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

This works.

It accepts a generic type T, in your case a string.

The generic type OneOrMore defines either 1 of T or an array of T.

Your generic input object type Opts is either an object with either a key path of OneOrMore, or a key paths of OneOrMore. Although not really necessary, I made it explicit with that the only other option is never acceptable.

type OneOrMore = T | T[];

export type Opts = { path: OneOrMore } | { paths: OneOrMore } | never;

export const foo = (o: Opts) => {};

foo({});

There is an error with {}