# caseparser

> Convert Strings/Arrays/Objects from a type of case to another one.

Latest version **5.0.0** (published 2026-09-24) · MIT license · 0 weekly downloads

## Install

```sh
npm install caseparser
pnpm add caseparser
yarn add caseparser
bun add caseparser
```

## Health

**Score 75/100 (B)** — status: active.

Positive: has types; esm support; no vulnerabilities; has provenance; recently updated; high maintenance score; high quality score.

Warnings: low downloads.

## Facts

| | |
|---|---|
| Version | 5.0.0 |
| Published | 2026-09-24 |
| First published | 2017-09-06 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | ESM + CommonJS |
| Dependencies | 0 |
| Unpacked size | 309.5 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| Provenance | attested (GitHub Actions) |
| GitHub stars | 10 |
| Author | Fernando Machado Bernardino |
| Maintainers | nandomb |
| Keywords | caseparser, case parser, parser, convert, camel case, snake case, dash case, kebab case, constant case, header case, pascal case, upper snake case, upper dash case, train case, dot case, title case, sentence case, camelCase, snake_case, dash-case, kebab-case, PascalCase, UPPER_SNAKE_CASE, UPPER-DASH-CASE, Train-Case, dot.case, Title Case, Sentence case |

## Links

- npm: https://www.npmjs.com/package/caseparser
- Repository: https://github.com/NandoMB/caseparser
- Homepage: https://github.com/NandoMB/caseparser#readme
- Issues: https://github.com/NandoMB/caseparser/issues
- npm.io page: https://npm.io/package/caseparser

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## Recent versions

- 5.0.0 (latest) — 2026-09-24
- 4.3.0 — 2026-09-24
- 4.2.0 — 2026-09-24
- 4.1.0 — 2026-09-24
- 4.0.0 — 2026-09-23
- 3.0.0 — 2023-11-16
- 2.1.0 — 2023-04-10
- 2.0.3 — 2023-04-08
- 2.0.2 — 2023-04-05
- 2.0.1 — 2023-04-05
- 2.0.0-beta2 — 2023-04-05
- 1.1.0 — 2019-07-24
- 1.0.2 — 2018-03-12
- 1.0.1 — 2018-03-09
- 1.0.0 — 2017-09-06

## README

# [CaseParser](https://github.com/NandoMB/caseparser)

[![npm version](https://img.shields.io/npm/v/caseparser.svg)](https://www.npmjs.com/package/caseparser)
[![JSR](https://jsr.io/badges/@nandomb/caseparser)](https://jsr.io/@nandomb/caseparser)
[![JSR Score](https://jsr.io/badges/@nandomb/caseparser/score)](https://jsr.io/@nandomb/caseparser)
[![CI](https://github.com/NandoMB/caseparser/actions/workflows/main.yml/badge.svg)](https://github.com/NandoMB/caseparser/actions/workflows/main.yml)
[![npm downloads](https://img.shields.io/npm/dm/caseparser.svg)](https://www.npmjs.com/package/caseparser)
[![license](https://img.shields.io/npm/l/caseparser.svg)](./LICENSE)

Convert **Strings** and **JSON (Object Keys)** from a **case type** to another one with **type inference** based on parameter's type.

- Zero dependencies
- Written in TypeScript, published as ESM and CommonJS with type declarations
- Available on [npm](https://www.npmjs.com/package/caseparser) and [JSR](https://jsr.io/@nandomb/caseparser)
- Tree-shakeable


###### Note:
>  If you're looking for version 1.x.x, [click here](https://github.com/NandoMB/caseparser/tree/v1.x.x) to see the docs.


## Installation

```sh
npm add caseparser    # or: pnpm add caseparser / yarn add caseparser
```
###### Deno (JSR)
```sh
deno add jsr:@nandomb/caseparser
```
```ts
import { camelToSnake } from '@nandomb/caseparser';
```
###### Bun / Node.js from JSR
```sh
bunx jsr add @nandomb/caseparser
npx jsr add @nandomb/caseparser
```

## Compatibility

| Environment | Supported |
| --- | --- |
| ESM (`import`) | Node.js 12.22+, Deno, Bun, bundlers |
| CommonJS (`require`) | Node.js 8+, Bun |
| TypeScript | 4.5+ for the `toX` functions, 4.1+ for the deprecated `<from>To<To>` functions (any `moduleResolution`: `node`, `node16`/`nodenext`, `bundler`) |
| Browsers | Any ES2015 browser (via bundler) |
| Edge | Cloudflare Workers |

Every change is tested in CI on Node.js 22, 24 and 26, Bun, Deno, Cloudflare Workers, and in Chromium, Firefox and WebKit.

Ready-to-run projects for each environment (Node.js ESM/CommonJS, TypeScript, TypeScript 4.1, Bun, Deno, the browser and Cloudflare Workers) are in [examples/](./examples).

## How to use

```ts
import { toSnake } from 'caseparser';      // ESM
// const { toSnake } = require('caseparser'); // CommonJS

toSnake('helloWorld'); // 'hello_world'

toSnake({ firstName: 'John', addresses: [{ postalCode: '61105' }] });
// { first_name: 'John', addresses: [{ postal_code: '61105' }] }
```

Objects are converted deeply, including objects inside arrays. The input is never mutated: a new object is returned.

There is one function per target case, and the input can be in any case (see [From any case](#from-any-case)). Converting `'helloWorld'`:

| Function | Result | Also known as |
| --- | --- | --- |
| `toCamel` | `helloWorld` | lowerCamelCase |
| `toPascal` | `HelloWorld` | UpperCamelCase |
| `toSnake` | `hello_world` | |
| `toKebab` | `hello-world` | dash-case, param-case |
| `toUpperSnake` | `HELLO_WORLD` | CONSTANT_CASE, SCREAMING_SNAKE_CASE |
| `toUpperKebab` | `HELLO-WORLD` | COBOL-CASE, SCREAMING-KEBAB-CASE |
| `toTrain` | `Hello-World` | Header-Case |
| `toDot` | `hello.World` | dot.notation |
| `toTitle` | `Hello World` | Capital Case |
| `toSentence` | `Hello world` | |
| `toPascalSnake` | `Hello_World` | Ada_Case, Title_Snake_Case |
| `toPath` | `hello/World` | |
| `toSpace` | `hello World` | |
| `toLower` | `hello world` | no case |
| `toUpper` | `HELLO WORLD` | |

`toSpace`, `toPath` and `toDot` keep the original case of each word (`toPath('UserProfile')` → `'User/Profile'`); all the others lowercase the words first. To change the case of a whole string, use `toLowerCase()` or `toUpperCase()` on the result:

```ts
toPath('helloWorld');               // 'hello/World'
toPath('helloWorld').toLowerCase(); // 'hello/world'
toPath('helloWorld').toUpperCase(); // 'HELLO/WORLD'
```

Don't chain `toX` functions for this (`toUpper(toPath(...))`): each one splits its input into words again, so `/` and `.` would be treated as separators or symbols.

### Typical use: API responses

```ts
import { toCamel, toSnake } from 'caseparser';

const res = await fetch('/api/users/1');
const user = toCamel(await res.json());   // { firstName, lastName, ... }

await fetch('/api/users/1', {
  method: 'PUT',
  body: JSON.stringify(toSnake(user)),          // back to { first_name, ... }
});
```

### Type inference

The resulting keys are inferred at the type level, so your editor autocompletes the converted names:

```ts
const user = toCamel({ first_name: 'John', addresses: [{ postal_code: '61105' }] });
//    ^? { firstName: string; addresses: { postalCode: string }[] }

user.firstName;  // ✅
user.first_name; // ❌ Property 'first_name' does not exist
```

### From any case

You don't need to know the input's case: the input is split into words whatever its case, so keys in different cases can even be mixed in the same object:

```ts
import { toCamel, toSnake } from 'caseparser';

toSnake('helloWorld');  // 'hello_world'
toSnake('Hello World'); // 'hello_world'
toSnake('HELLO-WORLD'); // 'hello_world'

toCamel({ user_id: 1, 'Last-Name': 'Doe', XMLHttpRequest: true });
//    ^? { userId: number; lastName: string; xmlHttpRequest: boolean }
```

Words are split on `_`, `-`, `.` and spaces, and before an uppercase letter that starts a new word.

### Symbols

Symbols (ASCII punctuation such as `$`, `@`, `#` or `%`) are removed by default. Pass a second argument to keep them: `true` keeps all of them, and an array keeps only the listed ones:

```ts
toCamel({ $ref: 1, '@type': 'user' });         // { ref: 1, type: 'user' }
toCamel({ $ref: 1, '@type': 'user' }, true);   // { $ref: 1, '@type': 'user' }
toCamel({ $ref: 1, '@type': 'user' }, ['$']);  // { $ref: 1, type: 'user' }

toCamel('$Hello-world', true); // '$helloWorld'
toPascal('$id', true);         // '$Id'
```

A symbol always starts a new word, so the words are the same whether symbols are kept or not. A kept symbol sticks to the start of the next word, or to the end of the previous one when no word follows:

```ts
toSnake('$$hello$World$$hi');       // 'hello_world_hi'
toSnake('$$hello$World$$hi', true); // '$$hello_$world_$$hi'
toSnake('user@name', true);         // 'user_@name'
toSnake('total%_count', true);      // 'total%_count'
```

The inferred types follow the same rules. `_`, `-` and `.` are separators, not symbols, so `_links` always becomes `links`.

## Conversion Types

> **Deprecated:** the `<from>To<To>` functions below are deprecated in favor of the `toX` functions ([How to use](#how-to-use)) and will be removed in the next major version, which will also require TypeScript 4.7+. They keep working until then. See [Migrating to `toX`](#migrating-to-tox).

Every function is named `<from>To<To>`, e.g. `snakeToCamel`. The case names are:

| Name | Example |
| --- | --- |
| `camel` | `helloWorld` |
| `pascal` | `HelloWorld` |
| `snake` | `hello_world` |
| `dash` | `hello-world` |
| `upperSnake` | `HELLO_WORLD` |
| `upperDash` | `HELLO-WORLD` |
| `train` | `Hello-World` |
| `dot` | `hello.world` |
| `title` | `Hello World` |
| `sentence` | `Hello world` |

All 90 functions:

- **camelCase:** `camelToPascal`, `camelToSnake`, `camelToDash`, `camelToUpperSnake`, `camelToUpperDash`, `camelToTrain`, `camelToDot`, `camelToTitle`, `camelToSentence`
- **PascalCase:** `pascalToCamel`, `pascalToSnake`, `pascalToDash`, `pascalToUpperSnake`, `pascalToUpperDash`, `pascalToTrain`, `pascalToDot`, `pascalToTitle`, `pascalToSentence`
- **snake_case:** `snakeToCamel`, `snakeToPascal`, `snakeToDash`, `snakeToUpperSnake`, `snakeToUpperDash`, `snakeToTrain`, `snakeToDot`, `snakeToTitle`, `snakeToSentence`
- **dash-case:** `dashToCamel`, `dashToPascal`, `dashToSnake`, `dashToUpperSnake`, `dashToUpperDash`, `dashToTrain`, `dashToDot`, `dashToTitle`, `dashToSentence`
- **UPPER_SNAKE_CASE:** `upperSnakeToCamel`, `upperSnakeToPascal`, `upperSnakeToSnake`, `upperSnakeToDash`, `upperSnakeToUpperDash`, `upperSnakeToTrain`, `upperSnakeToDot`, `upperSnakeToTitle`, `upperSnakeToSentence`
- **UPPER-DASH-CASE:** `upperDashToCamel`, `upperDashToPascal`, `upperDashToSnake`, `upperDashToDash`, `upperDashToUpperSnake`, `upperDashToTrain`, `upperDashToDot`, `upperDashToTitle`, `upperDashToSentence`
- **Train-Case:** `trainToCamel`, `trainToPascal`, `trainToSnake`, `trainToDash`, `trainToUpperSnake`, `trainToUpperDash`, `trainToDot`, `trainToTitle`, `trainToSentence`
- **dot.case:** `dotToCamel`, `dotToPascal`, `dotToSnake`, `dotToDash`, `dotToUpperSnake`, `dotToUpperDash`, `dotToTrain`, `dotToTitle`, `dotToSentence`
- **Title Case:** `titleToCamel`, `titleToPascal`, `titleToSnake`, `titleToDash`, `titleToUpperSnake`, `titleToUpperDash`, `titleToTrain`, `titleToDot`, `titleToSentence`
- **Sentence case:** `sentenceToCamel`, `sentenceToPascal`, `sentenceToSnake`, `sentenceToDash`, `sentenceToUpperSnake`, `sentenceToUpperDash`, `sentenceToTrain`, `sentenceToDot`, `sentenceToTitle`

## Migrating to `toX`

Replace each `<from>To<To>` function with the `toX` function for its target case, whatever the source case: `camelToSnake`, `dashToSnake`, `titleToSnake`... all become `toSnake`. The dash cases were renamed: `<from>ToDash` becomes `toKebab`, and `<from>ToUpperDash` becomes `toUpperKebab`.

For well-formed keys (`firstName`, `first_name`) the result is the same. It differs when a key has consecutive uppercase letters or doesn't match the source case, and `toDot` keeps the original case of each word:

| Call | `<from>To<To>` result | `toX` result |
| --- | --- | --- |
| `camelToSnake('userID')` / `toSnake('userID')` | `'user_i_d'` | `'user_id'` |
| `camelToSnake('XMLHttpRequest')` / `toSnake('XMLHttpRequest')` | `'_x_m_l_http_request'` | `'xml_http_request'` |
| `camelToSnake('HelloWorld')` / `toSnake('HelloWorld')` | `'_hello_world'` | `'hello_world'` |
| `snakeToCamel('user_ID')` / `toCamel('user_ID')` | `'userID'` | `'userId'` |
| `camelToDot('helloWorld')` / `toDot('helloWorld')` | `'hello.world'` | `'hello.World'` |

If your code reads keys like `user_i_d` produced by the old functions, update those reads when migrating. The inferred types follow the new results, so TypeScript points out every place to change.

## Behavior and limitations

- **Only keys are converted, never values.** In `{ userName: 'johnDoe' }`, `userName` becomes `user_name` but `'johnDoe'` is kept. Strings inside arrays are kept too.
- **Only plain objects are traversed.** `Date`, `Map`, `Set` and class instances are returned as they are (same reference), without converting their contents.
- **Acronyms are kept together, but not restored:** `toSnake('userID')` → `'user_id'`, and back `toCamel('user_id')` → `'userId'`.
- **Words are lowercased** before converting (except by `toSpace`, `toPath` and `toDot`), so `toCamel('X-API-Key')` → `'xApiKey'` and `toCamel('First Name')` → `'firstName'`.
- **Title Case capitalizes every word**, including short ones: `toTitle('termsOfUse')` → `'Terms Of Use'`.
- **Digits stay attached to the previous word:** `toSnake('html5Parser')` → `'html5_parser'`, `toSnake('user1Name')` → `'user1_name'`.
- **Type inference has a key length limit.** TypeScript limits how deeply a type can recurse, and keys are converted character by character at the type level. The `toX` functions infer keys up to ~120 characters; longer keys fail to compile with `Type instantiation is excessively deep and possibly infinite`. The runtime conversion has no limit.

## Security

caseparser is safe to use with untrusted input (e.g. request bodies or `JSON.parse` output): keys such as `__proto__` are copied as regular keys and never change an object's prototype, and only the object's own properties are converted.

Releases are built and published from GitHub Actions without long-lived tokens (OIDC), with [npm provenance](https://docs.npmjs.com/generating-provenance-statements), so every published version can be traced back to the exact commit and workflow that built it. On npm, new versions are [staged](https://docs.npmjs.com/staged-publishing/) and only go live after a maintainer approves them with 2FA.

Found a vulnerability? Please report it privately, see [SECURITY.md](./SECURITY.md).

## License

[MIT](./LICENSE) © 2017 Fernando Machado Bernardino

---
_Source: https://npm.io/package/caseparser · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._