Guide on generating a typescript type for enabling read-only tuples from a constant value

Here's the interface I'm working with:

interface Test {
    data: string[]
}

const DATA_LIST = {
    USER: ["some string"],
    OTHER: ["some other string", "random value", "etc"]
} as const;

const test : Test = {
    data: DATA_LIST.OTHER
}

The issue arises when I try to assign DATA_LIST.OTHER to data, as my use case requires assigning multiple tuples to data.

This assignment doesn't work because data only accepts string[], while I am attempting to assign a readonly tuple.

Is there a more efficient way to achieve this?

Link to TypeScript Playground for further exploration.

Answer №1

The main issue at hand is as follows:

When 'readonly ["another string", "random value", "etc"]' is of type 'readonly', it cannot be assigned to the mutable type 'string[]'.

This essentially means that you are unable to assign a string[] to a readonly string[].

If you wish to reassign test.data later on, you can simply use data: [...DATA_LIST.OTHER], removing the readonly restriction and allowing assignment to a basic string[] property.

However, if you prefer to prevent reassignment of test.data, you have the option to change the property type to either readonly string[] or string[] | readonly string[].

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