TypeScript Academy · Lesson

Publishing a Type Utility Library

Package and share custom utility types on npm.

Publishing a Type Utility Library is a free TypeScript Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the TypeScript Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

What Is a Type Utility Library?

A type utility library exports only TypeScript types — no runtime code. Popular examples include type-fest, ts-essentials, and utility-types.

// A type utility library exports types like:
export type DeepPartial<T> = T extends object
  ? { [K in keyof T]?: DeepPartial<T[K]> }
  : T;

Project Structure

Keep it simple: a single src/index.ts that re-exports all utilities, with tsconfig.json configured to emit declarations only.

// tsconfig.json
{
  "compilerOptions": {
    "declaration": true,
    "emitDeclarationOnly": true,
    "outDir": "dist",
    "strict": true
  }
}

package.json for a Types-Only Package

Set main and types fields to point to your declarations. Set sideEffects: false for tree-shaking.

{
  "name": "@myorg/type-utils",
  "version": "1.0.0",
  "main": "dist/index.js",
  "types": "dist/index.d.ts",
  "sideEffects": false,
  "files": ["dist"]
}

Generating Declarations

Run tsc to emit .d.ts files. For a types-only library, the JS output is empty or minimal.

# Build declarations
npx tsc
# dist/index.d.ts is generated

Versioning and Changelogs

Follow semantic versioning: breaking type changes are major, new utilities are minor, fixes are patch.

# Bump version
npm version minor
# Generate changelog with conventional-changelog or changesets

Publishing to npm

Use npm publish or pnpm publish. For scoped packages under an org, ensure you are logged in and the scope is set.

npm login
npm publish --access public
# or for private: npm publish --access restricted

TypeScript Version Compatibility

Document the minimum TypeScript version your utilities require. Recursive conditional types require TS 4.1+, Awaited is built-in from TS 4.5+.

// package.json peerDependencies
{
  "peerDependencies": {
    "typescript": ">=4.5"
  }
}

Testing Types with tsd

Use the tsd package to write type-level tests that run during CI to ensure your utilities behave correctly.

import { expectType } from "tsd";
import type { DeepPartial } from "@myorg/type-utils";

expectType<DeepPartial<{ a: { b: number } }>>({ a: {} });

Documentation with TSDoc

Add /** */ JSDoc comments to your types. Tools like TypeDoc generate API documentation from them.

/**
 * Makes all properties of T optional at every depth.
 * @example type A = DeepPartial<{ x: { y: number } }> // { x?: { y?: number } }
 */
export type DeepPartial<T> = ...

Monorepo Distribution

In a monorepo, publish the types package as a workspace package so other apps consume it via workspace:* instead of npm.

// Other package's package.json
{
  "dependencies": {
    "@myorg/type-utils": "workspace:*"
  }
}

Recap: Publishing Type Libraries

A type utility library: emitDeclarationOnly: true, exports types from src/index.ts, versioned with semver, tested with tsd, documented with TSDoc, published to npm or a workspace registry.

Quick Check

What tsconfig option generates only .d.ts files with no JavaScript output?

What You Learned

Publishing a type utility library requires emitDeclarationOnly, proper package.json fields, type-level tests with tsd, TSDoc comments, and semantic versioning. Share your utilities with the community or across your monorepo.

Frequently asked questions

Is the “Publishing a Type Utility Library” lesson free?

Yes — the full text of “Publishing a Type Utility Library” is free to read here on the web, and the TypeScript Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the TypeScript Academy course, upgrade to CoddyKit PRO.

What will I learn in “Publishing a Type Utility Library”?

Package and share custom utility types on npm. You practise TypeScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start TypeScript Academy?

No prior experience is required. TypeScript Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Publishing a Type Utility Library” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this TypeScript Academy lesson?

Yes. Every TypeScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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