I'm programming against a web api that, for some of the fields, only returns them if you specify them in the query.
{a:"hello", b:"world", c:"of goo", d:"i am always present"}
and I called
api.getResponse(["a","b"])
I would get
{a:"hello", b:"world", d:"i am always present"}
in response.
How do i express that in the type language of typescript?
You can declare the always present and optional fields on separate interfaces then use Pick to choose the correct ones:
interface AlwaysPresentFields {
d: string;
}
interface OptionalFields {
a: string;
b: string;
c: string;
}
type ApiResponse<F extends keyof OptionalFields> = AlwaysPresentFields & Pick<OptionalFields, F>;
function getResponse<F extends keyof OptionalFields>(fields: F[]): ApiResponse<F> {
// Implementation
}
In Advanced typesscript we can use Partial, Pick, Readonly.
As in your case, keyof , Partial can be used. The same can be implemented in using Pick too: docs
interface IResponse {
a: string;
b: string;
c: string;
d: string;
}
const getResponse = (responseKeys: Array<keyof IResponse>): Partial<IResponse> => {
const responseWithFilteredKeys: Partial<IResponse> = {};
const response: IResponse = {
a: 'a',
b: 'a',
c: 'a',
d: 'a',
};
responseKeys.forEach((key: keyof IResponse) => {
responseWithFilteredKeys[key] = response[key];
});
return responseWithFilteredKeys;
};
const filterdUserResponse: Partial<IResponse> = getResponse(['a', 'b']);
