encrypt.js

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

const AppendInitVect = require('./appendInitVect');
const getCipherKey = require('./getCipherKey');

function encrypt({ file, password }) {
  // Generate a secure, pseudo random initialization vector.
  const initVect = crypto.randomBytes(16);
  
  // Generate a cipher key from the password.
  const CIPHER_KEY = getCipherKey(password);
  const readStream = fs.createReadStream(file);
  const gzip = zlib.createGzip();
  const cipher = crypto.createCipheriv('aes256', CIPHER_KEY, initVect);
  const appendInitVect = new AppendInitVect(initVect);
  // Create a write stream with a different file extension.
  const writeStream = fs.createWriteStream(path.join(file + ".enc"));
  
  readStream
    .pipe(gzip)
    .pipe(cipher)
    .pipe(appendInitVect)
    .pipe(writeStream);
}

This should be what you're looking for: https://stackoverflow.com/a/25650163

Good luck!