typescript array of objects with one property in each item
I'm integrating Google Ads Rest API.I want to pass an array of type UserIdentifier to a function where each object should only have one item only because it is required by this Google Ads API for example:
f([{hashedEmail: "xxxxxx"}, {hashedPhoneNumber: "xxxxxx"}]) // OK f([{hashedEmail: "xxxxxx", hashedPhoneNumber: "xxxxxx"}]) // Not Cool This example comes close but I only want to use the keys that are mentioned in Google Ads API UserIdentifier type.
Thanks in advance.
It looks like the sort of structure you are looking for is a C-Style Union. This means that you have an object that only has one property present out of all of the listed ones. A helper generic type can easily be created to generate this structure:
type CUnion<T extends Record<string, unknown>> = { [K in keyof T]: { [_ in K]: T[K] } & { [K2 in Exclude<keyof T, K>]?: undefined } }[keyof T]; // { ssn: boolean; webauth?: undefined } | { webauth: string; ssn?: undefined } type UserID = CUnion<{ ssn: boolean; webauth: string; }>; const asdf: UserID = { ssn: true, }; const asdf2: UserID = { webauth: "hey" }; // @ts-expect-error This correctly fails. const asdf3: UserID = { ssn: true, webauth: "hey" }We need to make the other properties explicitly undefined and optional because TypeScript does not error when you specify properties in other parts of a union when they should not actually be there. Anyways, here is your code adjusted to use this solution:
type CUnion<T extends Record<string, unknown>> = { [K in keyof T]: { [_ in K]: T[K] } & { [K2 in Exclude<keyof T, K>]?: undefined } }[keyof T]; type UserIdentifier = CUnion<{ hashedEmail: string, hashedPhoneNumber: string, mobileId: string, thirdPartyUserId: string, addressInfo: { hashedFirstName: string, hashedLastName: string, city: string, state: string, countryCode: string, postalCode: string, hashedStreetAddress: string } }>; declare const f: (identifiers: UserIdentifier[]) => void; f([{ hashedEmail: "xxxxxx" }, { hashedPhoneNumber: "xxxxxx" }]) // OK -- correctly works! f([{ hashedEmail: "xxxxxx", hashedPhoneNumber: "xxxxxx" }]) // Not Cool -- correctly errors!TypeScript Playground Link