blockchain.js

// This is blockchain implementaion
// Be careful — it doesn't work as expected actually :)
const CryptoJS = require('crypto-js')

class Block {
  constructor(index, timestamp, data, previousHash = '0') {
    this.index = index
    this.previousHash = previousHash
    this.timestamp = timestamp
    this.data = data
    this.hash = this.calculateHash()
  }

  calculateHash() {
    return CryptoJS.SHA256([
      this.index,
      this.previousHash,
      this.timestamp,
      this.data
      ].map(element => JSON.stringify(element)).join('')
    ).toString()
  }
}

class Blockchain {
  constructor() {
    this.chain = [this.createGenesisBlock()]
  }

  createGenesisBlock() {
    return new Block(0, Date.now(), 'genesis block')
  }

  getLatestBlock() {
    return this.chain[this.chain.length - 1]
  }

  addBlock(newBlock) {
    newBlock.previousHash = this.getLatestBlock().hash
    console.log('just added', newBlock)
    this.chain.push(newBlock)
  }

  isValidChain() {
    for (let i = 1; i < this.chain.length; i++) {
      const currentBlock = this.chain[i]
      const previousBlock = this.chain[i - 1]
      if (currentBlock.hash !== currentBlock.calculateHash()) {
        console.log(currentBlock)
        console.log(currentBlock.calculateHash())
        return false
      }

      if (currentBlock.previousHash !== previousBlock.hash) {
        return false
      }
    }

    return true
  }
}


const blockchain = new Blockchain()
blockchain.addBlock(new Block(1, Date.now(), { amount: 4 }))
console.log(blockchain.isValidChain()) // WTF? why false damn it?
console.log(blockchain)