USD is fairly widely used. But it's not "code" in the sense that I mean it. It's (mostly) declarative (like HTML) so I lump it in with obj, fbx and gltf.
I am assuming code means "executable code" - I know the boundaries are fuzzy here and some file formats are Turing complete - but I guess what I'm saying is that I'm still not sure what you're asking!
Sorry for not being clear on the code part. I assumed USD and the like would be the norm now. "Complex objects" is not really helpful in this context, though.