Type Alias HasUndefined<T, $O>

HasUndefined: $ResolveBranch<
    $O,
    [IsUndefined<T> extends false ? $Else : $Then],
    T,
>

🎭 predicate

Validate if T is undefined or an union with undefined.

type R = HasUndefined<undefined> // true
type R = HasUndefined<undefined | 1> // true

type R = HasUndefined<number> // false

🔢 customize

Filter to ensure T is undefined or an union with undefined, otherwise returns never.

type R = HasUndefined<undefined> // undefined
type R = HasUndefined<undefined | 1> // undefined | 1

type R = HasUndefined<number> // never

🔢 customize

Use unique branch identifiers to allow precise processing of the result.

type R = HasUndefined<undefined, $SelectionBranch> // $Then
type R = HasUndefined<string, $SelectionBranch> // $Else