Argument of type 'readonly string[]' is not assignable to parameter of type 'string[]'.

[nordowl]

Describe the bug
I want to pass an urlState property of type string[] to a function. But that produces a TS error, because urlState uses readonly properties.

To Reproduce
Just some pseudo code

import { useUrlState } from "state-in-url"

function assignCats(cats: string[], owner: string) {
    return
}

type DefaultUrlState = {
    cats: string[]
    owner: string
}

const defaultState: DefaultUrlState = { cats: [], owner: "" }

const { setUrl, urlState } = useUrlState({ defaultState })

assignCats(urlState.cats, urlState.owner)

Trying to pass urlState.cats as the cats parameter throws:

Argument of type 'readonly string[]' is not assignable to parameter of type 'string[]'.
  The type 'readonly string[]' is 'readonly' and cannot be assigned to the mutable type 'string[]'

Expected behavior
No errors.

[asmyshlyaev177]

Can change assignCats to

function assignCats(cats: string[] | readonly string[], owner: string) {
    return
}

urlState.cats will be readonly so you can't accidentally mutate it.

Possible to remove readonly from returned type if it problematic, can consider it.

[asmyshlyaev177]

@nordowl does it make sense to return regular data without readonly?

[nordowl]

I think having to specify readonly everywhere you want to access the data is a step not needed. Especially if you then want to modify the data - e.g. you can't use array.push() anymore. Sure, you could use the spread operator and create a new array or what not, but that might potentially be more memory-intensive.

For now what I've done is use type casting with as, e.g. myFunc(urlState.myArray as string[]). But that's not great I think.

Having mutable array types would make things a little easier in my opinion.

[asmyshlyaev177]

@nordowl I guess it's not really needed, will remove it in a new version.

[asmyshlyaev177]

@nordowl will be released when https://github.com/asmyshlyaev177/state-in-url/actions/runs/11758298425 pass, issues closing automatically, not sure why.

[nordowl]

@asmyshlyaev177 Thanks, I appreciate it!

[asmyshlyaev177]

@asmyshlyaev177 Thanks, I appreciate it!

It's released few minutes ago.