FullStack AES-GCM Encryption Decryption using NodeJS and Browser standard libraries (native crypto API)

encrypt.js

//----------------------------------------------------------------
// ------------------- ServerSide(NODE.JS) -------------------
//----------------------------------------------------------------
function encrypt(message){
  const KEY = crypto.randomBytes(32)
  const IV = crypto.randomBytes(16)
  const ALGORITHM = 'aes-256-gcm';
  
  const cipher = crypto.createCipheriv(ALGORITHM, KEY, IV);
  let encrypted = cipher.update(message, 'utf8', 'hex');
  encrypted += cipher.final('hex');
  const tag = cipher.getAuthTag()
  
  let output = {
    encrypted,
    KEY: KEY.toString('hex'),
    IV: IV.toString('hex'),
    TAG: tag.toString('hex'),
  }
  return output;
}


//------------------------------------------------------------------
// ------------------- ClientSide -------------------
//------------------------------------------------------------------
function decrypt() {
  let KEY = hexStringToArrayBuffer(data.KEY);
  let IV = hexStringToArrayBuffer(data.IV);
  let encrypted = hexStringToArrayBuffer(data.encrypted + data.TAG);

  window.crypto.subtle.importKey('raw', KEY, 'AES-GCM', true, ['decrypt']).then((importedKey)=>{
    console.log('importedKey: ', importedKey);
    window.crypto.subtle.decrypt(
      {
        name: "AES-GCM",
        iv: IV,
      },
      importedKey,
      encrypted
    ).then((decodedBuffer)=>{
      let plaintext = new TextDecoder('utf8').decode(decodedBuffer);
      console.log('plainText: ', plaintext);
    })
 })
  
function hexStringToArrayBuffer(hexString) {
  hexString = hexString.replace(/^0x/, '');
  if (hexString.length % 2 != 0) {
    console.log('WARNING: expecting an even number of characters in the hexString');
  }
  var bad = hexString.match(/[G-Z\s]/i);
  if (bad) {
      console.log('WARNING: found non-hex characters', bad);    
  }
  var pairs = hexString.match(/[\dA-F]{2}/gi);
  var integers = pairs.map(function(s) {
      return parseInt(s, 16);
  });
  var array = new Uint8Array(integers);
  return array.buffer;
}