get-all-files.js

const path = require('path')

const getAllFiles = (dir, ext = '.js') => {
  return readDir(dir).then(children => {
    return children
      .filter(fileName => {
        const fileExtension = path.extname(fileName);
        return fileExtension.includes(ext);
      })
      .map(fileName => path.resolve(dir, fileName));
  });
};