I would not say that it answers all of your questions, but I thought it was nice. I guess the short answer for me was CommonJS and thus Browserify on the front-end.
Note: I'm not a JS expert, but at work we have a number of repos written in JS, both "back-end" Node.js projects, and "front-end" JS and a Chrome extension (also JS). I know for a fact that I don't know what I'm doing (I am not going to take the time to learn about CommonJS, AMD, UMD, "Interop", etc., and I've just learned the basics of ES5 and am not eager to rush into ES6 or Babel) and when I find myself in such cases I like to take the simplest approach that seems to work.
I would not say that it answers all of your questions, but I thought it was nice. I guess the short answer for me was CommonJS and thus Browserify on the front-end.
Note: I'm not a JS expert, but at work we have a number of repos written in JS, both "back-end" Node.js projects, and "front-end" JS and a Chrome extension (also JS). I know for a fact that I don't know what I'm doing (I am not going to take the time to learn about CommonJS, AMD, UMD, "Interop", etc., and I've just learned the basics of ES5 and am not eager to rush into ES6 or Babel) and when I find myself in such cases I like to take the simplest approach that seems to work.