Lowercase<StringType>

INFO

The Lowercase<StringType> utility type is available starting from TypeScript version 4.1. For more information see in TypeScript Handbook, Release Note

Overview

The Lowercase<StringType> utility type in TypeScript is used to convert each character in the string to the lowercase version.

Syntax

type Lowercase<S extends string> = intrinsic;

• StringType (S): The string that you want to convert each character in the string to the lowercase version.

Examples

Example #1

type Greeting = 'Hello, world';
type QuietGreeting = Lowercase<Greeting>; // 'hello, world'

type ASCIICacheKey<Str extends string> = `id-${Lowercase<Str>}`;
type MainID = ASCIICacheKey<'MY_APP'>; // 'id-my_app'

Example #2

type Environment = 'DATABASE_URL' | 'NODE_ENV' | 'PORT';
type LowercaseEnvironment = Lowercase<Environment>;

const env: Record<LowercaseEnvironment, string> = {
  database_url: 'mongodb://localhost:27017/db',
  node_env: 'development',
  port: '8000',
};