How to Create, Test, and Publish an NPM Package with TypeScript

If you are a Node.js developer, you use 3rd-party packages in your day-to-day projects.

But… do you know how to create your own NPM package?

In this article, I’m going to demonstrate how to:

• create
• test
• publish

your own NPM package: string-manipulate

🚀 1. Create a New NPM Project

mkdir string-manipulate
cd string-manipulate
npm init -y

This generates a basic package.json file

📦 2. Add TypeScript to the Project

Install TypeScript and types for Node:

npm install typescript --save-dev
npm install @types/node --save-dev

Initialize TypeScript:

npx tsc --init

Update tsconfig.json to ensure proper module resolution for publishing:

{
  "compilerOptions": {
    "target": "ES2017",
    "module": "CommonJS",
    "declaration": true,
    "outDir": "./dist",
    "strict": true
  },
  "include": ["src"]
}

📁 3. Add Your Source Code

Create the folder structure:

mkdir src

Create your main file: src/index.ts

export function reverse(str: string): string {
  return str.split("").reverse().join("");
}

export function capitalize(str: string): string {
  if (!str) return "";
  return str[0].toUpperCase() + str.slice(1);
}

🧪 4. Add Tests (Optional but Recommended)

Let's use Jest.
Install Jest with TypeScript support:

npm install --save-dev jest ts-jest @types/jest

Initialize Jest config:

npx ts-jest config:init

Create a test: tests/index.test.ts

import { reverse, capitalize } from "../src";

test("reverse string", () => {
  expect(reverse("hello")).toBe("olleh");
});

test("capitalize string", () => {
  expect(capitalize("hello")).toBe("Hello");
});

Run tests:

npm test

🛠 5. Build the Project

Add this script to package.json:

"scripts": {
  "build": "tsc",
  "test": "jest"
}

Now run:

npm run build

This generates compiled files in dist/

📤 6. Prepare for Publishing

Update your package.json:

{
  "name": "string-manipulate",
  "version": "1.0.0",
  "main": "dist/index.js",
  "types": "dist/index.d.ts",
  "files": [
    "dist"
  ],
  "scripts": {
    "build": "tsc",
    "test": "jest"
  }
}

The "types" field allows TypeScript users to automatically get typings.

7. Use your package locally before publishing

run:

npm link

This makes your package available globally as a symlink.
Now, you can install it in your local machine:

npm link string-manipulate

🔄 When you make changes
You only need to run:

npm run build

in your package
The link updates automatically.

🔑 8. Login to NPM

npm login

Follow the prompts.

📦 9. Publish the Package

Before publishing, build again:

npm run build

publish:

npm publish

🎉 Congratulations — your TypeScript-ready NPM package is live!

🎯 10. Using the Package

Anyone can now install it via:

npm install string-manipulate

Example usage:

import { reverse, capitalize } from "string-manipulate";

console.log(reverse("hello")); // olleh
console.log(capitalize("hello")); // Hello

📚 Final Thoughts

Publishing your own package is a great way to share utilities across projects — or even with the world. With TypeScript support built in, your users get type safety and better DX out of the box.

If you'd like, I can also help you:

• ✅ add GitHub Actions for auto-publishing
• ✅ configure semantic-release
• ✅ create a README template

Just ask!