How To Create An NPM Package

In this guide, we'll go through every single step you need to take to publish a package to npm.

This is not a minimal guide. We'll be setting up a fully production-ready package from an empty directory. This will include:

• Git for version control
• TypeScript for writing our code and keeping it type-safe
• Prettier for formatting our code
• @arethetypeswrong/cli for checking our exports
• tsup for compiling our TypeScript code into CJS and ESM
• Vitest for running our tests
• GitHub Actions for running our CI process
• Changesets for versioning and publishing our package

If you want to see the finished product, check out this demo repo.

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Video

If you prefer video content, I've created a video walkthrough of this guide:

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1. Git

In this section, we'll create a new git repository, set up a .gitignore, create an initial commit, create a new repository on GitHub, and push our code to GitHub.

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1.1: Initialize the repo

Run the following command to initialize a new git repository:

git init

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1.2: Set up a .gitignore

Create a .gitignore file in the root of your project and add the following:

node_modules

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1.3: Create an initial commit

Run the following command to create an initial commit:

git add .
git commit -m "Initial commit"

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1.4: Create a new repository on GitHub

Using the GitHub CLI, run the following command to create a new repository. I've chosen the name tt-package-demo for this example:

gh repo create tt-package-demo --source=. --public

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1.5: Push to GitHub

Run the following command to push your code to GitHub:

git push --set-upstream origin main

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2: package.json

In this section, we'll create a package.json file, add a license field, create a LICENSE file, and add a README.md file.

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2.1: Create a package.json file

Create a package.json file with these values:

{
  "name": "tt-package-demo",
  "version": "1.0.0",
  "description": "A demo package for Total TypeScript",
  "keywords": ["demo", "typescript"],
  "homepage": "https://github.com/mattpocock/tt-package-demo",
  "bugs": {
    "url": "https://github.com/mattpocock/tt-package-demo/issues"
  },
  "author": "Matt Pocock <team@totaltypescript.com> (https://totaltypescript.com)",
  "repository": {
    "type": "git",
    "url": "git+https://github.com/mattpocock/tt-package-demo.git"
  },
  "files": ["dist"],
  "type": "module"
}

• name is the name by which people will install your package. It must be unique on npm. You can create organization scopes (such as @total-typescript/demo) for free, these can help make it unique.
• version is the version of your package. It should follow semantic versioning: the 0.0.1 format. Each time you publish a new version, you should increment this number.
• description and keywords are short descriptions of your package. They're listed in searches in the npm registry.
• homepage is the URL of your package's homepage. The GitHub repo is a good default, or a docs site if you have one.
• bugs is the URL where people can report issues with your package.
• author is you! You can add optionally add your email and website. If you have multiple contributors, you can specify them as an array of contributors with the same formatting.
• repository is the URL of your package's repository. This creates a link on the npm registry to your GitHub repo.
• files is an array of files that should be included when people install your package. In this case, we're including the dist folder. README.md, package.json and LICENSE are included by default.
• type is set to module to indicate that your package uses ECMAScript modules, not CommonJS modules.

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2.2: Add the license field

Add a license field to your package.json. Choose a license here. I've chosen MIT.

{
  "license": "MIT"
}

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2.3: Add a LICENSE file

Create a file called LICENSE (no extension) containing the text of your license. For MIT, this is:

MIT License

Copyright (c) [year] [fullname]

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Change the [year] and [fullname] placeholders to the current year and your name.

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2.4: Add a README.md file

Create a README.md file with a description of your package. Here's an example:

**tt-package-demo**

A demo package for Total TypeScript.

This will be shown on the npm registry when people view your package.

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3: TypeScript

In this section, we'll install TypeScript, set up a tsconfig.json, create a source file, create an index file, set up a build script, run our build, add dist to .gitignore, set up a ci script, and configure our tsconfig.json for the DOM.

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3.1: Install TypeScript

Run the following command to install TypeScript:

npm install --save-dev typescript

We add --save-dev to install TypeScript as a development dependency. This means it won't be included when people install your package.

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3.2: Set up a tsconfig.json

Create a tsconfig.json with the following values:

{
  "compilerOptions": {
    /* Base Options: */
    "esModuleInterop": true,
    "skipLibCheck": true,
    "target": "es2022",
    "allowJs": true,
    "resolveJsonModule": true,
    "moduleDetection": "force",
    "isolatedModules": true,
    "verbatimModuleSyntax": true,

    /* Strictness */
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true,

    /* If transpiling with TypeScript: */
    "module": "NodeNext",
    "outDir": "dist",
    "rootDir": "src",
    "sourceMap": true,

    /* AND if you're building for a library: */
    "declaration": true,

    /* AND if you're building for a library in a monorepo: */
    "declarationMap": true
  }
}

These options are explained in detail in my TSConfig Cheat Sheet.

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3.3: Configure your tsconfig.json for the DOM

If your code runs in the DOM (i.e. requires access to document, window, or localStorage etc), skip this step.

If your code doesn't require access to DOM API's, add the following to your tsconfig.json:

{
  "compilerOptions": {
    // ...other options
    "lib": ["es2022"]
  }
}

This prevents the DOM typings from being available in your code.

If you're not sure, skip this step.

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3.4: Create A Source File

Create a src/utils.ts file with the following content:

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

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3.5: Create An Index File

Create a src/index.ts file with the following content:

export { add } from "./utils.js";

The .js extension will look odd. This article explains more.

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3.6: Set up a build script

Add a scripts object to your package.json with the following content:

{
  "scripts": {
    "build": "tsc"
  }
}

This will compile your TypeScript code to JavaScript.

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3.7: Running Your Build

Run the following command to compile your TypeScript code:

npm run build

This will create a dist folder with your compiled JavaScript code.

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3.8: Add dist to .gitignore

Add the dist folder to your .gitignore file:

dist

This will prevent your compiled code from being included in your git repository.

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3.9: Set up a ci script

Add a ci script to your package.json with the following content:

{
  "scripts": {
    "ci": "npm run build"
  }
}

This gives us a quick shortcut for running all required operations on CI.

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4: Prettier

In this section, we'll install Prettier, set up a .prettierrc, set up a format script, run the format script, set up a check-format script, add the check-format script to our CI script, and run the CI script.

Prettier is a code formatter that automatically formats your code to a consistent style. This makes your code easier to read and maintain.

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4.1: Install Prettier

Run the following command to install Prettier:

npm install --save-dev prettier

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4.2: Set up a .prettierrc

Create a .prettierrc file with the following content:

{
  "semi": true,
  "singleQuote": true,
  "trailingComma": "all",
  "printWidth": 80,
  "tabWidth": 2
}

You can add more options to this file to customize Prettier's behavior. You can find a full list of options here.

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4.3: Set up a format script

Add a format script to your package.json with the following content:

{
  "scripts": {
    "format": "prettier --write ."
  }
}

This will format all files in your project using Prettier.

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4.4: Run the format script

Run the following command to format all files in your project:

npm run format

You might notice some files change. Commit them with:

git add .
git commit -m "Format code with Prettier"

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4.5: Set up a check-format script

Add a check-format script to your package.json with the following content:

{
  "scripts": {
    "check-format": "prettier --check ."
  }
}

This will check if all files in your project are formatted correctly.

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4.6: Adding to our CI script

Add the check-format script to your ci script in your package.json:

{
  "scripts": {
    "ci": "npm run build && npm run check-format"
  }
}

This will run the check-format script as part of your CI process.

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5: exports, main and @arethetypeswrong/cli

In this section, we'll install @arethetypeswrong/cli, set up a check-exports script, run the check-exports script, set up a main field, run the check-exports script again, set up a ci script, and run the ci script.

@arethetypeswrong/cli is a tool that checks if your package exports are correct. This is important because these are easy to get wrong, and can cause issues for people using your package.

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5.1: Install @arethetypeswrong/cli

Run the following command to install @arethetypeswrong/cli:

npm install --save-dev @arethetypeswrong/cli

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5.2: Set up a check-exports script

Add a check-exports script to your package.json with the following content:

{
  "scripts": {
    "check-exports": "attw --pack ."
  }
}

This will check if all exports from your package are correct.

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5.3: Run the check-exports script

Run the following command to check if all exports from your package are correct:

npm run check-exports

You should notice various errors:

┌───────────────────┬──────────────────────┐
│                   │ "tt-package-demo"    │
├───────────────────┼──────────────────────┤
│ node10            │ 💀 Resolution failed │
├───────────────────┼──────────────────────┤
│ node16 (from CJS) │ 💀 Resolution failed │
├───────────────────┼──────────────────────┤
│ node16 (from ESM) │ 💀 Resolution failed │
├───────────────────┼──────────────────────┤
│ bundler           │ 💀 Resolution failed │
└───────────────────┴──────────────────────┘

This indicates that no version of Node, or any bundler, can use our package.

Let's fix this.

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5.4: Setting main

Add a main field to your package.json with the following content:

{
  "main": "dist/index.js"
}

This tells Node where to find the entry point of your package.

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5.5: Try check-exports again

Run the following command to check if all exports from your package are correct:

npm run check-exports

You should notice only one warning:

┌───────────────────┬──────────────────────────────┐
│                   │ "tt-package-demo"            │
├───────────────────┼──────────────────────────────┤
│ node10            │ 🟢                           │
├───────────────────┼──────────────────────────────┤
│ node16 (from CJS) │ ⚠️ ESM (dynamic import only) │
├───────────────────┼──────────────────────────────┤
│ node16 (from ESM) │ 🟢 (ESM)                     │
├───────────────────┼──────────────────────────────┤
│ bundler           │ 🟢                           │
└───────────────────┴──────────────────────────────┘

This is telling us that our package is compatible with systems running ESM. People using CJS (often in legacy systems) will need to import it using a dynamic import.

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5.6 Fix The CJS Warning

If you don't want to support CJS (which I recommend), change the check-exports script to:

{
  "scripts": {
    "check-exports": "attw --pack . --ignore-rules=cjs-resolves-to-esm"
  }
}

Now, running check-exports will show everything as green:

┌───────────────────┬───────────────────┐
│                   │ "tt-package-demo" │
├───────────────────┼───────────────────┤
│ node10            │ 🟢                │
├───────────────────┼───────────────────┤
│ node16 (from CJS) │ 🟢 (ESM)          │
├───────────────────┼───────────────────┤
│ node16 (from ESM) │ 🟢 (ESM)          │
├───────────────────┼───────────────────┤
│ bundler           │ 🟢                │
└───────────────────┴───────────────────┘

If you prefer to dual publish CJS and ESM, skip this step.

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5.7: Adding to our CI script

Add the check-exports script to your ci script in your package.json:

{
  "scripts": {
    "ci": "npm run build && npm run check-format && npm run check-exports"
  }
}

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6: Using tsup to Dual Publish

If you want to publish both CJS and ESM code, you can use tsup. This is a tool built on top of esbuild that compiles your TypeScript code into both formats.

My personal recommendation would be to skip this step, and only ship ES Modules. This makes your setup significantly simpler, and avoids many of the pitfalls of dual publishing, like Dual Package Hazard.

But if you want to, go ahead.

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6.1: Install tsup

Run the following command to install tsup:

npm install --save-dev tsup

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6.2: Create a tsup.config.ts file

Create a tsup.config.ts file with the following content:

import { defineConfig } from "tsup";

export default defineConfig({
  entryPoints: ["src/index.ts"],
  format: ["cjs", "esm"],
  dts: true,
  outDir: "dist",
  clean: true,
});

• entryPoints is an array of entry points for your package. In this case, we're using src/index.ts.
• format is an array of formats to output. We're using cjs (CommonJS) and esm (ECMAScript modules).
• dts is a boolean that tells tsup to generate declaration files.
• outDir is the output directory for the compiled code.
• clean tells tsup to clean the output directory before building.

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6.3: Change the build script

Change the build script in your package.json to the following:

{
  "scripts": {
    "build": "tsup"
  }
}

We'll now be running tsup to compile our code instead of tsc.

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6.4: Add an exports field

Add an exports field to your package.json with the following content:

{
  "exports": {
    "./package.json": "./package.json",
    ".": {
      "import": "./dist/index.js",
      "default": "./dist/index.cjs"
    }
  }
}

The exports field tells programs consuming your package how to find the CJS and ESM versions of your package. In this case, we're pointing folks using import to dist/index.js and folks using require to dist/index.cjs.

It's also recommended to add ./package.json to the exports field. This is because certain tools need easy access to your package.json file.

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6.5: Try check-exports again

Run the following command to check if all exports from your package are correct:

npm run check-exports

Now, everything is green:

┌───────────────────┬───────────────────┐
│                   │ "tt-package-demo" │
├───────────────────┼───────────────────┤
│ node10            │ 🟢                │
├───────────────────┼───────────────────┤
│ node16 (from CJS) │ 🟢 (CJS)          │
├───────────────────┼───────────────────┤
│ node16 (from ESM) │ 🟢 (ESM)          │
├───────────────────┼───────────────────┤
│ bundler           │ 🟢                │
└───────────────────┴───────────────────┘

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6.6: Turn TypeScript into a linter

We're no longer running tsc to compile our code. And tsup doesn't actually check our code for errors - it just turns it into JavaScript.

This means that our ci script won't error if we have TypeScript errors in our code. Eek.

Let's fix this.

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6.6.1: Add noEmit to tsconfig.json

Add a noEmit field to your tsconfig.json:

{
  "compilerOptions": {
    // ...other options
    "noEmit": true
  }
}

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6.6.2: Remove unused fields from tsconfig.json

Remove the following fields from your tsconfig.json:

• outDir
• rootDir
• sourceMap
• declaration
• declarationMap

They are no longer needed in our new 'linting' setup.

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6.6.3: Change module to Preserve

Optionally, you can now change module to Preserve in your tsconfig.json:

{
  "compilerOptions": {
    // ...other options
    "module": "Preserve"
  }
}

This means you'll no longer need to import your files with .js extensions. This means that index.ts can look like this instead:

export * from "./utils";

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6.6.4: Add a lint script

Add a lint script to your package.json with the following content:

{
  "scripts": {
    "lint": "tsc"
  }
}

This will run TypeScript as a linter.

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6.6.5: Add lint to your ci script

Add the lint script to your ci script in your package.json:

{
  "scripts": {
    "ci": "npm run build && npm run check-format && npm run check-exports && npm run lint"
  }
}

Now, we'll get TypeScript errors as part of our CI process.

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7: Testing with Vitest

In this section, we'll install vitest, create a test, set up a test script, run the test script, set up a dev script, and add the test script to our CI script.

vitest is a modern test runner for ESM and TypeScript. It's like Jest, but better.

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7.1: Install vitest

Run the following command to install vitest:

npm install --save-dev vitest

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7.2: Create a test

Create a src/utils.test.ts file with the following content:

import { add } from "./utils.js";
import { test, expect } from "vitest";

test("add", () => {
  expect(add(1, 2)).toBe(3);
});

This is a simple test that checks if the hello function returns the correct value.

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7.3: Set up test script

Add a test script to your package.json with the following content:

{
  "scripts": {
    "test": "vitest run"
  }
}

vitest run runs all tests in your project once, without watching.

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7.4: Run the test script

Run the following command to run your tests:

npm run test

You should see the following output:

 ✓ src/utils.test.ts (1)
   ✓ hello

 Test Files  1 passed (1)
      Tests  1 passed (1)

This indicates that your test passed successfully.

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7.5: Set up dev script

A common workflow is to run your tests in watch mode while developing. Add a dev script to your package.json with the following content:

{
  "scripts": {
    "dev": "vitest"
  }
}

This will run your tests in watch mode.

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7.6: Adding to our CI script

Add the test script to your ci script in your package.json:

{
  "scripts": {
    "ci": "npm run build && npm run check-format && npm run check-exports && npm run lint && npm run test"
  }
}

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8. Set up our CI with GitHub Actions

In this section, we'll create a GitHub Actions workflow that runs our CI process on every commit and pull request.

This is a crucial step in ensuring that our package is always in a working state.

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8.1: Creating our workflow

Create a .github/workflows/ci.yml file with the following content:

name: CI

on:
  pull_request:
  push:
    branches:
      - main

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

jobs:
  ci:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v4

      - name: Use Node.js
        uses: actions/setup-node@v4
        with:
          node-version: "20"

      - name: Install dependencies
        run: npm install

      - name: Run CI
        run: npm run ci

This file is what GitHub uses as its instructions for running your CI process.

• name is the name of the workflow.
• on specifies when the workflow should run. In this case, it runs on pull requests and pushes to the main branch.
• concurrency prevents multiple instances of the workflow from running at the same time, using cancel-in-progress to cancel any existing runs.
• jobs is a set of jobs to run. In this case, we have one job called ci.
• actions/checkout@v4 checks out the code from the repository.
• actions/setup-node@v4 sets up Node.js and npm.
• npm install installs the project's dependencies.
• npm run ci runs the project's CI script.

If any part of our CI process fails, the workflow will fail and GitHub will let us know by showing a red cross next to our commit.

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8.2: Testing our workflow

Push your changes to GitHub and check the Actions tab in your repository. You should see your workflow running.

This will give us a warning on every commit made, and every PR made to the repository.

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9. Publishing with Changesets

In this section, we'll install @changesets/cli, initialize Changesets, make changeset releases public, set commit to true, set up a local-release script, add a changeset, commit your changes, run the local-release script, and finally see your package on npm.

Changesets is a tool that helps you version and publish your package. It's an incredible tool that I recommend to anyone publishing packages to npm.

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9.1: Install @changesets/cli

Run the following command to initialise Changesets:

npm install --save-dev @changesets/cli

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9.2: Initialize Changesets

Run the following command to initialize Changesets:

npx changeset init

This will create a .changeset folder in your project, containing a config.json file. This is also where your changesets will live.

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9.3: Make changeset releases public

In .changeset/config.json, change the access field to public:

// .changeset/config.json
{
  "access": "public"
}

Without changing this field, changesets won't publish your package to npm.

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9.4: Set commit to true:

In .changeset/config.json, change the commit field to true:

// .changeset/config.json
{
  "commit": true
}

This will commit the changeset to your repository after versioning.

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9.5: Set up a local-release script

Add a local-release script to your package.json with the following content:

{
  "scripts": {
    "local-release": "changeset version && changeset publish"
  }
}

This script will run your CI process and then publish your package to npm. This will be the command you run when you want to release a new version of your package from your local machine.

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9.6 Run CI in prepublishOnly

Add a prepublishOnly script to your package.json with the following content:

{
  "scripts": {
    "prepublishOnly": "npm run ci"
  }
}

This will automatically run your CI process before publishing your package to npm.

This is useful to separate from the local-release script in case a user accidentally runs npm publish without running local-release. Thanks to Jordan Harband for the suggestion!

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9.7: Add a changeset

Run the following command to add a changeset:

npx changeset

This will open an interactive prompt where you can add a changeset. Changesets are a way to group changes together and give them a version number.

Mark this release as a patch release, and give it a description like "Initial release".

This will create a new file in the .changeset folder with the changeset.

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9.8: Commit your changes

Commit your changes to your repository:

git add .
git commit -m "Prepare for initial release"

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9.9: Run the local-release script

Run the following command to release your package:

npm run local-release

This will run your CI process, version your package, and publish it to npm.

It will have created a CHANGELOG.md file in your repository, detailing the changes in this release. This will be updated each time you release.

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9.10: See your package on npm

Go to:

http://npmjs.com/package/<your package name>

You should see your package there! You've done it! You've published to npm!

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Summary

You now have a fully set up package. You've set up:

• A TypeScript project with the latest settings
• Prettier, which both formats your code and checks that it's formatted correctly
• @arethetypeswrong/cli, which checks that your package exports are correct
• tsup, which compiles your TypeScript code to JavaScript
• vitest, which runs your tests
• GitHub Actions, which runs your CI process
• Changesets, which versions and publishes your package

For further reading, I'd recommend setting up the Changesets GitHub action and PR bot to automatically recommend contributors add changesets to their PR's. They are both phenomenal.

And if you've got any more questions, let me know!

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