fs-helpers

Tree-shakeable utility functions: deep copy, type guards, and case conversion.

npm install @script-development/fs-helpers

What It Does

fs-helpers provides a small set of utility functions used across multiple packages and applications. Every function is individually importable — your bundler only includes what you use.

Deep Copy

Creates a deep clone of objects, arrays, and dates. Faster than structuredClone for typical application data:

import { deepCopy } from "@script-development/fs-helpers";

const original = {
  name: "Alice",
  roles: ["admin", "editor"],
  createdAt: new Date(),
};

const copy = deepCopy(original);
copy.roles.push("viewer");

original.roles; // ["admin", "editor"] — unchanged
copy.roles; // ["admin", "editor", "viewer"]

Writable Types

deepCopy returns a Writable<T> type — the same shape as the input but with all readonly modifiers removed. This is useful when you need a mutable copy of a readonly object:

interface User {
  readonly id: number;
  readonly name: string;
}

const user: User = { id: 1, name: "Alice" };
const mutable = deepCopy(user);
mutable.name = "Bob"; // allowed — Writable<User> removes readonly

Supported types

deepCopy handles primitives, plain objects, arrays, Date, and null. It does not handle Map, Set, RegExp, functions, or circular references. For those cases, use structuredClone.

Type Guards

isExisting

Checks whether an object has an id property — useful for distinguishing between new (unsaved) and existing (saved) domain objects:

import { isExisting } from "@script-development/fs-helpers";

interface User {
  id: number;
  name: string;
}

type NewUser = Omit<User, "id">;

function saveUser(user: User | NewUser) {
  if (isExisting(user)) {
    // TypeScript knows: user is User (has id)
    updateUser(user.id, user);
  } else {
    // TypeScript knows: user is NewUser (no id)
    createUser(user);
  }
}

Case Conversion

Convert between camelCase and snake_case with full type safety:

import { toCamelCaseTyped, deepCamelKeys, deepSnakeKeys } from "@script-development/fs-helpers";

toCamelCaseTyped

Converts a snake_case object to camelCase with preserved TypeScript types:

interface User {
  firstName: string;
  lastName: string;
  createdAt: string;
}

// API returns snake_case
const apiResponse = { first_name: "Alice", last_name: "Smith", created_at: "2026-01-01" };

const user = toCamelCaseTyped<User>(apiResponse);
// { firstName: "Alice", lastName: "Smith", createdAt: "2026-01-01" }
// Typed as User — not Record<string, unknown>

deepCamelKeys / deepSnakeKeys

Deep conversion for nested objects (re-exported from string-ts):

const apiData = {
  user_name: "Alice",
  user_settings: {
    dark_mode: true,
    font_size: 14,
  },
};

const camelData = deepCamelKeys(apiData);
// { userName: "Alice", userSettings: { darkMode: true, fontSize: 14 } }

const snakeData = deepSnakeKeys(camelData);
// Back to { user_name: "Alice", user_settings: { dark_mode: true, font_size: 14 } }

API Reference

Functions

Function	Signature	Description
deepCopy	<T>(toCopy: T) => Writable<T>	Deep clone for objects, arrays, dates
isExisting	<T extends {id: number}>(obj) => obj is T	Type guard for objects with an id
toCamelCaseTyped	<T extends object>(data) => T	Type-safe snake_case to camelCase
deepCamelKeys	(obj) => DeepCamelKeys	Deep snake_case to camelCase
deepSnakeKeys	(obj) => DeepSnakeKeys	Deep camelCase to snake_case

Types

Type	Description
Writable<T>	Removes all readonly modifiers from T
DeepSnakeKeys<T>	Recursively converts keys to snake_case