encode Rinkeby DAI sendSignedTransaction

sendSignedTransaction.js

const receiverAddress = "<Rinkeby receiver address>"
const senderAddress = "<Rinkeby sender address>";
const privKey = "<sender private key>"; // do not disclose the private key

function sendSignedTx(transactionObject, cb) {
    let transaction = new EthTx(transactionObject);
    const privateKey = new Buffer.from(privKey, "hex");
    transaction.sign(privateKey); // sign a transaction
    const serializedEthTx = transaction.serialize().toString("hex"); // serialize the transaction
    web3.eth.sendSignedTransaction(`0x${serializedEthTx}`, cb); // send signed transaction
}

web3.eth.getTransactionCount(senderAddress).then(async (transactionNonce) => {
    const transactionObject = {
        chainId: 4,
        nonce: web3.utils.toHex(transactionNonce),
        gasLimit: web3.utils.toHex(500000),
        gasPrice: web3.utils.toHex(10000000000),
        value: 0,
        to: daiExchangeAddress,
        from: senderAddress,
        data: exchangeEncodeABI
    };

    sendSignedTx(transactionObject, (err, ret) => {
        if (err) {
            console.log("An error occurred", err)
            return
        }
        console.log("The txHash is: ", ret)
    });
});