Typescript type camelCase / snake_case conversion

camelCase-snake_case-types.ts

type CamelCase<S extends string> = S extends `${infer P1}_${infer P2}${infer P3}`
? `${Lowercase<P1>}${Uppercase<P2>}${CamelCase<P3>}`
: Lowercase<S>

type KeysToCamelCase<T> = {
  [K in keyof T as CamelCase<string & K>]: T[K]
}


type CamelToSnakeCase<S extends string> = S extends `${infer T}${infer U}` ?
  `${T extends Capitalize<T> ? "_" : ""}${Lowercase<T>}${CamelToSnakeCase<U>}` :
  S

type KeysToSnakeCase<T> = {
[K in keyof T as CamelToSnakeCase<string & K>]: T[K]
}

This doesn't work for objects keys in arrays like this:

const data = {
  name: 'Rocket',
  parts: [ { brandName: 'starx' }]
}

Thanks for sharing!