node.js stream with promisified reading (vanilla)

read-stream-async.js

const fs = require('fs');
const path = require('path');

const testfile = path.join(path.resolve(), 'test.txt');
read(testfile);

async function read(filepath) {
  const rstream = fs.createReadStream(filepath, {highWaterMark: 70, encoding: 'utf-8'});

  let data;
  let reader = readStream(rstream);
  while(null !== (data = await reader())) {
    console.log('data=' + data);
  }
  console.log('done');
}

function readStream(rstream) {
  let def;

  rstream.on('error', (err) => {
    console.error(err);
    def && def.resolve(null);
  });
  rstream.on('end', () => def && def.resolve(null));
  rstream.on('data', (x) => def && def.resolve(x || ''));

  return () => {
    def = deferred();
    return def.promise;
  };
}

function deferred() {
  let resolve;
  let reject;
  const promise = new Promise((resolveFn, rejectFn) => {
    resolve = resolveFn;
    reject = rejectFn;
  });
  return {promise, resolve, reject};
}