Step 1: Set up a Blockchain class
javascript

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.calculateHash();
}

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

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

createGenesisBlock() {
return new Block(0, “01/01/2025”, “Genesis Block”, “0”);
}

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

addBlock(newBlock) {
newBlock.previousHash = 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 previousBlock = this.chain[i – 1];

if (currentBlock.hash !== currentBlock.calculateHash()) return false;
if (currentBlock.previousHash !== previousBlock.hash) return false;
}
return true;
}
}