primitive blockchain implementation in javascript

Block.js

const sha256 = require("crypto-js/sha256");

function Block(data, parent) {
  if ( parent) {
    this.index = parent.index + 1;
    this.parentHash = parent.hash;
  } else {
    this.index = 0;
    this.parentHash = null;
  }

  this.data = data;

  this.timestamp = Date.now();
  this.hash = Block.calculateHash(this);
}

// static methods that are not called on instances of Block

// considering switching this over to node's crypto library
Block.calculateHash = block =>
  sha256(block.index + block.parentHash + block.timestamp + JSON.stringify(block.data)).toString();

Block.validate= (block, parent) =>
    parent.index + 1 === block.index &&
    parent.hash === block.parentHash &&
    Block.calculateHash(block) === block.hash;

module.exports = Block;

Blockchain.js

const Block = require('./Block.js');

function Blockchain(chain) {
  if (chain) {
    if (!Blockchain.validateChain(chain)) {
      throw new Error('Invalid chain.');
    }
    this.chain = chain;
  } else {
    this.chain = [new Block('genesis block')];
  }
}

Blockchain.prototype.getData = function () {
  return this.chain.map(block => block.data);
};

Blockchain.prototype.getChain = function () {
  return this.chain;
};

Blockchain.prototype.getGenesisBlock = function () {
  return this.chain[0];
};

Blockchain.prototype.getLatestBlock = function () {
  return this.chain[this.chain.length - 1];
};

Blockchain.prototype.add = function (data) {
  const parent = this.getLatestBlock();
  const block = new Block(data, parent);
  this.chain.push(block);
  return block;
};

Blockchain.prototype.update = function (chain) {
  const isValid = Blockchain.validateChain(chain, this.getGenesisBlock());
  const isChainLonger = chain.length > this.chain.length;

  if (isValid && isChainLonger) {
    this.chain = chain;
    return true;
  }
  return false;
};

Blockchain.prototype.toJSON = function () {
  return JSON.stringify(this.chain);
};

// static method that is not called on instances of Block
Blockchain.validateChain = function (chain, genesis) {
  const isGenesisInvalid =
    genesis && Block.calculateHash(genesis) !== chain[0].hash;

  if (!Array.isArray(chain) || chain.length === 0 || isGenesisInvalid) {
    return false;
  }

  return chain.reduce(
    (valid, block) =>
      (block.index !== 0 && Block.validate(block, chain[block.index - 1])) ||
      valid,
    true
  );
};

module.exports = Blockchain;

example.js

const Blockchain = require('./Blockchain.js');

const b = new Blockchain();

b.add({
  from: 'fielding',
  to: 'jeffrey',
  amount: 15,
});

b.add({
  from: 'jeffrey',
  to: 'chad',
  amount: 10,
});

b.add({
  from: 'chad',
  to: 'fielding',
  amount: 5,
});


console.log('full chain: \r\n', b.getChain(), '\r\n\r\n');

console.log('data only: \r\n', b.getData(), '\r\n\r\n');

console.log('genesis block: \r\n', b.getGenesisBlock(), '\r\n\r\n');

console.log('latest block: \r\n', b.getLatestBlock(), '\r\n\r\n');