TypeScript 7 reference · Utility Types

TypeScript Capitalize<StringType> Utility Type

Upper-case the first character of a string literal type: Capitalize<'click'> is 'Click'. Used to build names like onClick.

TypeScript 7 Since 4.1

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Syntax

Capitalize<StringType>

Parameter	Description
`StringType`	A string literal type.

The literal with its first letter upper-cased.

Event handler namesTry it yourself

type Event = "click" | "focus";
type Handler = `on${Capitalize<Event>}`; // "onClick" | "onFocus"
const h: Handler = "onFocus";
console.log(h);

Output

onFocus

Setter namesTry it yourself

type Field = "name" | "email";
type Setter = `set${Capitalize<Field>}`;
const setters: Setter[] = ["setName", "setEmail"];
console.log(setters);

Output

[ 'setName', 'setEmail' ]

Version	Change
TypeScript 4.1	Added

Uppercase<StringType> · Turn a string literal type into upper case at the type level: Uppercase<'get'> is 'GET'.
template literal types · Build string literal types with template syntax: `on${string}` or combinations of unions like `${Size}-${Color}`.
TypeScript Utility Types · tutorial