Type Alias IsStringLiteral<T>

IsStringLiteral: LiteralCheck<T, string>

Returns a boolean for whether the given type is a string literal type.

Useful for: - providing strongly-typed string manipulation functions - constraining strings to be a string literal - type utilities, such as when constructing parsers and ASTs

Type Parameters

  • T

Example

import type {IsStringLiteral} from 'type-fest';

type CapitalizedString<T extends string> = IsStringLiteral<T> extends true ? Capitalize<T> : string;

// https://github.com/yankeeinlondon/native-dash/blob/master/src/capitalize.ts
function capitalize<T extends Readonly<string>>(input: T): CapitalizedString<T> {
	return (input.slice(0, 1).toUpperCase() + input.slice(1)) as CapitalizedString<T>;
}

const output = capitalize('hello, world!');
//=> 'Hello, world!'

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