json – How to build from source using npm

I’m trying to build a custom font, based on Iosevka, from source. https://github.com/be5invis/Iosevka

It tells me nodejs must be installed. The following command doesn’t work though.

npm run build -- contents::iosevka

I need a build script. I just initialized using npm init, so I don’t have any scripts yet. Every online source has a different way to implement the script but I haven’t found a way to get mine to work.