Type alias HasUndefined<T, $O>

🎭 predicate

Validate if T is undefined or an union with undefined.

Example

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

type R = HasUndefined<number> // false
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🔢 customize

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

Example

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

type R = HasUndefined<number> // never
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🔢 customize

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

Example

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