caseparser

CaseParser

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 and JSR
• Tree-shakeable

Note:

If you're looking for version 1.x.x, click here to see the docs.

Installation

npm add caseparser    # or: pnpm add caseparser / yarn add caseparser

Deno (JSR)

deno add jsr:@nandomb/caseparser

import { camelToSnake } from '@nandomb/caseparser';

Bun / Node.js from JSR

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	4.1+ (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/.

How to use

import { camelToSnake } from 'caseparser';      // ESM
// const { camelToSnake } = require('caseparser'); // CommonJS

camelToSnake('helloWorld'); // 'hello_world'

camelToSnake({ 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.

Typical use: API responses

import { snakeToCamel, camelToSnake } from 'caseparser';

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

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

Type inference

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

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

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

Conversion Types

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

All 56 functions:

• camelCase: camelToPascal, camelToSnake, camelToDash, camelToUpperSnake, camelToUpperDash, camelToTrain, camelToDot
• PascalCase: pascalToCamel, pascalToSnake, pascalToDash, pascalToUpperSnake, pascalToUpperDash, pascalToTrain, pascalToDot
• snake_case: snakeToCamel, snakeToPascal, snakeToDash, snakeToUpperSnake, snakeToUpperDash, snakeToTrain, snakeToDot
• dash-case: dashToCamel, dashToPascal, dashToSnake, dashToUpperSnake, dashToUpperDash, dashToTrain, dashToDot
• UPPER_SNAKE_CASE: upperSnakeToCamel, upperSnakeToPascal, upperSnakeToSnake, upperSnakeToDash, upperSnakeToUpperDash, upperSnakeToTrain, upperSnakeToDot
• UPPER-DASH-CASE: upperDashToCamel, upperDashToPascal, upperDashToSnake, upperDashToDash, upperDashToUpperSnake, upperDashToTrain, upperDashToDot
• Train-Case: trainToCamel, trainToPascal, trainToSnake, trainToDash, trainToUpperSnake, trainToUpperDash, trainToDot
• dot.case: dotToCamel, dotToPascal, dotToSnake, dotToDash, dotToUpperSnake, dotToUpperDash, dotToTrain

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 split letter by letter, because every uppercase letter starts a new word: camelToSnake('userID') → 'user_i_d'. Prefer userId style keys.
• Train-Case words are lowercased before converting, so trainToCamel('X-API-Key') → 'xApiKey'.
• Numbers are not word boundaries: camelToSnake('html5Parser') → 'html5_parser', snakeToCamel('user_1_name') → 'user1Name'.

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, so every published version can be traced back to the exact commit and workflow that built it. On npm, new versions are staged and only go live after a maintainer approves them with 2FA.

Found a vulnerability? Please report it privately, see SECURITY.md.

License

MIT © 2017 Fernando Machado Bernardino