It’s an understandable question! What I do in the book as part of Space-Truckers is to load the content into a variable via import then pass that to the constructor for the Cube. By doing that, WebPack knows to bring the asset into the asset bundle and make it available to your app.
As mentioned upthread any local http server will do for running and hosting files locally as well so they can be referred to by URL. Some BJS types that load via URL may require you to modify or otherwise set a base path (I’m looking at you ParticleSystemSet!) in order to get the asset to load.
HTH!