polycase

A small, dependency-free, TypeScript-first toolkit for predictable string case conversion. Unicode-aware tokenization, 11 built-in cases, and a single toCase() dispatcher — in ~3 kB gzip.

Why polycase?

Most case-conversion libraries treat acronyms as opaque blobs or require manual configuration to split them. polycase recognizes acronym runs, numeric boundaries, and Unicode combining marks out of the box:

import { camelCase, tokenize, toCase } from "polycase";

// Acronym runs split correctly — no configuration needed
camelCase("getHTTPSUrl"); //=> "getHttpsUrl"
toCase("snake", "XMLParser"); //=> "xml_parser"

// Numeric boundaries detected automatically
toCase("kebab", "item3D"); //=> "item-3-d"

// Full Unicode support, including combining marks
tokenize("Cafe\u0301Noir"); //=> ["café", "noir"]  (NFC-normalized)

• Zero dependencies — nothing to audit, nothing to break
• ~3 kB gzip — ESM and CommonJS, with bundled types
• Predictable tokenization — separators, camelCase, PascalCase, acronym runs, and numeric boundaries all handled by one deterministic algorithm
• Idempotent — applying the same case twice always returns the same result

Quick start

npm install polycase
pnpm add polycase
yarn add polycase

import { camelCase, isCamelCase, titleCase, toCase, whichCases } from "polycase";

camelCase("hello world");
//=> "helloWorld"

titleCase("the lord of the rings");
//=> "The Lord of the Rings"

toCase("upper", "getHTTPSUrl", { separator: "." });
//=> "GET.HTTPS.URL"

isCamelCase("helloWorld");
//=> true

whichCases("HELLO_WORLD");
//=> ["constant"]

For the full API reference, see packages/polycase/README.md.

Supported cases

Case	Function	"helloWorld"	"getHTTPSUrl"
camel	camelCase	helloWorld	getHttpsUrl
capital	capitalCase	Hello World	Get Https Url
constant	constantCase	HELLO_WORLD	GET_HTTPS_URL
header	headerCase	Hello-World	Get-Https-Url
kebab	kebabCase	hello-world	get-https-url
lower	lowerCase	hello world	get https url
pascal	pascalCase	HelloWorld	GetHttpsUrl
sentence	sentenceCase	Hello world	Get https url
snake	snakeCase	hello_world	get_https_url
title	titleCase	Hello World	Get Https Url
upper	upperCase	HELLO WORLD	GET HTTPS URL

Repository structure

packages/polycase/   Published package — source, tests, and build output
config/              Shared build and lint configuration

Local development

pnpm install          # install all dependencies
pnpm build            # build the package
pnpm test             # run all tests (vitest)
pnpm lint             # check code style (oxlint)
pnpm format           # auto-format with prettier
pnpm typecheck        # run tsc --noEmit

Build or test the package in isolation:

pnpm --filter polycase build
pnpm --filter polycase test

Contributing

Contributions are very welcome — from docs and examples to bug fixes, new plugins and features.

Feedback & Issues

We’d love to hear your feedback — on API design, DX, docs, issues and ideas. Report them here.

License

Apache-2.0 — see LICENSE