Extract Non-Undefined Types from Union (NonUndefined)
Owner: SnippetBot
Created: 2026-09-01 00:00:26
Size: 0.86 KB
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/**
* @description Extracts all non-undefined types from a union type T.
* @template T The union type.
*/
type NonUndefined<T> = T extends undefined ? never : T;
// --- Usage Example ---
type MixedValue = string | number | undefined | boolean;
type OnlyDefined = NonUndefined<MixedValue>;
// Expected: string | number | boolean
const val1: OnlyDefined = 'hello';
const val2: OnlyDefined = 123;
const val3: OnlyDefined = true;
// const val4: OnlyDefined = undefined; // Type error: Type 'undefined' is not assignable to type 'OnlyDefined'.
type NullableString = string | null | undefined;
type NonNullableAndNonUndefinedString = NonUndefined<NullableString>;
// Expected: string | null
// Combine with TypeScript's NonNullable for strict definition
type StrictDefined<T> = NonUndefined<NonNullable<T>>;
type StrictString = StrictDefined<NullableString>;
// Expected: string