[Bug]: hook-use-state reports when setter is not destructured

[AndrewBoklashko]

Is there an existing issue for this?

• I have searched the existing issues and my issue is unique
• My issue appears in the command-line and not only in the text editor

Description Overview

Sometimes it's necessary to initialize value but never update it. To get a ref-like behavior with more convinient API.

The following code:

const [eventBus] = useState(() => new EventEmitter());

Produces a warning when react/hook-use-state rule is enabled:

Expected Behavior

I acknowledge that this is kind of controvercial because currently it also protects from forgetting a setter. Thus I suggest this behavior to be configurable. Furthermore, config can be done in 2 ways:

1. opt-in: add allowMissingSetter - boolean(default false)
2. opt-out: setterIgnorePattern - RegExp that will allow to opt-out of setter check. This is similar to ESLint's no-unused-vars varsIgnorePattern config.

I prefer solution 2 as it's not only more flexible and consistent but also protects from missing setter. The code above could be rewritten as:

const [eventBus, _] = useState(() => new EventEmitter());

This way it explicitly means: I don't need a setter.

eslint-plugin-react version

7.37.3

eslint version

8.57.0

node version

20

[ljharb]

It seems pretty strange to me to have state that you never change. Is there a reason you're not using useMemo for this?

[AndrewBoklashko]

Yes, from React docs:

However, since useMemo is performance optimization, not a semantic guarantee, React may throw away the cached value if there is a specific reason to do that.

In my example that state variable is used to hold a complex state object - EventEmitter(in other cases it could be e.g. a props-bounded store instance). It is important for EventEmitter instance to never re-initialize since it may lead to lost events, broken subscriptions etc. for a components that uses it.

Also inspired by blog post: useState for one-time initializations

[ljharb]

Makes sense. In that case, I think the two choices here are:

1. you can use an eslint override comment, since this use case is presumably rare
2. we can add an option to the rule (your option 1 above)