[angra_mainyu]

This is a solved problem.

You tackle it by doing two things:

1) use a bundler (rollup or webpack) if your code is big so it can be chunked and loaded quickly

2) have a loading spinner by default

Some developers have a dogmatic zeal against loading spinners, but users are very accustomed to them.

In fact, it's possible for websites to load _too_ fast, seeming unnatural to users (who at this point in time are very much expecting the flow to be request->spinner->load).