typescript interface conditional optional parameters

Question

Can we achieve this :

interface IMyInterface{
    firstname:string  // this means firstname is mandatory

    name:string  // this also means name is mandatory
}

How can I say, either one of firstname or name is optional (?), depending on if the other one is provided ?

Or if that's not possible, what are the other options ?

EDIT : This is not a duplicate of Typescript Interface - Possible to make "one or the other" properties required?.

We don't want to create a separate interface for every single optional element simply because the maintenance and naming and the refactoring will be a pain in the neck and it's not reusable.

Answer 1

Here is a generic way of saying "OneOf" these keys, you might be able to use it here:

type EachOfTmp<T> = {// to make OneOf less gross
  [K in Keys<T>]: {
    _: {[X in K]: T[K]};
  }
};

// require only one of the keys
export type OneOf<T> = EachOfTmp<T>[Keys<T>]["_"] & Partial<T>;

const thing1: OneOf<{ a: number; b: number }> = { a: 2 } // valid
const thing2: OneOf<{ a: number; b: number }> = { b: 2 } // valid
const thing3: OneOf<{ a: number; b: number }> = {} // invalid

EDIT: oops, I forgot I use this convenience Keys deal -

export type Keys<T> = keyof T;
export function Keys<T>(o: T) {
  if (!o) {
    return [];
  }
  return Object.keys(o) as Keys<T>[];
}