.js

var split = require('binary-split-streams2'),
    fs = require('fs');

function requestStream(url) {
  return Kefir.stream(emitter => {
     let req = bhttp.get(url, { stream: true })
      .pipe(split()); // default is \n -- no regex support, use a different module if you need variable line terminators
     req.on('data', chunk => emitter.emit(chunk));
     req.on('error', err => {
       emitter.error(err); emitter.end();
     });
     req.on('end', () => emitter.end());
  })
}

var outFile = fs.createWriteStream('./outfile.log');

Kefir.sequentially(0, listOfUrls)
  .flatMapConcurLimit(requestStream, 3) // 3 open at once max
  .onValue(chunk => outFile.write(chunk))
  .onError(err => console.error(err))
  .onEnd(() => {
    outFile.end();
    console.log('done')
  });