Class Transaction

src/blockchain.js:7–73

const debug = require('debug')('savjeecoin:blockchain');

class Transaction {
  /**
   * @param {string} fromAddress
   * @param {string} toAddress
   * @param {number} amount
   */
  constructor(fromAddress, toAddress, amount) {
    this.fromAddress = fromAddress;
    this.toAddress = toAddress;
    this.amount = amount;
    this.timestamp = Date.now();
  }

  /**
   * Creates a SHA256 hash of the transaction
   *
   * @returns {string}
   */
  calculateHash() {
    return crypto
      .createHash('sha256')
      .update(this.fromAddress + this.toAddress + this.amount + this.timestamp)
      .digest('hex');
  }

  /**
   * Signs a transaction with the given signingKey (which is an Elliptic keypair
   * object that contains a private key). The signature is then stored inside the
   * transaction object and later stored on the blockchain.
   *
   * @param {string} signingKey
   */
  sign(signingKey) {
    // You can only send a transaction from the wallet that is linked to your
    // key. So here we check if the fromAddress matches your publicKey
    if (signingKey.getPublic('hex') !== this.fromAddress) {
      throw new Error('You cannot sign transactions for other wallets!');
    }

    // Calculate the hash of this transaction, sign it with the key
    // and store it inside the transaction object
    const hashTx = this.calculateHash();
    const sig = signingKey.sign(hashTx, 'base64');

    this.signature = sig.toDER('hex');
  }

  /**
   * Checks if the signature is valid (transaction has not been tampered with).
   * It uses the fromAddress as the public key.
   *
   * @returns {boolean}
   */
  isValid() {
    // If the transaction doesn't have a from address we assume it's a
    // mining reward and that it's valid. You could verify this in a
    // different way (special field for instance)
    if (this.fromAddress === null) return true;