This is a Cordova plugin that can expose the in-app purchase APIs of the Apple App Store and, in the future if needed, the Google Play Store.
Although there are existing open-source Cordova plugins, they seem to have issues. While it would be possible to modify these third-party plugins to work better, the amount of code that is really needed is quite small and so it makes sense to build the simplest plugin possible. Particularly, a small and simple plugin should be more performant and more reliable than the existing third-party plugins.