Type alias IsString<T, $O>

🎭 predicate

Validate if T is string or string literals.

Example

type R = IsString<string> // true
type R = IsString<'a'> // true

type R = IsString<never> // false
type R = IsString<unknown> // false
type R = IsString<string | boolean> // boolean
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🔢 customize

Filter to ensure T is string or string literals, otherwise returns never.

Example

type R = IsString<string, { selection: 'filter' }> // string
type R = IsString<'a', { selection: 'filter' }> // 'a'

type R = IsString<never, { selection: 'filter' }> // never
type R = IsString<unknown, { selection: 'filter' }> // never
type R = IsString<string | boolean, { selection: 'filter' }> // string
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🔢 customize:

Disable distribution of union types.

type R = IsString<string | 1> // boolean
type R = IsString<string | 1, { distributive: false }> // false
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🔢 customize

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

Example

type R = IsString<string, $IsString.$Branch> // $Then
type R = IsString<bigint, $IsString.$Branch> // $Else
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