string-manipulation

`Capitalize<S>`

Intrinsic string type utility that uppercases the first character of literal string S, leaving the rest unchanged. Enables typed camelCase-to-PascalCase and getter-name construction.

Definition

type Capitalize<S extends string> = intrinsic

Usage patterns

Pattern	Purpose
Capitalize<'foo'>	Basic first-letter uppercase
`get${Capitalize<K>}`	Build getter names from field names
Capitalize<Uncapitalize<S>>	Normalize to a guaranteed capitalized form
Capitalize<K & string>	Narrow keyof T to strings before capitalizing

Examples

type C = Capitalize<'foo'>;

Result: 'Foo'

type Getters<T> = { [K in keyof T as `get${Capitalize<K & string>}`]: () => T[K] };

Generates getFoo, getBar, ... mapping from object keys

type U = 'apple' | 'banana';
type C = Capitalize<U>;

Result: 'Apple' | 'Banana' — distributes over unions

type S = Capitalize<string>;

Result: string when the input is not a literal

Gotcha

Only affects the FIRST character — the remainder is left as-is. Non-literal inputs widen to plain `string`.

Related utility types

Uncapitalize<S>

Intrinsic type utility that lowercases the first character of literal S, leaving the rest unchanged. The inverse of Capitalize and widely used for PascalCase-to-camelCase mappings.

Uppercase<S>

Compile-time intrinsic that converts a string literal type S to its uppercase form. Introduced in TS 4.1 alongside template literal types.

Lowercase<S>

Intrinsic string type manipulator that converts each character of literal S to lowercase. Available since TS 4.1 and evaluated by the compiler with no runtime cost.

Record<K, V>

Creates an object type whose keys come from the union K and whose values all have type V. Useful for lookup tables, dictionaries, and enum-keyed maps.

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