TypeScript require one parameter or the other, but not neither

Question

Say I have this type:

export interface Opts {
  paths?: string | Array,
  path?: string | Array

        

Answer 1

You are basically looking for an exclusive union type.

It has been already proposed but unfortunately, in the end, it was declined.

I found the proposed solutions here not to my liking, mostly because I'm not a fan of fancy and complex types.

Have you tried with function overloading?

I was in a similar situation and for me, this was the solution.

interface Option1 {
  paths: string | string[];
}

interface Option2 {
  path: string | string[];
}

function foo(o: Option1): void;
function foo(o: Option2): void;
function foo(o: any): any {}

foo({ path: './' });
foo({ paths: '../' });
// The folling two lines gives an error: No overload matches this call.
foo({ paths: './', path: '../' });
foo({})

With arrow function the same code as above would instead be:

interface Option1 {
  paths: string | string[];
}

interface Option2 {
  path: string | string[];
}

interface fooOverload {
  (o: Option1): void;
  (o: Option2): void;
}

const foo: fooOverload = (o: any) => {};

foo({ path: '2' });
foo({ paths: '2' });
// The following two lines gives an error: No overload matches this call.
foo({ paths: '', path: 'so' });
foo({});

Hope this helps you out!