Typescript type which allow to set a value only on one from listed fields.

OneOf.ts

/**
 * Make all properties in T optional except property with key U.
 *
 * @example
 *  type Example = OtherOptional<'a', { a: string; b: string; }> // { a: string; b?: never; }
 */
export type OtherOptional<U extends keyof T, T> = Pick<T, U> & Partial<T>;

/**
 * Make all properties in T disallowed (type never) except property with key U.
 *
 * @example
 *  type Example = OtherDisallowed<'a', { a: string; b: string; }> // { a: string; b: never; }
 */
export type OtherDisallowed<U extends keyof T, T> = { [K in keyof T]: K extends U ? T[K] : never };

/**
 * Make type that allows objects with only one property from type T and not the rest.
 *
 * @example
 * type Example = OneOf<{ red: string, green: string }> //{red: string; green?: never} | {red?: never; green: string}
 *
 *
 * const example: Example = { red: 'some text' green: 'some text' }
 *       ~~~~~~~
 * // error TS2322: Type '{ red: string; green: string; }' is not assignable to type 'Example1'.
 * // Type '{ red: string; green: string; }' is not assignable to type 'OtherDisallowed<"red", OtherOptional<"red", { red: string; green: string; }>>'.
 * //   Types of property 'green' are incompatible.
 * //     Type 'string' is not assignable to type 'never'.
 */
export type OneOf<T> = { [K in keyof T]: OtherDisallowed<K, OtherOptional<K, T>> }[keyof T];