Create an object type that uses an object's values as the key in the typescript

Question

I am creating a function called formatAddress which accepts an address object and property map object as input and outputs the mapped address.

function formatAddress(address, map): MappedAddressOutput {
   ...
}

type MappedAddressOutput = AnyObject[typeof AddressMap[keyof typeof AddressMap]];

interface Address {
    addressLine1: string;
    addressLine2: string;
    city: string;
    province: string;
    postalCode: string;
}

const AddressMap = {
    addressLine1: "address1",
    addressLine2: "address2",
    city: "city",
    province: "province",
    postalCode: "postalCode"
};
type IndexSignature = string | number | symbol; 
type AnyObject = { [key: IndexSignature]: any };

If I wish to transform the MappedAddressOutput as the code below:

type MappedAddressOutput = ObjectValueAsKey<AddressMap>

How can I implement ObjectValueAsKey type?

Answer 1

Use a generic type parameter so you can use the given map in the return type:

function formatAddress<To extends Record<keyof Address, string>>(address: Address, map: To): {
    [K in keyof Address as To[K]]: Address[K];
} {
    return Object.entries(address).map(([k, v]) => [map[k as keyof typeof map], v]);
}

Then when you use it, you have to make sure the map is inferred literally. The simplest way to do that is to use as const:

interface Address {
    addressLine1: string;
    addressLine2: string;
    city: string;
    province: string;
    postalCode: string;
}

const exampleMap = {
    addressLine1: "address1",
    addressLine2: "address2",
    city: "city",
    province: "province",
    postalCode: "postalCode"
} as const;

const result = formatAddress({
    addressLine1: "",
    addressLine2: "",
    city: "",
    province: "",
    postalCode: "",
}, exampleMap);

and now the type of result is

{
    address1: string;
    address2: string;
    city: string;
    province: string;
    postalCode: string;
}

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