react-spring/packages/shared/src/hooks/useIsMounted.ts

import { useRef } from 'react'
import { useIsomorphicLayoutEffect } from './useIsomorphicLayoutEffect'

export const useIsMounted = () => {
  const isMounted = useRef(false)
  useIsomorphicLayoutEffect(() => {
    isMounted.current = true

    return () => {
      isMounted.current = false
    }
  }, [])

  return isMounted
}