React hook for getting a unique identifier for a component

useComponentId.js

import { useRef } from 'react';

let uniqueId = 0;
const getUniqueId = () => uniqueId++;

export function useComponentId() {
  const idRef = useRef(getUniqueId());
  return idRef.current;
}

You add test-related code in a component? And also you change behavior depending on how id is used the outcome might be different in test than prod.

Doesn't change behavior, just changes the id. Otherwise every run of your test, you get snapshot updates (new id on mount), which defeats the purpose of snapshots.

Why is it not needed and how do the two things relate (I don't know your shortid implementation).

I'm not sure I understand the question. I'm just saying that this:

  const idRef = useRef(null);
  if (idRef.current === null) {
    idRef.current = getUniqueId()
  }
  return idRef.current;

and this

  const idRef = useRef(getUniqueId());
  return idRef.current;

both return a unique ID that doesn't change on re-render. Which makes sense, refs wouldn't be useful if the initial value changed. Log from the calling component to see what I mean.

(shortid is just an id-generating package my org uses)

updated, typo in the second code example

You add test-related code in a component? And also you change behavior depending on how id is used the outcome might be different in test than prod.

Doesn't change behavior, just changes the id. Otherwise every run of your test, you get snapshot updates (new id on mount), which defeats the purpose of snapshots.

It does. You use different ID generation methods. If one of the different methods generate non-unique ID, it will work in one, but fail in the other or lead to different results, depending on how you use the generated ID.

Sorry. I don't get what you are talking about. You've just changed things replying to my initial question. Why is it null instead of undefined? Also you did not answer why the undefined check is not needed. I don't understand the problem.

In cases where I don't need globally unique IDs, but rather IDs unique per component I'm using this hook:

export function useIdGenerator(): () => number {
  const ref = useRef(0);

  function getId() {
    ref.current += 1;
    return ref.current;
  }

  return getId;
}

On a side note, nanoId is considerably faster than shortId or uniqueId according to their benchmarks.

There is an open issue for this on the react repo.

Here is a more robust implementation that also supports SSR.

Also, for test snapshot support, you'll want a predictable id, maybe using a different prop from the instance.

You shouldn't be using snapshots at all. write proper tests.

For anyone stumbling upon this in 2023 there's React.useId for this very purpose since React v18.