Text Case Conversion in TypeScript – Type-Safe Guide
Published 2026-03-02 · convertcase.in
TypeScript inherits JavaScript's string methods but adds the ability to create strongly-typed case utilities. Here's how to build them.
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1Basic Methods
"HELLO".toLowerCase() → "hello" (type: string) "hello".toUpperCase() → "HELLO" (type: string)
2TypeScript Template Literal Types
TypeScript 4.1+ has built-in utility types: type Lower = Lowercase<"HELLO"> // "hello" type Upper = Uppercase<"hello"> // "HELLO" type Capitalized = Capitalize<"hello"> // "Hello"
3Type-Safe Case Converter
Build a function that accepts a union type of allowed case formats and returns correctly typed output.
Frequently Asked Questions
Does TypeScript have Capitalize and Uncapitalize types?
Yes — since TypeScript 4.1: Capitalize<T>, Uncapitalize<T>, Uppercase<T>, Lowercase<T> are built-in template literal types.