Recursive Promise FileReader

filereader.js

const fs = require('fs');

const flatten = arrays => [].concat.apply([], arrays);
const isFile = err => err && err.code === 'ENOTDIR';
const getChildPaths = (dir, filenames) => filenames.map(f => dir + '/' + f);

const readFiles = (reader, path) => {
  return new Promise((resolve, reject) => {
    reader.readdir(path, (err, filenames) => {
      resolve({ path, filenames, err });
    });
  })
    .then(({ path, filenames, err }) => {
      if (isFile(err)) {
        return [path];
      }

      const paths = getChildPaths(path, filenames);
      const promises = paths.map(p => readFiles(reader, p));
      return Promise.all(promises).then(flatten);
    });
};

readFiles(fs, '.').then(console.log);