What is the safest method to convert a nested data structure into an immutable one while ensuring type safety when utilizing Immutable library?

Question

What is the safest method to convert a nested data structure into an immutable one while ensuring type safety when utilizing Immutable library?

When it comes to dealing with immutable data structures, Immutable provides the handy fromJs function. However, I've been facing issues trying to integrate it smoothly with Typescript. Here's what I've got:

type SubData = {
    field1: string;
}

type Data = {
    field0: string;
    subData: SubData[];
};

const arr: Data[] = [];

const list: List<Data> = fromJS(arr);
      ^^^--- compiler error

An error message is displayed stating:

Type 'List<Map<keyof Data, string | List<Map<"field1", string>>>>' is not assignable to type 'List<Data>'

I attempted to resolve this by using:

const list: List<Data> = fromJS<Data[]>(arr);

However, this approach did not provide a solution. Any suggestions on how to rectify this issue?

typescript immutable.js

Answer 1

Answer №1

To define your list in a similar manner, you can use the following syntax:

type SubDetails = Immutable.MapOf<{
    attribute1: string
}>

type DataStructure = Immutable.MapOf<{
    property0: string;
    subDetailsList: List<SubDetails>;
}>;

const dataArray: DataStructure[] = [];

const dataList: List<DataStructure> = fromJS(dataArray)

TS Playground

Note: using fromJS will create an immutable array (List) with immutable objects without deep immutability.

If you have a function that works with List<DataStructure>, it could do something like:

function processDataList(list: List<DataStructure>) {
    // modify a property
    return list.forEach(item => item.property0 = "updated value");
}

Answer 2

To define your list in a similar manner, you can use the following syntax:

type SubDetails = Immutable.MapOf<{
    attribute1: string
}>

type DataStructure = Immutable.MapOf<{
    property0: string;
    subDetailsList: List<SubDetails>;
}>;

const dataArray: DataStructure[] = [];

const dataList: List<DataStructure> = fromJS(dataArray)

TS Playground

Note: using fromJS will create an immutable array (List) with immutable objects without deep immutability.

If you have a function that works with List<DataStructure>, it could do something like:

function processDataList(list: List<DataStructure>) {
    // modify a property
    return list.forEach(item => item.property0 = "updated value");
}

What is the safest method to convert a nested data structure into an immutable one while ensuring type safety when utilizing Immutable library?

Answer №1

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