main.js

const SHA256 = require('crypto-js/sha256')

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

	calculateHash() {
		return SHA256(this.index + this.previousHash + this.timestamp + JSON.stringify(this.data) + this.nonce).toString()
	}

	mineBlock(difficulty) {
		while(this.hash.substring(0, difficulty) !== Array(difficulty + 1).join("0")) {
			this.nonce++
			this.hash = this.calculateHash()
		}
		console.log(`Block mined ${this.hash}`)
	}
}

class Blockchain{
	constructor() {
		this.chain = [this.createGenesisBlock()]
		this.difficulty = 5
	}

	createGenesisBlock() {
		return new Block(0, "01/01/2017", "Genesis block", "0")
	}

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

	addBlock(newBlock) {
		newBlock.previousHash = this.getLatestBlock().hash
		newBlock.mineBlock(this.difficulty)
		this.chain.push(newBlock)
	}

	isChainValid() {
		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()) {
				return false
			}

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

		return true
	}
}

let sergioCoin = new Blockchain()
console.log("Minning block 1...")
sergioCoin.addBlock(new Block(1, "10/07/2017", {amount: 4}))

console.log("Minning block 2...")
sergioCoin.addBlock(new Block(2, "10/07/2017", {amount: 10}))