Reatom adapter for react.

Note, that you don't require this adapter for simple usages, native useSyncExternalStore will be enough!

import { useSyncExternalStore } from 'react'
import { atom } from '@reatom/core'

export const page = atom(0, 'page').extend((target) => ({
  next: () => target.set((state) => state + 1),
  prev: () => target.set((state) => Math.max(0, state - 1)),
}))

export const Paging = () => {
  const state = useSyncExternalStore(page.subscribe, page)

  return (
    <span>
      <button onClick={page.prev}>prev</button>
      {state}
      <button onClick={page.next}>next</button>
    </span>
  )
}

Using Hooks (Alternative API)

While reatomComponent (see below) is the preferred way to use Reatom in React, you can also use traditional React hooks if you prefer that pattern:

import { atom, withActions } from '@reatom/core'
import { useAtom, useAction } from '@reatom/react'

const pageAtom = atom(1, 'page').extend(
  withActions((target) => ({
    next: () => target.set((state) => state + 1),
    prev: () => target.set((state) => Math.max(1, state - 1)),
  })),
)

export const Pagination = () => {
  const [page] = useAtom(pageAtom)
  const handleNext = useAction(pageAtom.next)
  const handlePrev = useAction(pageAtom.prev)

  return (
    <div>
      <button onClick={handlePrev}>Prev</button>
      <span>{page}</span>
      <button onClick={handleNext}>Next</button>
    </div>
  )
}

See the Hooks API section below for more details.

Installation

npm i @reatom/react

Read the handbook first for production usage.

Binding Atoms to Components

Reatom offers powerful ways to integrate state management directly into your React components, ensuring reactivity and proper lifecycle management.

reatomComponent

The primary API to bind atoms and actions to a component's lifetime is reatomComponent. It wraps your regular React component function, placing it within a Reatom reactive context.

Features:

• Reactive Reads: Simply call an atom (myAtom()) within the component function to read its value and subscribe to updates. The component will automatically re-render when the atom changes.
• Standard React: Use any other React hooks (useState, useEffect, etc.), accept props, and return any valid ReactNode as usual.
• Context Preservation: Event handlers should be wrapped with wrap() (e.g., onClick={wrap(myAction)}) to preserve the reactive context, especially for async operations or actions updating state.
• No Hooks Rules for Atoms: Call and subscribe to atoms conditionally within your render logic without violating React's rules of hooks.
• Automatic Cleanup: Integrates with Reatom's abort context. Effects or async operations triggered from within the component (using wrap or implicitly by actions) are automatically aborted if the component unmounts before completion, preventing race conditions and memory leaks.

import { atom, wrap } from '@reatom/core'
import { reatomComponent } from '@reatom/react'

export const page = atom(0, 'page').extend((target) => ({
  next: () => target((state) => state + 1),
  prev: () => target((state) => Math.max(0, state - 1)),
}))

// Simple component reading and updating global state
export const Paging = reatomComponent(
  () => (
    <span>
      <button onClick={wrap(page.prev)}>prev</button> {/* Use wrap */}
      {page()} {/* Read atom value */}
      <button onClick={wrap(page.next)}>next</button> {/* Use wrap */}
    </span>
  ),
  'Paging',
) // Naming the component is crucial for debugging!

// Component accepting props (including atoms)
type CounterProps = {
  label: string
  count: Atom<number>
  increment: Action<[], number>
}

export const Counter = reatomComponent<CounterProps>(
  ({ label, count, increment }) => (
    <div>
      {label}: {count()}
      <button onClick={wrap(increment)}> + </button>
    </div>
  ),
  'Counter',
)

// Conditional rendering based on atom values
export const SomeList = reatomComponent(
  () =>
    isLoading() ? ( // Read atom conditionally
      <span>Loading...</span>
    ) : (
      <ul>
        {list().map(
          (
            el, // Read another atom
          ) => (
            <li key={el.id}>{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!

Unmount Behavior

A key feature of reatomComponent is its integration with Reatom's abort mechanism. When a reatomComponent unmounts:

1. Its associated reactive context is aborted.
2. Any pending async operations initiated within that context (e.g., await wrap(fetch(...)), await wrap(sleep(...))) are automatically cancelled.
3. Any active effect primitives created within its context are automatically cleaned up.

This robust cleanup prevents common issues like trying to update state on unmounted components and avoids memory leaks from lingering subscriptions or timers. If you need an operation to survive component unmount (e.g., analytics), use spawn from the core package.

reatomFactoryComponent (Recommended for Local State/Effects)

While reatomComponent is great for reading atoms state, reatomFactoryComponent is the recommended pattern for components that need their own local, encapsulated state and side effects.

It separates the component logic into two parts:

1. Factory Function: Runs once when the component instance is created. This is where you define local atoms, actions, and effects specific to this component instance. It receives the component's initial props.
2. Render Function: Runs on every render, just like a regular React component function. It has access to the atoms and actions created in the factory scope and the current props.

Benefits:

• True Encapsulation: Local state and effects are tied to the component instance, not shared globally.
• Lifecycle Management: The factory scope provides a natural place for setup logic.
• Perfect for effect: effect primitives created in the factory are automatically cleaned up when the component unmounts, making it ideal for managing local subscriptions, timers, animations, etc.
• Stable References: Atoms, actions or any other functions created in the factory have stable references across renders.

import { atom, action, effect, wrap, sleep } from '@reatom/core'
import { reatomFactoryComponent } from '@reatom/react'

// Example: A self-contained counter component
const Counter = reatomFactoryComponent<{ initialCount: number; step?: number }>(
  // 1. Factory Function (runs once per instance)
  (initProps) => {
    // Note that the props will not change in this initialization scope.
    const step = initProps.step ?? 1
    // Create local atom specific to this Counter instance
    const count = atom(initProps.initialCount, 'localCount')
    // Create local action
    const increment = action(() => count((c) => c + step), 'increment')
    const decrement = action(() => count((c) => c - step), 'decrement')

    // Example: Log changes (effect cleans up automatically)
    effect(() => {
      const currentCount = count()
      console.log(`Counter ${initProps.initialCount} changed to:`, currentCount)
      // Cleanup function (optional, runs before next effect run or on unmount)
      return () =>
        console.log(
          `Counter ${initProps.initialCount} leaving state:`,
          currentCount,
        )
    }, 'logEffect')

    // Return the render function
    return (props) => (
      <div>
        Count (Initial: {props.initialCount}, Step: {props.step ?? 1}):{' '}
        {count()}
        <button onClick={wrap(decrement)}>-</button>
        <button onClick={wrap(increment)}>+</button>
      </div>
    )
  },
  'Counter', // Name the factory component!
)

// Usage:
// <Counter initialCount={10} />
// <Counter initialCount={0} step={5} />

Example: Using effect for Auto-Cleaning

reatomFactoryComponent combined with effect is excellent for managing resources that need cleanup. It is more powerful and precise primitive than useEffect, as it isn't coupled with rerenders.

import { atom, effect, wrap, sleep, isAbort } from '@reatom/core'
import { reatomFactoryComponent } from '@reatom/react'

const IntervalLogger = reatomFactoryComponent<{ intervalMs: number }>(
  ({ intervalMs }) => {
    const tick = atom(0, 'tick')

    // This effect runs a timer and cleans it up automatically on unmount
    effect(async () => {
      while (true) {
        // sleep respects the abort context
        await wrap(sleep(intervalMs))
        tick((t) => t + 1)
      }
    }, 'intervalEffect')

    return (props) => (
      <div>
        Interval ({props.intervalMs}ms) Ticks: {tick()}
      </div>
    )
  },
  'IntervalLogger',
)

// Usage:
// <IntervalLogger intervalMs={1000} />
// When this component unmounts, the interval stops automatically.

reatomFactoryComponent provides a robust and elegant way to build stateful, effectful components with automatic lifecycle management, leveraging the power of Reatom's core primitives like atom and effect.

Hooks API

While reatomComponent is the preferred way to use Reatom in React (see above), you can also use traditional React hooks if you prefer that pattern. The hooks API provides a familiar useState-like experience while maintaining Reatom's reactivity.

useAtom

useAtom is the main hook for reading atoms and creating local state. It accepts an atom to read its value and subscribe to changes, or a primitive value to create a new mutable atom. It's similar to useState, but with additional features. It returns a tuple of [state, setState, theAtom, frame]. theAtom is a reference to the passed or created atom.

Reading an existing atom:

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

const inputAtom = atom('', 'inputAtom')
const greetingAtom = computed(() => `Hello, ${inputAtom()}!`, 'greetingAtom')

const onChange = action(
  (event: React.ChangeEvent<HTMLInputElement>) =>
    inputAtom.set(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}
    </>
  )
}

Creating local atom from primitive:

export const Counter = () => {
  const [count, setCount] = useAtom(0)

  return (
    <div>
      <span>{count}</span>
      <button onClick={() => setCount((c) => c + 1)}>+</button>
      <button onClick={() => setCount((c) => c - 1)}>-</button>
    </div>
  )
}

Creating local computed atom:

You can create a computed atom inline by passing a function and a dependencies array:

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

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

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

The computed function is called within the reactive context, so you can directly call atoms to track dependencies. It will be called only when the dependencies change, so you can use conditions and Reatom will optimize your dependencies and subscribe only to the necessary atoms.

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

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

  if (!element) return null

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

Advanced usage with local atoms:

export const Greeting = ({ initialGreeting = '' }) => {
  const [input, setInput, inputAtom] = useAtom(initialGreeting)
  const [greeting] = useAtom(() => `Hello, ${inputAtom()}!`, [inputAtom])

  const handleChange = useAction(
    (event) => inputAtom.set(event.currentTarget.value),
    [inputAtom],
  )

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

Preventing re-renders with subscribe: false:

useAtom accepts a third argument options where you can set subscribe: false to read an atom value without subscribing to changes. This is useful when you need to share data created and managed in a parent, but used in children.

const [filter, setFilter, filterAtom] = useAtom('', [], { subscribe: false })
const [data, setData, dataAtom] = useAtom([], [], { subscribe: false })
const handleSubmit = useAction(
  () =>
    fetch(`api/search?q=${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 />
  </>
)

useAction

useAction binds your actions to the Reatom context and provides stable function references with fresh closure capture — the same behavior as the React useEvent RFC.

Why this matters:

1. Stable reference: The returned function identity never changes across re-renders, so you can safely pass it to memoized children without causing unnecessary re-renders.
2. Fresh closures: Unlike useCallback, the function always "sees" the latest props and state values — no stale closure bugs, no dependency arrays to manage.
3. Frame binding: The callback is automatically bound to the component's Reatom frame, so async operations respect the component lifecycle (abort on unmount). You don't need to use wrap inside the callback — it's already wrapped.

Binding an existing action:

const pageAtom = atom(0, 'pageAtom')
const next = action(() => pageAtom.set((page) => page + 1), 'pageAtom.next')
const prev = action(
  () => pageAtom.set((page) => Math.max(1, page - 1)),
  'pageAtom.prev',
)

export const Paging = () => {
  const [page] = useAtom(pageAtom)
  const handleNext = useAction(next)
  const handlePrev = useAction(prev)

  return (
    <>
      <button onClick={handlePrev}>prev</button>
      {page}
      <button onClick={handleNext}>next</button>
    </>
  )
}

Using inline functions (useEvent pattern):

When you pass an inline function, useAction wraps it in an action and ensures the callback always uses the latest closure values while maintaining a stable reference:

export const Paging = ({ pageAtom }: { pageAtom: Atom<number> }) => {
  const [page] = useAtom(pageAtom)
  const handleNext = useAction(() => pageAtom.set((page) => page + 1))
  const handlePrev = useAction(() =>
    pageAtom.set((page) => Math.max(1, page - 1)),
  )

  return (
    <>
      <button onClick={handlePrev}>prev</button>
      {page}
      <button onClick={handleNext}>next</button>
    </>
  )
}

This is especially useful for event handlers that reference props or local state — you get the ergonomics of inline functions without the downsides of useCallback.

Setup context

Optionally, you need to set up the main context once and wrap your application in a provider at the top level. This is required if you have called clearStack() (recommended).

import { context, connectLogger, clearStack } from '@reatom/core'
import { reatomContext } from '@reatom/react'
import { Main } from './path/to/an/Main'

// Recommended: Disable default context for predictability
clearStack()

const rootFrame = context.start()
if (import.meta.env.DEV) {
  rootFrame.run(connectLogger)
}

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