How To Create And Publish Your JavaScript Library With SvelteKit

Table of Contents

• Node Package Manager
• Creating Your First Package
• Testing Your Package
• Publishing Your Package
• Unpublishing Your Package
• Using SvelteKit To Package Libraries

Node Package Manager

In case you didn’t know, npm is the package manager for Node.js.

The npm registry is a public collection of packages of open-source code for Node.js, front-end web apps, mobile apps, robots, routers, and countless other needs of the JavaScript community.

npm is the command line client that allows developers to install and publish those packages.

In this post I’m going to explain the basics of publishing a package to npm, and how using SvelteKit can make testing, packaging and publishing a Svelte, or JavaScript library to npm easier.

Creating Your First Package

You can publish any piece of code to npm, from simple utility functions, to libraries, and frameworks, so don’t think of npm as this serious thing (you only have to look at is-odd with 300,000+ monthly downloads 😂).

The only thing you have to do is sign up for an account on npm.

After you’re done, let’s start by creating your first package.

You can use npm init, which is going to prompt you to answer questions related to your package, and create a package.json file.

npm init

I’m going to create a basic package.json file instead, because most package.json fields aren’t relevant to us.

The only important field inside package.json is the name of the package, and the version number.

{
  "name": "greet",
	"version": "0.0.1",
	"main": "index.js",
	"type": "module"
}

You should respect semantic versioning when updating your package, but it’s not enforced by npm.

If you have a build step, you can change the main entry point of your program from index.js, to another path, such as dist/index.js.

To use the modern JavaScript import syntax, you have to specify that the type of your package is a module.

Create and export a simple greet function from index.js.

export function greet() {
	console.log('hi')
}

You can run the script with node index.js.

It would be easier if you could import greet inside of another project as a regular package, to make sure it works.

Testing Your Package

Create a test folder with a package.json file, which also needs to be a module to work with the greet package.

To test a package, you can use npm link, which links a package globally, and lets you use it anywhere.

Inside the greet package folder, run npm link to create a global link to the greet package.

npm link

You can run npm ls --link --global to see your linked packages.

└── greet@0.0.1 -> ./../../../../../greet

To link the greet package in test, run npm link greet, which is going to link the greet package inside node_modules.

npm link greet

You can use greet like a regular package inside test/index.js.

import { greet } from 'greet'

greet() // "hi"

You can run npm unlink greet, to remove the linked package from test.

npm unlink greet

To completely remove the package, run npm uninstall -g greet.

npm uninstall -g greet

If you use pnpm, you can use pnpm link where pnpm link -g creates a link to a package, and pnpm link -g greet links the package.

Publishing Your Package

To publish a package to npm, run npm publish (if you aren’t signed in to npm, you’re going to be prompted to do so).

npm publish

You might run into this problem.

403 Forbidden
PUT https://registry.npmjs.org/greet
You do not have permission to publish "greet".

This package already exists!

You can rename the package to something more unique, but it’s easier to scope the package to an organization, by creating an organization on npm.

Use the name of the organization you created.

{
	"name": "@joyofcode/greet",
	"version": "0.0.1",
	"main": "index.js",
	"type": "module"
}

If you try to publish the package now, it won’t work because scoped packages are private by default, which is a paid feature of npm.

 402 Payment Required
 PUT https://registry.npmjs.org/@joyofcode%2fgreet
 You must sign up for private packages.

You have to pass the --access=public flag, to make your package public.

npm publish --access=public

Your package is now available on npm, and ready to be installed.

Publishing to https://registry.npmjs.org/ with tag latest and public access
+ @joyofcode/test@0.0.1

Congrats! 🎉

Unpublishing Your Package

You have 72 hours to unpublish your package from npm.

npm unpublish @joyofcode/greet -f

This is because someone in the past removed left-pad, and broke the internet, so npm decided to not let anyone delete a package someone depends on anymore.

Using SvelteKit To Package Libraries

In most cases your library isn’t this simple, and you want things like TypeScript, testing, linting and formatting, which is a pain to set up.

Not only does SvelteKit make this easy, but you can run the package command to package the src/lib contents into a dist directory, with your transpiled JavaScript files, and generated types.

To get started, run npm create svelte, pick the library template, and select the options you want.

┌  Welcome to SvelteKit!
│
◇ Where should we create your project?
│  (hit Enter to use current directory)
│
◇ Which Svelte app template?
│  Library project
│
◇ Add type checking with TypeScript?
│  Yes, using TypeScript syntax
│
◆ Select additional options (use arrow
keys/space bar)
│  ◻ Add ESLint for code linting
│  ◻ Add Prettier for code formatting
│  ◻ Add Playwright for browser testing
│  ◻ Add Vitest for unit testing
└

Using the library template, src/lib becomes the main part of your app, and src/routes can be used for testing, and documentation.

Everything is already set up inside package.json, which you can learn more about in the SvelteKit docs.

The most important fields are exports and files:

• exports helps TypeScript and Svelte tooling know what to do
• files is to let npm know what files to upload, and which ones to ignore

{
	"exports": {
		".": {
			"types": "./dist/index.d.ts",
			"svelte": "./dist/index.js"
		}
	},
	"files": [
		"dist",
		"!dist/**/*.test.*",
		"!dist/**/*.spec.*"
	]
}

If you’re not publishing a Svelte library, rename the svelte field to default.

{
	"exports": {
		".": {
			"types": "./dist/index.d.ts",
			"default": "./dist/index.js"
		}
	}
}

You can link and test your package the same way as before with npm link. If you’re satisfied with everything, run npm run package to package your library.

npm run package

This is going to create a dist folder at the root.

To publish the package, run npm publish, or npm publish --access=public if you have a scoped package. You can build your docs with npm run build, and host it anywhere, like any regular SvelteKit site.

That’s it! 😄