Ironically this is the kind of thing that ES6 modules actually solves. It's even better if your tool is internal-facing only so that you don't have to bother with the release time older browser compatibility thing.
ES6 modules are just brilliant, it's like a breath of fresh air in JavaScript development. Your browser sees exactly the same thing as you write, which is such a great simplification. And yeah, you can still bundle/minify for production...