# 02.05.2022 - TypeScript / Build a library with Parcel

With Parcel 2.0, it’s very easy to build a TypeScript library and publish them to NPM later on, with automatically generated types and built-in support for both CommonJS and ESModule.

Let’s say you have a library file located at src/lib.ts:

export const sum = (a: number, b: number) => a + b;


You want to publish this library as an NPM package, so everyone can use it, all you have to do is modify your package.json to add the source, main, module, and types sections:

{
"name": "your-package-name",
"version": "1.0.0",
"source": "src/lib.ts",
"main": "dist/main.js",
"module": "dist/module.js",
"types": "dist/types.d.ts",
"devDependencies": {
"parcel": "^2.0.0",
"typescript": "^4.5.5"
}
}


The source field defines where your package’s entry point is.

The main field defines the main target of the build, which is the dist/main.js file.

The module field is to support ESModule.

And finally, the types field tells Parcel to generate a type definition .d.ts file for your library.

Run the build command:

npx parcel build


If everything went well, you can publish your package to NPM now.