"Loaded" part is no longer true in major JS implementations (for example, [1]).

[1] https://v8.dev/blog/preparser

That’s a broader claim than that page supports. They describe how they avoiding fully generating the internal representation and JITing it, but clearly even unused code is taking up memory and CPU time so you’d want to review your app’s usage to make sure that it’s acceptable levels of work even on low-end devices and also that your coding style doesn’t defeat some of those optimizations.