How to test npm packages locally

If you’ve ever created an npm package, you’ve most likely had the following question: “How can I be sure my package really works?”

You might have tests, but you’re not sure the code will work when installed.

You might have tests, but you’re not sure the code will work when once you install the package.

You could just publish your package and hope for the best. But, this is not really a great way to test. What if there’s a bug, or you need to debug some code?

Every time you make a change, you need to publish a new version to npm. This gets out of hand quickly, and you risk users installing broken packages.

Luckily, yalc solves this.

The Solution

With yalc we can publish packages locally and other projects can install the local version of your package.

Using yalc is easy. It takes 2 steps:

Publish the package locally
Install it

Optional: Push updates when you need to make changes.

Publish

First, publish the package locally.

npx yalc publish

This saves your package to a local store on your computer.

Install

Now add the package to your project. Go to your project folder and run:

npx yalc add my-package

You’ll see a .yalc folder. That’s where your package is.

Note: Add .yalc and yalc.lock to .gitignore. Don’t commit them.

Push updates

Sometimes, you find out that there’s a bug in the package. You go back to the package’s source code, make your tweaks, and run the build command.

Now you need to push your changes so that you can see the updated version inside the other projects.

npx yalc push

Note: If you’re using Vite, it might not pick up the changes. To fix that, run: rm -rf node_modules/.vite

This updates all projects using your local package at once.