Such lazy loading might be difficult to retrofit into an application designed for an environment where it can load a lot from disk to RAM quickly and has never (IME) been well design in terms of such resource use.

Some lazy loading could probably be done relatively easily where OO does on-demand load libraries, but that would significantly resource apparent in-use performance if truly done live so you'd want to background load the optional parts once the immediately needed ones are done.

I'm guessing that this is a straight compile to WASM with the minimal changes needed to things that would otherwise break completely in the different environment.

Autodesk has shared some information about how they solved this when building AutoCAD Web, which is a wasm app derived from their desktop codebase.

Video: https://www.infoq.com/presentations/autocad-webassembly/