useUpdateEffect.js

// I've only used this for focus management, I'm willing to bet you don't
// actually want to do this unless it's focus management
function useUpdateEffect(effect, deps) {
  let mounted = useRef(false)

  useEffect(() => {
    if (mounted.current) {
      return effect()
    } else {
      mounted.current = true
    }
  }, deps) // linter will hate you but whatev
}

useUpdateEffect(() => {
  console.log("your code has updated from the original value")
}, [props.code])

Could do it this way too:

function Thing({ code }) {
  let firstCode = useRef(code)
  useEffect(() => {
    if (code === firstCode.current) {
      return
    } else {
      doYourThing()
    }
  }, [code])
}

Oh, duh, that is exactly what you had in your tweet.