es-toolkit/dist/types/ToSnakeCaseKeys.d.ts

A state-of-the-art, high-performance JavaScript utility library with a small bundle size and strong type annotations.

import { NonPlainObject } from "../_internal/NonPlainObject.js";

//#region src/types/ToSnakeCaseKeys.d.ts
type SnakeCase<S extends string> = S extends Uppercase<S> ? Lowercase<S> : S extends `${infer P1}${infer P2}` ? P2 extends Uncapitalize<P2> ? `${Lowercase<P1>}${SnakeCase<P2>}` : `${Lowercase<P1>}_${SnakeCase<Uncapitalize<P2>>}` : Lowercase<S>;
/**
 * Converts the keys of `T` to snake_case recursively.
 *
 * This is the return type of the `toSnakeCaseKeys` function. Recurses into
 * plain objects and arrays; built-in objects like `Date`, `Map`, and functions
 * pass through unchanged.
 *
 * @template T - The type whose keys are converted.
 *
 * @example
 * type Request = { userId: number; firstName: string };
 * type Converted = ToSnakeCaseKeys<Request>;
 * // => { user_id: number; first_name: string }
 */
type ToSnakeCaseKeys<T> = T extends NonPlainObject ? T : T extends any[] ? Array<ToSnakeCaseKeys<T[number]>> : T extends Record<string, any> ? { [K in keyof T as SnakeCase<string & K>]: ToSnakeCaseKeys<T[K]> } : T;
//#endregion
export { ToSnakeCaseKeys };