Sign a transaction in JS

transactionSigner.js

const CryptoJS = require("crypto-js");
const EC = require('elliptic').ec;
const secp256k1 = new EC('secp256k1');

function signData(data, privKey) {
    let keyPair = secp256k1.keyFromPrivate(privKey);
    let signature = keyPair.sign(data);
    return [signature.r.toString(16), signature.s.toString(16)];
}

function verifySignature(data, publicKey, signature) {
    let key = secp256k1.keyFromPublic(publicKey, 'hex');
    let valid = key.verify(msg, {r: signature[0], s: signature[1]});
    return valid;
}

class Transaction {
    constructor(from,
                to,
                value,
                fee,
                dateCreated,
                senderPubKey,
                transactionDataHash,
                senderSignature,
                minedInBlockIndex,
                transferSuccessful)
    {
        this.from = from; // Sender address: 40 hex digits
        this.to = to; // Recipient address: 40 hex digits
        this.value = value; // Transfer value: integer
        this.fee = fee; // Mining fee: integer
        this.dateCreated = dateCreated;   // ISO-8601 string
        this.senderPubKey = senderPubKey; // 65 hex digits
        this.transactionDataHash = transactionDataHash; // 64 hex digits

        // Calculate the transaction data hash if it is missing
        if (this.transactionDataHash === undefined)
            this.calculateDataHash();

        this.senderSignature = senderSignature; // hex_number[2][64]
        this.minedInBlockIndex = minedInBlockIndex; // integer
        this.transferSuccessful = transferSuccessful; // bool
    }

    calculateDataHash() {
        let tranData = {
            'from': this.from,
            'to': this.to,
            'senderPubKey': this.senderPubKey,
            'value': this.value,
            'fee': this.fee,
            'dateCreated': this.dateCreated
        };
        let tranDataJSON = JSON.stringify(tranData);
        this.transactionDataHash = CryptoJS.SHA256(tranDataJSON).toString();
    }

    sign(privateKey) {
        this.senderSignature = signData(
            this.transactionDataHash, privateKey);
    }

    verifySignature() {
        return verifySignature(this.transactionDataHash,
            this.senderPubKey, this.senderSignature);
    }
};