Nodejs: How to broadcast raw transaction offline?

broadcast-txs-offline.js

const Web3 = require('web3')
const Tx = require('ethereumjs-tx')

// connect to Infura node
const web3 = new Web3(new Web3.providers.HttpProvider('https://rinkeby.infura.io/v3/3ee6d9d1b4454acea9e493bb66ed8e1c'))

// the address that will send the test transaction
const addressFrom = '0xFeBC5F91863Fc1a253362ddaD46537170Fdc61e5'
const privKey = 'xxxxxxxxxxxxxxxxxxx_METAMASKxxxxxxxxxxxxxxxxxxxx'

// the destination address
const addressTo = '0xcb238c6526AB2EADb70b2454f48629Fd38C89365'

// Signs the given transaction data and sends it. Abstracts some of the details 
// of buffering and serializing the transaction for web3.
function sendSigned(txData, cb) {
  let privateKey = null;
  try {
    privateKey = new Buffer(privKey, 'hex')
  } catch(e) {
    console.log(e)
  }

  const transaction = new Tx(txData)

  transaction.sign(privateKey)
  const serializedTx = transaction.serialize().toString('hex')

  console.log('serializedTx: ', '0x' + serializedTx);
  //web3.eth.sendSignedTransaction('0x' + serializedTx, cb)
}

// get the number of transactions sent so far so we can create a fresh nonce
web3.eth.getTransactionCount(addressFrom).then(txCount => {
  // construct the transaction data
  let txData = {};
  try{
    txData = {
      nonce: web3.utils.toHex(0),
      gasLimit: web3.utils.toHex(30000),
      gasPrice: web3.utils.toHex(10e9), // 10 Gwei
      to: addressTo,
      from: addressFrom,
      value: web3.utils.toHex(web3.utils.toWei('10000000', 'wei'))
    }
  } catch(e) {
    console.log('e: ', e)
  }

  // fire away!
  sendSigned(txData, function(err, result) {
    if (err) return console.log('error', err)
    console.log('sent', result)
  })

})