} />
  )
}

Here is a simpler and more reliable implementation:

export const Item = ({ itemAtom }) => {
  const [value, setValue] = React.useState(itemAtom)


  useUpdate((ctx, state) => setValue(state), [itemAtom])


  return (
    <input value={value} onChange={(e) => setValue(e.currentTarget.value)} />
  )
}

Use atom promise

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If you have an atom with a promise and want to use its value directly, you could use useAtomPromise. This function relies on React Suspense↗ and throws the promise until it resolves. It can be useful with reatomResource.

import { atom, reatomResource } from '@reatom/framework'
import { useAtom, useAction, useAtomPromise } from '@reatom/npm-react'


const pageAtom = atom(1, 'pageAtom')
const listReaction = reatomResource(async (ctx) => {
  const page = ctx.spy(pageAtom)
  const response = await ctx.schedule(() => fetch(`/api/list?page=${page}`))
  if (!response.ok) throw new Error(response.statusText)
  return response.json()
})


export const List = () => {
  const [page] = useAtom(pageAtom)
  const prev = useAction((ctx) =>
    pageAtom(ctx, (state) => Math.max(1, state - 1)),
  )
  const next = useAction((ctx) => pageAtom(ctx, (state) => state + 1))
  const list = useAtomPromise(listReaction.promiseAtom)


  return (
    <section>
      <ul>
        {list.map((el) => (
          <li key={el.id}>...</li>
        ))}
      </ul>
      <hr />
      <button onClick={prev}>prev</button>
      {page}
      <button onClick={next}>next</button>
    </section>
  )
}

Use context creator

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Sometimes, you can only create ctx inside a React component, for example, in SSR. For that case, we have the useCreateCtx hook.

export const App = () => {
  const ctx = useCreateCtx((ctx) => {
    // do not use logger in a server (SSR)
    if (typeof window !== 'undefined') {
      connectLogger(ctx)
    }
  })


  return (
    <reatomContext.Provider value={ctx}>
      <Component {...pageProps} />
    </reatomContext.Provider>
  )
}

Examples

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Setup batching for old React

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For React 16 and 17 you need to setup batching by yourself in the root of your app.

For react-dom:

import { unstable_batchedUpdates } from 'react-dom'
import { createCtx } from '@reatom/core'
import { setupBatch, withBatching } from '@reatom/npm-react'


setupBatch(unstable_batchedUpdates)
const ctx = withBatching(createCtx())

For react-native:

import { unstable_batchedUpdates } from 'react-native'
import { createCtx } from '@reatom/core'
import { setupBatch } from '@reatom/npm-react'


setupBatch(unstable_batchedUpdates)
const ctx = withBatching(createCtx())