TypeScript 4.1 and type-fest 0.20.x brings eg. CamelCase<> capabilities

[voxpelli]

In type-fest v0.20.0 a PR of mine got merged that, together with the new TypeScript 4.1 release, enables new custom type helpers like CamelCase<>.

Disclaimer: Since that PR I'm now also a co-maintainer of type-fest. That doesn't make me less of a fan of the work @sindresorhus and others has put into it though, hence I want to share.

I've used CamelCase<> myself when working with database queries, where all columns have been snake-cased, and the rest of my code, where the same properties have been camel-cased.

Using CamelCase<> I created the following:

TypeScript-flavor:

export type CamelCasedProps<T> = { [K in keyof T as CamelCase<K>]: T[K] };

JSDoc-flavor:

/**
 * @template T
 * @typedef { { [K in keyof T as CamelCase<K>]: T[K] }} CamelCasedProps
 */

Which I could then use to convert the type of a database result to the type that my JS wants:

/**
 * @typedef DbResult
 * @property {string} full_name
 * @property {string} street_address
 */

/** @type {CamelCasedProps<DbResult>} */
const person = {
  fullName: 'Bob Bobson`,
  streetAddress: 'Infinite loop 1`
};

Nice to be able to get less repetition of types and more guarantees that two types actually match in everything but their property casing.

(And this is just one of the things that the template literal types in TypeScript 4.1 enables)