[ksr]

I use fs.writeFileSync:

  $ node -e "fs.writeFileSync(1, Buffer.from('@'.repeat(128 * 1024))); process.exit(0);" | wc -c
  131072

[3np]

It doesn't work for all streams but for the stdout/stderr case where they can be treated like file descriptors, I prefer this simpler approach over fiddling with the Streams API.

(If blocking the process on writing synchronously to stdout is indeed what you actually want...)