handle errors when decryption

Question

i'm using aes-256-cfb algorithm to encrypt the data. encryption and decryption works fine. but if i add a invalid cipher text to decrypt function. it's return below like values.

"L1�"

in this scenario i return null from this function, i added try catch block. but it's not getting triggered.

const crypto = require('crypto');

const algorithm = 'aes-256-cfb';


function encryptText(keyStr, text) {
  const hash = crypto.createHash('sha256');
  hash.update(keyStr);
  const keyBytes = hash.digest();

  const iv = crypto.randomBytes(16);
  const cipher = crypto.createCipheriv(algorithm, keyBytes, iv);
  console.log('IV:', iv);
  let enc = [iv, cipher.update(text, 'utf8')];
  enc.push(cipher.final());
  return Buffer.concat(enc).toString('base64');
}

function decryptText(keyStr, text) {
  const hash = crypto.createHash('sha256');
  hash.update(keyStr);
  const keyBytes = hash.digest();

  const contents = Buffer.from(text, 'base64');
  const iv = contents.slice(0, 16);
  const textBytes = contents.slice(16);
  const decipher = crypto.createDecipheriv(algorithm, keyBytes, iv);
  let res = decipher.update(textBytes, '', 'utf8');
  res += decipher.final().toString();
  return res;
} 

const decrypted = decryptText(
  'top_secret',
  "BGWmMOjy+wcMtIPUtMwyoMOZFZ3"
);

console.log(decrypted)