Hello there,
I was looking to use some of the csg libs out there in the wild… And one of them is requiring to have UV mapping on my meshes. Is there an efficient way to create this mapping? Since I don’t need to use precises texture, there is no need for it to be perfect.
Thanks ! 
You usually need a special algorithm for this (which does not exist for three.js) or doing it manually in a content creation tool.
UV coordinates are expressed in 2D space whereas vertices are in 3D. If you have no idea about the shape of a geometry, there is no easy way to derive texture cooridnates.