Type Alias OptionalKeys<T>

OptionalKeys: {
    [K in keyof T]-?: {} extends Pick<T, K>
        ? K
        : undefined extends T[K] ? K : never
}[keyof T]

Extract the keys of optional properties.

Type Parameters

T
Object type to analyze

Remarks

Identifies properties that are optional in the object type, including properties whose value type explicitly allows undefined.

Example

type Obj = { a: number; b?: string; c: number | undefined; d: boolean };
type OptKeys = OptionalKeys< Obj >;  // 'b' | 'c'