At Spatie we're constantly improving our application template called Blender. We love using packages to pull in functionality. Creating and using packages has many benefits. Though we try to create public packages that benefit the community, there are some packages that are very specific to Blender. Public repositories such as Packagist and npm are not intended for registering such custom packages.

To serve private php packages  you can set up your own private packagist with Satis. A while ago my colleague Sebastian set up the Satis equivalent for the npm world. It's called Sinopia and it's easy to install. Our installation is running at npm.spatie.be.  Using this we can now pull in our custom javascript packages.

Interested using Sinopia yourself? Here's a good tutorial to get started.