unzip3.js

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

const directoryFiles = fs.readdirSync('./data');

directoryFiles.forEach(filename => {
  const fileContents = fs.createReadStream(`./data/${filename}`);
  const writeStream = fs.createWriteStream(`./data/${filename.slice(0, -3)}`);
  const unzip = zlib.createGunzip();
  fileContents.pipe(unzip).pipe(writeStream);
});