Apply constraints to type based on the key-value of another type

I have this basic type def:

export interface Person {
    name: string;
    age: number;
    created: Date;
    ...
}

The data with this type comes from a json file.
JSON.parse does not produce Date from string, so I was thinking to use the 2nd "reviver" parameter which allows you to modify the value that is being parsed based on the key.

So first I create a list of props that need to be modified:

const deserializeMap: Mapper = {
    created: v => new Date(v)
}

But I am not sure how to define the "Mapper" type.

it should be something like this:

type Mapper = {
    <K extends keyof Person >K: (value: any) => Person [K]
};

so depending on what property I define, the value returned by the function has to match the type of the property from the Person class

>Solution :

You can use a mapped type to define the mapper type:

type Mapper = {
    [K in keyof Person]: (value: any) => Person[K];
};

and then you can say that your deserializeMap satisfies a Partial<Mapper>:

const deserializeMap = {
    created: v => new Date(v)
} satisfies Partial<Mapper>;

Depending on how you use deserializeMap, you may want to use a type annotation instead:

const deserializeMap: Partial<Mapper> = {
    created: v => new Date(v)
};

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