Type Alias UnionToIntersection<Union>

UnionToIntersection: (
    Union extends unknown ? (distributedUnion: Union) => void : never
) extends (mergedIntersection: infer Intersection) => void
    ? Intersection
    : never

Convert a union type to an intersection type using distributive conditional types.

Inspired by this Stack Overflow answer.

Type Parameters

  • Union
import type {UnionToIntersection} from 'type-fest';

type Union = {the(): void} | {great(arg: string): void} | {escape: boolean};

type Intersection = UnionToIntersection<Union>;
//=> {the(): void; great(arg: string): void; escape: boolean};

A more applicable example which could make its way into your library code follows.

import type {UnionToIntersection} from 'type-fest';

class CommandOne {
commands: {
a1: () => undefined,
b1: () => undefined,
}
}

class CommandTwo {
commands: {
a2: (argA: string) => undefined,
b2: (argB: string) => undefined,
}
}

const union = [new CommandOne(), new CommandTwo()].map(instance => instance.commands);
type Union = typeof union;
//=> {a1(): void; b1(): void} | {a2(argA: string): void; b2(argB: string): void}

type Intersection = UnionToIntersection<Union>;
//=> {a1(): void; b1(): void; a2(argA: string): void; b2(argB: string): void}