The original is a custom loader (MAIN/U2.ASM) that unpacks parts out of one archive and chain-executes them, keeping the music playing across the transitions. Each part is an ordinary DOS executable with its own main().
The port mirrors that: one host module owning the clock, the display and the phase machine, and one JavaScript module per part, each ported from that part’s own source directory. Parts hand each other the screen — several transitions are pixel-identical across the boundary by design, and the port reproduces that rather than fading between them.