gistfile1.txt

let fs = require('fs');
let CombinedStream = require('combined-stream2');
let path = require('path');
let parseStream = require('json-parse-stream');

let getStreamedDir = (file) => {
  let combinedStream = CombinedStream.create();
  let extensions = ['.json'];
  if (fs.lstatSync(file).isDirectory()) {
  fs.readdirSync(file)
    .filter(f => (extensions.indexOf(path.extname(f)) >= 0))
    .forEach(f => {
      let fpath = path.join(file, f);          
      combinedStream.append(fs.createReadStream(fpath).pipe(parseStream()));
    });

  }

  return combinedStream;
  }
}

let s = getStreamedDir('my_folder');

// does s emit 'data' events?
s.on('data', (data) => {
  console.log('data: ', data);
});

test.js

let fs = require('fs');
let CombinedStream = require('combined-stream2');
let path = require('path');
let parseStream = require('json-parse-stream');

let getStreamedDir = (file, extensions) => {
  let combinedStream = CombinedStream.create();
  if (fs.lstatSync(file).isDirectory()) {
  fs.readdirSync(file)
    .filter(f => (extensions.length == 0) || (extensions.indexOf(path.extname(f)) >= 0))
    .forEach(f => {
      let fpath = path.join(file, f);          
      combinedStream.append(fs.createReadStream(fpath));
    });

  }

  return combinedStream;
  }
}

let = getStreamedDir('my_folder', ['.json']).pipe(parseStream());

/*
... the following error happens only when I do .pipe(parseStream());

Unhandled rejection TypeError: Cannot read property 'mode' of undefined
    at Stream.write (file:///home/vic/project.js:125137:33)
    at Stream.stream.write (file:///home/vic/project.js:125535:11)
    at Stream.ondata (stream.js:31:26)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at drain (file:///home/vic/project.js:125545:16)
    at Stream.stream.queue.stream.push (file:///home/vic/project.js:125551:5)
    at emit (file:///home/vic/project.js:125486:12)
    at Array.t_base (file:///home/vic/project.js:125303:24)
    at Stream.write (file:///home/vic/project.js:125286:18)
    at Stream.stream.write (file:///home/vic/project.js:125535:11)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at Stream.stream.write (file:///home/vic/project.js:124694:12)
    at CombinedStream.ondata (_stream_readable.js:555:20)
    at emitOne (events.js:96:13)
    at CombinedStream.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:176:18)
    at CombinedStream.Readable.push (_stream_readable.js:134:10)
    at file:///home/vic/project.js:110764:17
    at tryCatcher (file:///home/vic/project.js:4053:23)
Unhandled rejection TypeError: Cannot read property 'mode' of undefined
    at Stream.write (file:///home/vic/project.js:125137:33)
    at Stream.stream.write (file:///home/vic/project.js:125535:11)
    at Stream.ondata (stream.js:31:26)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at drain (file:///home/vic/project.js:125545:16)
    at Stream.stream.queue.stream.push (file:///home/vic/project.js:125551:5)
    at emit (file:///home/vic/project.js:125486:12)
    at Array.t_base (file:///home/vic/project.js:125303:24)
    at Stream.write (file:///home/vic/project.js:125286:18)
    at Stream.stream.write (file:///home/vic/project.js:125535:11)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at Stream.stream.write (file:///home/vic/project.js:124694:12)
    at CombinedStream.ondata (_stream_readable.js:555:20)
    at emitOne (events.js:96:13)
    at CombinedStream.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:176:18)
    at CombinedStream.Readable.push (_stream_readable.js:134:10)
    at file:///home/vic/project.js:110764:17
    at tryCatcher (file:///home/vic/project.js:4053:23)
 */