Split an app when developing but combine on the server side

Hey guys,
does maybe somebody have an idea of how to split an app into multiple parts / modules and combine them again into one app on the server side?
I am developing a Vue.js WordPress theme and want to add support for various plugins (e.g. Mailchimp, WooCommerce, etc) as an additional feature. But it seems to me impossible to add parts of the app after compiling them. Actually I can’t even compile the parts of the app without them being integrated in the app while developing . So it seems to me as I have to maintain for each feature a separated app even around 95% of the app is identical :frowning: