useAtomEffect

useAtomEffect runs side effects in response to changes in atoms or props using atomEffect.

The effectFn reruns whenever the atoms it depends on change or the effectFn itself changes. Be sure to memoize the effectFn if it's a function defined in the component.

⚠️ Note: always prefer to use a stable version of useMemo and useCallback to avoid extra atomEffect recomputations. You may rely on useMemo as a performance optimization, but not as a semantic guarantee. In the future, React may choose to “forget” some previously memoized values and recalculate them on next render, e.g. to free memory for offscreen components.

import { useMemoOne as useStableMemo } from 'use-memo-one'
import { useAtomValue } from 'jotai/react'
import { atomEffect } from 'jotai-effect'

type EffectFn = Parameters<typeof atomEffect>[0]

export function useAtomEffect(effectFn: EffectFn) {
  useAtomValue(useStableMemo(() => atomEffect(effectFn), [effectFn]))
}

Example Usage

import { useCallbackOne as useStableCallback } from 'use-memo-one'
import { atom, useAtom } from 'jotai'
import { atomFamily } from 'jotai/utils'
import { useAtomEffect } from './useAtomEffect'

const channelSubscriptionAtomFamily = atomFamily<Channel>(
  (channelId: string) => {
    return atom(new Channel(channelId))
  },
)
const messagesAtom = atom<Message[]>([])

function Messages({ channelId }: { channelId: string }) {
  const [messages] = useAtom(messagesAtom)
  useAtomEffect(
    useStableCallback(
      (get, set) => {
        const channel = get(channelSubscriptionAtomFamily(channelId))
        const unsubscribe = channel.subscribe((message) => {
          set(messagesAtom, (prev) => [...prev, message])
        })
        return unsubscribe
      },
      [channelId],
    ),
  )
  return (
    <>
      <h1>You have {messages.length} messages</h1>
      <hr />
      {messages.map((message) => (
        <div key={message.id}>{message.text}</div>
      ))}
    </>
  )
}