Type Alias MakeOptional<T, K>

MakeOptional: T extends T
? Omit<T, K> & Partial<Pick<T, Extract<K, keyof T>>>
: never

Makes specified keys K optional in each member of a union T.

This distributes over unions, ensuring each member is processed individually. Only keys that exist in each member are affected.

Type Parameters

T
The target type (can be a union)
K extends UnionKey<T> = UnionKey<T>
Keys to make optional (defaults to all union keys)

Example

type Result = MakeOptional<{ a: string; b: number }>;
//   ^?
// { a?: string; b?: number }

Example: Works with unions

type Result = MakeOptional<{ a: string } | { b: number }>;
//   ^?
// { a?: string } | { b?: number }

Example: Only make specific keys optional

type Result = MakeOptional<{ a: string } | { b: number }, "a">;
//   ^?
// { a?: string } | { b: number }