NodeJS backpressure streams with prioritisation

vowels-vs-consonants.ts

const through2 = require('through2');
const split2 = require('split2');

var vowels = through2({ objectMode: true });
var consonants = through2({ objectMode: true });
var muxed = through2({ objectMode: true, highWaterMark: 1 });

[vowels, consonants].forEach(x => x.pipe(muxed));

muxed.pipe(process.stderr);

function demux(chunk, encoding, callback) {
  if (/^[aeiuo]/.test(chunk)) {
    vowels.push(chunk);
    vowels.resume();
  } else {
    consonants.push(chunk);
  }
  callback();
}

const x = process.stdin
  .pipe(split2(y => y))
  .pipe(through2({ objectMode: true }, demux));

// for x in a i b c d e i f g h i j k l; do echo "$x"; done | node ....