slate/packages/slate-react/src/hooks/use-is-mounted.tsx

import { useEffect, useRef } from 'react'

export function useIsMounted() {
  const isMountedRef = useRef(false)

  useEffect(() => {
    isMountedRef.current = true
    return () => {
      isMountedRef.current = false
    }
  }, [])

  return isMountedRef.current
}