Blockchain Demo

main.js

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

class Block {
	
	constructor(index, timestamp, data, prevHash = '') {
		this.index = index;
		this.timestamp = timestamp;
		this.data = data;
		this.prevHash = prevHash;
		this.hash = this.calculateHash();
	}
	
	calculateHash() {
		return SHA256(this.index + this.prevHash + this.timestamp + JSON.stringify(this.data)).toString();
	}
	
}

class Blockchain {
	constructor() {
		this.chain = [this.createGenesisBlock()];
	}
	
	createGenesisBlock() {
		return new Block(0, "01/01/2021", "Genesis block", "0");
	}
	
	getLatestBlock() {
		return this.chain[this.chain.length - 1];
	}
	
	addBlock(newBlock) {
			newBlock.prevHash = this.getLatestBlock().hash;
			newBlock.hash = newBlock.calculateHash();
			this.chain.push(newBlock);
	}
	
	isChainValid() {
		for(let i=1; i < this.chain.length; i++) {
			const currentBlock = this.chain[i];
			const prevBlock = this.chain[i-1];
			
			if(currentBlock.hash !== currentBlock.calculateHash()) {
				return false;
			}
			
			if(currentBlock.prevHash != prevBlock.hash) {
				return false;
			}
		}
		
		return true;
	}
	
}

let tcoin = new Blockchain();
tcoin.addBlock(new Block(1, "03/09/2021", {amt: 100}));
tcoin.addBlock(new Block(1, "04/09/2021", {amt: 200}));

console.log(tcoin.isChainValid());
console.log(JSON.stringify(tcoin, null, 4));

//tempering data
tcoin.chain[2].amt = 2000;
console.log(JSON.stringify(tcoin, null, 4));
console.log(tcoin.isChainValid());

Proof of Work

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

class Block {
	
	constructor(index, timestamp, data, prevHash = '') {
		this.index = index;
		this.timestamp = timestamp;
		this.data = data;
		this.prevHash = prevHash;
		this.hash = this.calculateHash();
		this.nonce = 0;
	}
	
	calculateHash() {
		return SHA256(this.index + this.prevHash + this.timestamp + JSON.stringify(this.data) + this.nonce).toString();
	}
	
	mineBlock(complexity) {
		while(this.hash.substring(0, complexity) !== Array(complexity + 1).join("0")) {
			this.nonce++;
			//console.log(this.nonce);
			this.hash = this.calculateHash();
		}
		
		console.log(`Block mined: ${this.hash}`);
	}
	
}

class Blockchain {
	constructor(complexity = 0) {
		this.chain = [this.createGenesisBlock()];
		this.complexity = complexity;
	}
	
	createGenesisBlock() {
		return new Block(0, "01/01/2021", "Genesis block", "0");
	}
	
	getLatestBlock() {
		return this.chain[this.chain.length - 1];
	}
	
	addBlock(newBlock) {
			newBlock.prevHash = this.getLatestBlock().hash;
			//newBlock.hash = newBlock.calculateHash();
			newBlock.mineBlock(this.complexity);
			this.chain.push(newBlock);
	}
	
	isChainValid() {
		for(let i=1; i < this.chain.length; i++) {
			const currentBlock = this.chain[i];
			const prevBlock = this.chain[i-1];
			
			if(currentBlock.hash !== currentBlock.calculateHash()) {
				return false;
			}
			
			if(currentBlock.prevHash != prevBlock.hash) {
				return false;
			}
		}
		
		return true;
	}
	
}

let tcoin = new Blockchain(5);

console.log("Mining Block 1...");
tcoin.addBlock(new Block(1, "03/09/2021", {amt: 100}));

console.log("Mining Block 2...");
tcoin.addBlock(new Block(1, "04/09/2021", {amt: 200}));

console.log(JSON.stringify(tcoin, null, 4));