Adapter for react.

Installation

1npm i @reatom/npm-react

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

Read the handbook first for production usage.

Setup context

You need to set up the main context once and wrap your application in a provider at the top level.

1import { createCtx, connectLogger } from '@reatom/framework'
2import { reatomContext } from '@reatom/npm-react'
3import { Main } from './path/to/an/Main'
4
5const ctx = createCtx()
6if (import.meta.env.DEV) {
7  connectLogger(ctx)
8}
9
10export const App = () => (
11  <reatomContext.Provider value={ctx}>
12    <Main />
13  </reatomContext.Provider>
14)

Use atom

reatomComponent

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.

1import { atom } from '@reatom/core'
2import { reatomComponent } from '@reatom/npm-react'
3
4export const countAtom = atom(0)
5export const Counter = reatomComponent(
6  ({ ctx }) => <input type="number" value={ctx.spy(count)} onChange={(e) => countAtom(ctx, e.target.valueAsNumber)} />,
7  'Counter',
8)

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. Also, you can use additional bind method instead of useAction to bind an action to the component.

1import { atom, Atom } from '@reatom/core'
2import { reatomComponent } from '@reatom/npm-react'
3
4export const Counter = reatomComponent<{
5  atom: Atom<number>
6  onChange: Action
7}>(({ 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.

1export const SomeList = reatomComponent(
2  ({ ctx }) =>
3    ctx.spy(isLoadingAtom) ? (
4      <span>Loading...</span>
5    ) : (
6      <ul>
7        {ctx.spy(listAtom).map((el) => (
8          <li>{el.text}</li>
9        ))}
10      </ul>
11    ),
12  'SomeList',
13)

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

Unmount

An important feature of reatomComponent is automatic resource management with default for Reatom AbortController in the cause context. You may be familiar with this concept from @reatom/effects. The ctx in reatomComponent props includes the AbortController which is followed by all derived actions. For example, it means if you will update an atom from the component and it will cause reatomResource refetch and the component will unmaunt before the fetch end - the fetch will throw an abort error.

This increases the stability of your application as it reduces the amount of possible race conditions. But be aware that sometimes you may want to create a request that you don't want to abort even if the unmount occurs. For example, it might be an analytic event, in which case you should use spawn.

useAtom

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:

1import { action, atom } from '@reatom/core'
2import { useAction, useAtom } from '@reatom/npm-react'
3
4// base mutable atom
5const inputAtom = atom('', 'inputAtom')
6// computed readonly atom
7const greetingAtom = atom((ctx) => `Hello, ${ctx.spy(inputAtom)}!`, 'greetingAtom')
8// action to do things
9const onChange = action(
10  (ctx, event: React.ChangeEvent<HTMLInputElement>) => inputAtom(ctx, event.currentTarget.value),
11  'onChange',
12)
13
14export const Greeting = () => {
15  const [input] = useAtom(inputAtom)
16  const [greeting] = useAtom(greetingAtom)
17  const handleChange = useAction(onChange)
18
19  return (
20    <>
21      <input value={input} onChange={handleChange} />
22      {greeting}
23    </>
24  )
25}

We recommend to setup logger here.

Use atom selector

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).

1import { useAtom } from '@reatom/npm-react'
2import { goodsAtom } from '~/goods/model'
3
4export const GoodsItem = ({ idx }: { idx: number }) => {
5  const [element] = useAtom((ctx) => ctx.spy(goodsAtom)[idx], [idx])
6
7  return <some-jsx {...element} />
8}

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.

1import { useAtom } from '@reatom/npm-react'
2import { activeAtom, goodsAtom } from '~/goods/model'
3
4export const GoodsItem = ({ idx }: { idx: number }) => {
5  const [element] = useAtom((ctx) => (ctx.spy(activeAtom) === idx ? ctx.spy(listAtom)[idx] : null), [idx])
6
7  if (!element) return null
8
9  return <some-jsx {...element} />
10}

Advanced usage

Check this out!

1export const Greeting = ({ initialGreeting = '' }) => {
2  const [input, setInput, inputAtom] = useAtom(initialGreeting)
3  const [greeting] = useAtom((ctx) => `Hello, ${ctx.spy(inputAtom)}!`, [inputAtom])
4  // you could do this
5  const handleChange = useCallback((event) => setInput(event.currentTarget.value), [setInput])
6  // OR this
7  const handleChange = useAction((ctx, event) => inputAtom(ctx, event.currentTarget.value), [inputAtom])
8
9  return (
10    <>
11      <input value={input} onChange={handleChange} />
12      {greeting}
13    </>
14  )
15}

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

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.

1const [input, setInput] = useState('')
2const 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.

1const [input, setInput, inputAtom, ctx] = useAtom('')
2const handleSubmit = useCallback(() => props.onSubmit(ctx.get(inputAtom)), [props.onSubmit, inputAtom, ctx])

Btw, you could use useAction.

1const [input, setInput, inputAtom] = useAtom('')
2const handleSubmit = useAction((ctx) => props.onChange(ctx.get(inputAtom)), [props.onChange, inputAtom])

Prevent rerenders

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.

1const [filter, setFilter, filterAtom] = useAtom('', [], false)
2const [data, setData, dataAtom] = useAtom([], [], false)
3const handleSubmit = useAction(
4  (ctx) =>
5    ctx.schedule(() =>
6      fetch(`api/search?q=${ctx.get(filterAtom)}`)
7        .then((res) => res.json())
8        .then(setData),
9    ),
10  [filterAtom, dataAtom],
11)
12
13return (
14  <>
15    <Filter atom={filterAtom} />
16    <Table atom={dataAtom} />
17    {/* this will not rerender by filters or data changes */}
18    <OtherComponent />
19  </>
20)

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

1// this component will not rerender by `inputAtom` change, only by `numbers` change
2const [, , inputAtom] = useAtom('', [], false)
3const handleChange = useAction((ctx, event) => inputAtom(ctx, event.currentTarget.value), [inputAtom])
4const [numbers] = useAtom((ctx) => ctx.spy(inputAtom).replace(/\D/g, ''), [inputAtom])
5
6return (
7  <>
8    <input onChange={handleChange} />
9    numbers: {numbers}
10  </>
11)
12
13// onChange "q" - no rerender
14// onChange "qw" - no rerender
15// onChange "qw1" - rerender
16// onChange "qw1e" - no rerender

Use action

To bind your actions to relative context you need to use useAction, it will just remove the first ctx parameter from your action and return a function which accepts all other needed parameters.

1const pageAtom = atom(0, 'pageAtom')
2const next = action((ctx) => pageAtom(ctx, (page) => page + 1), 'pageAtom.next')
3const prev = action((ctx) => pageAtom(ctx, (page) => Math.max(1, page - 1)), 'pageAtom.prev')
4
5export const Paging = () => {
6  const [page] = useAtom(pageAtom)
7  const handleNext = useAction(next)
8  const handlePrev = useAction(prev)
9
10  return (
11    <>
12      <button onClick={handlePrev}>prev</button>
13      {page}
14      <button onClick={handleNext}>next</button>
15    </>
16  )
17}

useAction accepts any function with ctx parameter, not only action, so you can write inline function, use props, and it will still memoized and return the same stable function reference, just like useEvent

1export const Paging = ({ pageAtom }: { pageAtom: Atom<number> }) => {
2  const [page] = useAtom(pageAtom)
3  const handleNext = useAction((ctx) => pageAtom(ctx, (page) => page + 1))
4  const handlePrev = useAction((ctx) => pageAtom(ctx, (page) => Math.max(1, page - 1)))
5
6  return (
7    <>
8      <button onClick={handlePrev}>prev</button>
9      {page}
10      <button onClick={handleNext}>next</button>
11    </>
12  )
13}

Also, you can use useAction to get an atom setter without subscribing to it.

1export const PagingAction = ({ pageAtom }: { pageAtom: Atom<number> }) => {
2  const setPage = useAction(pageAtom)
3
4  return (
5    <>
6      <button onClick={() => setPage((page) => Math.max(1, page - 1))}>prev</button>
7      <button onClick={() => setPage((page) => page + 1)}>next</button>
8    </>
9  )
10}

Use update

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.

1import { action, atom } from '@reatom/core'
2import { useAction, useUpdate } from '@reatom/npm-react'
3import Form from 'form-library'
4
5const formValuesAtom = atom({})
6const submit = action((ctx) => api.submit(ctx.get(formValuesAtom)))
7
8const Sync = () => {
9  const { values } = useFormState()
10  useUpdate((ctx, values) => formValuesAtom(ctx, values), [values])
11  return null
12}
13// or just
14const Sync = () => useUpdate(formValuesAtom, [useFormState().values])
15
16export const MyForm = () => {
17  const handleSubmit = useAction(submit)
18
19  return (
20    <Form onSubmit={handleSubmit}>
21      <Sync />
22      .....
23    </Form>
24  )
25}

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:

1export const Item = ({ itemAtom }) => {
2  const [value, setValue] = React.useState('')
3
4  React.useEffect(() => {
5    const cleanup = itemAtom.onChange((ctx, state) => setValue(state))
6    // DO NOT FORGET TO RETURN THE CLEANUP
7    return cleanup
8  }, [itemAtom])
9
10  return <input value={value} onChange={(e) => setValue(e.currentTarget.value)} />
11}

Here is a simpler and more reliable implementation:

1export const Item = ({ itemAtom }) => {
2  const [value, setValue] = React.useState(itemAtom)
3
4  useUpdate((ctx, state) => setValue(state), [itemAtom])
5
6  return <input value={value} onChange={(e) => setValue(e.currentTarget.value)} />
7}

Use atom promise

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.

1import { atom, reatomResource } from '@reatom/framework'
2import { useAtom, useAction, useAtomPromise } from '@reatom/npm-react'
3
4const pageAtom = atom(1, 'pageAtom')
5const listReaction = reatomResource(async (ctx) => {
6  const page = ctx.spy(pageAtom)
7  const response = await ctx.schedule(() => fetch(`/api/list?page=${page}`))
8  if (!response.ok) throw new Error(response.statusText)
9  return response.json()
10})
11
12export const List = () => {
13  const [page] = useAtom(pageAtom)
14  const prev = useAction((ctx) => pageAtom(ctx, (state) => Math.max(1, state - 1)))
15  const next = useAction((ctx) => pageAtom(ctx, (state) => state + 1))
16  const list = useAtomPromise(listReaction.promiseAtom)
17
18  return (
19    <section>
20      <ul>
21        {list.map((el) => (
22          <li key={el.id}>...</li>
23        ))}
24      </ul>
25      <hr />
26      <button onClick={prev}>prev</button>
27      {page}
28      <button onClick={next}>next</button>
29    </section>
30  )
31}

Use context creator

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

1export const App = () => {
2  const ctx = useCreateCtx((ctx) => {
3    // do not use logger in a server (SSR)
4    if (typeof window !== 'undefined') {
5      connectLogger(ctx)
6    }
7  })
8
9  return (
10    <reatomContext.Provider value={ctx}>
11      <Component {...pageProps} />
12    </reatomContext.Provider>
13  )
14}

Examples

• Migration from RTK to Reatom (2 times less code, -8kB gzip)

Setup batching for old React

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

For react-dom:

1import { unstable_batchedUpdates } from 'react-dom'
2import { createCtx } from '@reatom/core'
3import { setupBatch, withBatching } from '@reatom/npm-react'
4
5setupBatch(unstable_batchedUpdates)
6const ctx = withBatching(createCtx())

For react-native:

1import { unstable_batchedUpdates } from 'react-native'
2import { createCtx } from '@reatom/core'
3import { setupBatch } from '@reatom/npm-react'
4
5setupBatch(unstable_batchedUpdates)
6const ctx = withBatching(createCtx())