Using getter to calculate computed values

Hey!

Is it ok to use the getter to return a computed value in a function? Since using it in a value doesn’t work?

Example:

const [useAuth] = create((set, get) => ({
    user: {username: undefined, authLevel: 0},
    // isSignedIn: !!get().user.username // doesn't work because it's executed before the store is created, so get() returns undefined right?
    isSignedIn: () => !!get().user.username // should work, just call isSignedIn() instead of using as a value, in the components?
})}

Also, I feel like computed values are a cool features for state management libraries to have out of the box, are there planes to add it? Do you guys need help with it somehow?

[woehrl01]

I’d like to share that it’s definitely possible to have computed fields, it just needs to be constructed differently to don’t fall into the Object.assign issue. But this requirement makes the code even more readable and explicit:

const [useAuth] = create((set, get) => ({
    user: {username: undefined, authLevel: 0},
    computed: { //yes, just use a nested object, which can be easily used in `Object.assign`
       get isSignedIn: () => !!get().user.usernamecomponents?
    }
})}

//usage
const isSignedIn = useState(s => s.computed.isSignedIn)

[dai-shi]

Summary: So there are two topics in this issue. a) Support object getters in store b) Chaining computed values (aka atoms)

For b), we are planning a new project coming soon, and it’s outside the scope of zustand.

For a), it’s a possible enhancement, but the implementation might be a bit tricky. I’m not sold much, because we don’t support b) anyway.

We should be able to do this without object getters.

const useAuth = create((set, get) => ({
    user: {username: undefined, authLevel: 0},
    signedIn: () => !!get().user.username
})}

// in components
function Foo() {
  const signedIn = useAuth(state => state.signedIn())

// vanilla non-reactive
const signedIn = useAuth.getState().singedIn()
// vanilla reactive
useAuth.subscribe(signedIn => console.log(signedIn), state => state.signedIn())

---

Now, reading the thread from the beginning again, I noticed I misunderstood the original issue. The OP never said object getters. So, the above example would be the answer.

That said, I think it’s fairly OK to mark this issue as resolved.