MemberOfUnion
I am using the following type and have found it useful:
type MemberOfUnion<Union, Member> = Union extends Member | infer Inferred
? Inferred extends Union
? false
: true
: true;
type Test1 = MemberOfUnion<undefined | string, undefined>; // Result: true
type Test2 = MemberOfUnion<string | number, undefined>; // Result: false
type Test3 = MemberOfUnion<undefined, undefined>; // Result: true
type Test4 = MemberOfUnion<string, undefined>; // Result: false
type Test5 = MemberOfUnion<number, undefined>; // Result: false
type Test6 = MemberOfUnion<null | undefined, undefined>; // Result: true
type Test7 = MemberOfUnion<null, undefined>; // Result: false
type Test8 = MemberOfUnion<boolean | undefined, undefined>; // Result: true
type Test9 = MemberOfUnion<boolean, undefined>; // Result: false
type Test10 = MemberOfUnion<object | undefined, undefined>; // Result: true
type Test11 = MemberOfUnion<object, undefined>; // Result: false
type Test12 = MemberOfUnion<unknown | undefined, undefined>; // Result: false
type Test13 = MemberOfUnion<unknown, undefined>; // Result: false
sindresorhus / type-fest
A collection of essential TypeScript types
14.2k
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