Crossposted on my blog
You can read here

In this blog post we create a small React library and publish it to NPM.

We'll go through all steps required to do that.

Let's begin.

Overview

The library we will publish (package from now on) is written in Typescript, bundled with tsup, versioned and published with changeset.

To test the package we create one example app with Next.js and one with Vite.

To better manage these three apps (our package + Next.js demo + Vite demo) we store everything in a monorepo, using turborepo.

The Package

It will be named use-last-visit-date and will contain a React hook used to:

Retrieve date of last visit, that was previously saved to localStorage.

Tutorial

1. Create a monorepo

This guide will not cover how a monorepo works, if this concept is new to you can read a little about it to get the idea.

If you want to skip that, you should know that for this guide i opted to monorepo only to be able to have the package itself and demo apps in the same codebase.

Otherwise i should have created 3 separate repo.

Let's go!

Setup

Tool used: turborepo, pnpm

To create a new monorepo, use create-turbo and follow the prompt.

NOTE:

If you don'have pnpm installed you can install it following installation guide

You can also use yarn or npm if you want.

# create a monorepo
npx create-turbo@latest

# answers
? Where would you like to create your turborepo? ./use-last-visit-date
? Which package manager do you want to use? pnpm

Turborepo will init the monorepo and print

>>> Created a new turborepo with the following:

 - apps/web: Next.js with TypeScript
 - apps/docs: Next.js with TypeScript
 - packages/ui: Shared React component library
 - packages/eslint-config-custom: Shared configuration (ESLint)
 - packages/tsconfig: Shared TypeScript `tsconfig.json`

>>> Success! Created a new Turborepo at "use-last-visit-date".

Good to know

turborepo expose an executable turbo that can fire a script in each workspace with a specific name.

For instance, running turbo build from root of monorepo will execute build script in every workspace.

If a workspace hasn't a build script, that workspace will be ignored.

In which order they are executed ?

turbo.json is the file where this configuration takes place.

Default setting will be enough for this guide, but i encourage you to read documentation later on.

Clean up

1. Rename root package.json name to "root-monorepo" to avoid collision with package we are going to create.

2. Delete apps/docs directory, we'll not use it

2. Create package workspace

To create our package run :

# go to root of the monorepo
cd ./use-last-visit-date

# create package directory
mkdir packages/use-last-visit-date
cd pacakges/use-last-visit-date

# init the package with pnpm
pnpm init

# install needed dev dependencies
pnpm add -D react react-dom @types/react @types/react-dom

Add tsconfig

We are using typescript so we need a tsconfig file.

Fortunately, turborepo already created a shared tsconfig internal package for us.

Inside there are various configuraion ready to be extended.

This is one of the beauties of using a tool like turborepo.

Add tsconfig as a dev dependency

# in packages/use-last-visit-date/package.json

"devDependencies": {
+  "tsconfig": "workspace:*",
}

Reinstall dependencies in whole monorepo

pnpm install

Create a tsconfig.json in packages/use-last-visit-date with this content

{
  "extends": "tsconfig/base.json",
  "include": ["."],
  "exclude": ["dist", "node_modules"],
  "compilerOptions": {
    "lib": ["dom", "dom.iterable", "esnext"]
  }
}

Write code

Create the file which will contain our code

# run this from packages/use-last-visit-date
touch ./index.ts

and fill with

import { useEffect, useState } from 'react';

const storage = {
  key: 'last-visit-date',
  save: (value: string) => window.localStorage.setItem(storage.key, value),
  retrieve: () => window.localStorage.getItem(storage.key) ?? null,
}

export const useLastVisitDate = () => {
  const [lastVisitDate, setLastVisitDate] = useState<null | string>(null);

  // On page load retrieve the last visit date if exists
  useEffect(() => {
    const value = storage.retrieve();
    setLastVisitDate(value);
  }, []);

  // On page close save current date
  useEffect(() => {
    const handler = () => {
      const currentDate = new Date().toISOString();
      storage.save(currentDate);
    }
    window.addEventListener('beforeunload', handler);
    return () => {
      window.removeEventListener('beforeunload', handler);
    }
  }, []);

  return lastVisitDate;
}

Then update which file will be exported by opening packages/use-last-visit-date/package.json and

- "main": "index.js",
+ "main": "./index.ts",

It's time to test our code in a real react app.

3. Create demo app workspace - Next

turborepo has already created a Next.js app in apps/web so there is no need to do it.

Because later on we will create also a Vite app, let's add a better name to this Next.js app.

Rename apps/web dir to apps/next and update apps/next/package.json :

- "name": "web",
+ "name": "next",

Then consume the useLastVisitDate hook in pages/index.tsx

const formatDate = (d: string) => {
  const date = new Date(d);
  return date.toLocaleString();
};

export default function Page() {
  const lastVisitDate = useLastVisitDate();

  return (
    <div>
      <h1>
        {lastVisitDate === null && "Hello, it's first time you visit us !"}
        {lastVisitDate && `Last Visit: ${formatDate(lastVisitDate)}`}
      </h1>
    </div>
  );
}

But this will throw an error because useLastVisitDate is not defined, and it's correct because we haven't imported it yet.

Before we can import it we must add the use-last-visit-date to dependencies of apps/next.

So update apps/next/package.json:

"dependencies": {
-  "ui": "workspace:*"
+  "use-last-visit-date": "workspace:*"
}

and tell pnpm to "refresh" monorepo dependencies by running

# is not important from "where" you run this command
pnpm install

Now you can import the hook in pages/index.tsx

// Add at the top
import { useLastVisitDate } from 'use-last-visit-date';

and errors should disappears.

NOTE:

If this is not happening, try Restarting TS server in your code editor.

Now it's time to test if it's working.

# run this from apps/next
pnpm dev

And open http://localhost:3000.

You should see

Hello, it's first time you visit us !

Then refresh the page and text should be changed to

Last Visit: ......

4. Create demo app workspace - Vite

Move with shell to root of monorepo and

# go to apps dir
cd apps

# create a vite workspace
pnpm create vite vite-react --template react-ts

# install dependencies
pnpm install

Then consume the useLastVisitDate hook in src/App.tsx

const formatDate = (d: string) => {
  const date = new Date(d);
  return date.toLocaleString();
};

export default function Page() {
  const lastVisitDate = useLastVisitDate();

  return (
    <div>
      <h1>
        {lastVisitDate === null && "Hello, it's first time you visit us !"}
        {lastVisitDate && `Last Visit: ${formatDate(lastVisitDate)}`}
      </h1>
    </div>
  );
}

But this will throw an error because useLastVisitDate is not defined, and it's correct because we haven't imported it yet.

Before we can import it we must add the use-last-visit-date to dependencies of apps/vite-react.

So update apps/vite-react/package.json:

"dependencies": {
  ...other-deps,
+  "use-last-visit-date": "workspace:*"
}

and tell pnpm to "refresh" monorepo dependencies by running

# is not important from "where" you run this command
pnpm install

Now you can import the hook in src/App.tsx

// Add at the top
import { useLastVisitDate } from 'use-last-visit-date';

and errors should disappears.

NOTE:

If this is not happening, try Restarting TS server in your code editor.

Now it's time to test if it's working.

# run this from apps/vite-react
pnpm dev

And open http://localhost:5173.

You should see

Hello, it's first time you visit us !

Then refresh the page and text should be changed to

Last Visit: ......

5. Time to publish

Overview

Now, use-last-visit-date is an internal packages, it's written in Typescript and it works because Next.js app and Vite app take care of compiling the code to js.

But our code should run also if these assumptions are not in place.

We need to compile to js.

Then we can publish to NPM.

To recap, publish a package to NPM consists of two steps:

• Bundle and compile source code to commonjs, so who install our packge will be able to import it
• Set up a dev script for local development.
• Publish to NPM
  • Control versioning
  • Control publishing

Bundle and Compile

Tools used: tsup

First, go with shell to packages/use-last-visit-date and

# install tsup as dev dependency
pnpm add -D tsup

# create a src dir
mkdir src

# move index.ts to src dir
mv index.ts src/index.ts

Then add a script to packages.json in packages/use-last-visit-date

{
  "scripts": {
+   "build": "tsup src/index.ts --format cjs --dts"
  }
}

This script,will use tsup to bundle and compile our code, and outputs files to the dist directory.

Because of that, you should:

• add dist to your .gitignore at root of monorepo to avoid push it when git pushing.
• update package.json main property, so who install this packages will use the bundled+compiled version of code.

# in packages/use-last-visit-date/package.json

- "main": "./index.ts",
+ "main": "./dist/index.js",
+ "types": "./dist/index.d.js",

Because this package is a react package, while developing we need react and react-dom installed as dev dependencies.

But we don't want to inject the whole react code inside our package when it's bundled and compiled.

What we want is to let consumer of package install it.

So, add peer dependencies to package.json in packages/use-last-visit-date

+  "peerDependencies": {
+      "react": ">=18.2.0",
+      "react-dom": ">=18.2.0"
+  },

Set up workflow for local development

Before adding tsup, apps inside apps directory was importing directly the source code file (with .ts extension).

So, when we updated the source code file, our apps received the updates.

Now we added a compile step in between, so we need to trigger a new build every time we update source code.

To do that, update package.json in packages/use-last-visit-date

{
  "scripts": {
    "build": "tsup src/index.ts --format cjs --dts"
+   "dev": "pnpm run build --watch"
  }
}

From now on, while developing, we'll use dev script.

Let's test a complete local development workflow.

Go to root of monorepo with shell and run

pnpm dev

This will trigger dev script of every workspace that has a dev script, in our case:

• packages/use-last-visit-date
• apps/next, available at http://localhost:3000
• apps/vite-react, available at http://localhost:5173

Try to change something in use-last-visit-date code and watch updates.

Publish to NPM

Every time you update source code, you want that this changes will be published as a new version.

You want also a place where to condense description of changes linked to every new version.

You can do it manually, but is very tedious and error prone.
Better to use a tool created for this.

This is when changeset enter the pitch.

Configure changeset

From root of the monorepo

# install changeset
pnpm add -w @changesets/cli

# setup
pnpm changeset init

Create 1.0.0 version

Set version to 0.0.1 in packages/use-last-visit-date/package.json

"version": "0.0.1"

Then use the versionig tool of changeset

# run this from root monorepo
pnpm changeset

# a prompt start

? Which packages would you like to include?
# select "use-last-visit-date" with arrows and space
# then press enter

? Which packages should have a major bump?
# select "use-last-visit-date" with arrows and space
# then press enter

? Are you sure you want to release the first major version of use-last-visit-date?
# confirm it

Please enter a summary for this change (this will be in the changelogs).
# write a description
# like "First release"
# then press enter

?Is this your desired changeset?
# confirm it

# bump version number
# running
pnpm changeset version

Now version should be 1.0.0.

Publish

Before publish check that every packages in your monorepo that MUST NOT be published has

"private": true

in its package.json.

This prevent them to be published to NPM.

Then update ./.changeset/config.json

- "access": "restricted",
+ "access": "public",

And....
Finally...
We can publish our package

pnpm changeset publish

Done!

Conclusion

I write articles mainly to help future myself or to help the growth of tools I use in my work.

If this article was helpful to you leave a like.

Would you like me to talk about a particular topic ?

Tell me in the comments !