The amazing thing about computer software, relative to every other human endeavour: once you've got one component right, it's right; you can treat it like a simple little node in an even more complex design, and scale it up 1,000,000x, and it'll keep working every single time.

Once you've built a C-to-JS compiler, and a Nim-to-C compiler, you've got a perfectly-functioning Nim-to-JS compiler. There's no game of telephone gradually confusing things; the fidelity is perfect no matter how deep the pipeline goes.

(This is also what's amazing about layered packet-switched networks, come to think of it. The core switch transferring data from your phone to AWS doesn't need to speak 4G or Xen SDN; it's just coupled to them, eventually, by gateways somewhere else, and it all just keeps working, one quadrillion times per second, all over the world.)