useSelector question

[AleksandrukTad]

Hey,
I have found this post: #36 I got question about it. Am I understanding this right that useSelector will slice the bigAtom, get a read only value from it and will not rerender the component when some other value in bigAtom is updated?

example:
const errorsAtoms = atom({ firstName: "", secondName: "", lastName: "" })

const firstNameError = useSelector(errorsAtoms , (errors) => errors.firstName);
const secondNameError = useSelector(errorsAtoms , (errors) => errors.secondName);
const lastNameError = useSelector(errorsAtoms , (errors) => errors.lastName);

When I have tree like that

Form

• FirstName
• SecondName
• LastName

When the the secondName fails validation during submit and now errorsAtoms is like so:
const errorsAtoms = atom({ firstName: "", secondName: "Failed validation", lastName: "" })

Will it rerender FirstName component?

[dai-shi]

Will it rerender FirstName component?

No. I think it work as you expect.

useSelector is a bit old, current recommendation would be simply deriving atoms:

const errorsAtom = atom({ firstName: "", secondName: "", lastName: "" })

const firstNameErrorAtom = atom((get) => get(errorsAtom).firstName);
const secondNameErrorAtom = atom((get) => get(errorsAtom).secondName);
const lastNameErrorAtom = atom((get) => get(errorsAtom).lastName);

[tjx666]

Why deriving atoms is the recommend way? I think useSelector is convenient enough and good for performance.

[dai-shi]

Because we don't need to care about making selectors stable.

I don't think there's a difference on performance. It's fine to have useSelector on userland. There are several ways to implement it depending on requirements.