//module required
const SHA256 = require("crypto-js/sha256");
class CryptoBlock {
constructor(index, timestamp, data, precedingHash = " ") {
this.index = index;
this.timestamp = timestamp;
this.data = data;
this.precedingHash = precedingHash;
this.hash = this.computeHash();
this.nonce = 0;
}
computeHash() {
return SHA256(
this.index +
this.precedingHash +
this.timestamp +
JSON.stringify(this.data) +
this.nonce
).toString();
}
proofOfWork(difficulty) {
while (
this.hash.substring(0, difficulty) !== Array(difficulty + 1).join("0")
) {
this.nonce++;
this.hash = this.computeHash();
}
}
}
class CryptoBlockchain {
constructor() {
this.blockchain = [this.startGenesisBlock()];
this.difficulty = 4;
}
startGenesisBlock() {
return new CryptoBlock(0, "01/01/2020", "Initial Block in the Chain", "0");
}
obtainLatestBlock() {
return this.blockchain[this.blockchain.length - 1];
}
addNewBlock(newBlock) {
newBlock.precedingHash = this.obtainLatestBlock().hash;
//newBlock.hash = newBlock.computeHash();
newBlock.proofOfWork(this.difficulty);
this.blockchain.push(newBlock);
}
checkChainValidity() {
for (let i = 1; i < this.blockchain.length; i++) {
const currentBlock = this.blockchain
;
const precedingBlock = this.blockchain[i - 1];
if (currentBlock.hash !== currentBlock.computeHash()) {
return false;
}
if (currentBlock.precedingHash !== precedingBlock.hash) return false;
}
return true;
}
}
let smashingCoin = new CryptoBlockchain();
console.log("smashingCoin mining in progress....");
smashingCoin.addNewBlock(
new CryptoBlock(1, "01/06/2020", {
sender: "Iris Ljesnjanin",
recipient: "Cosima Mielke",
quantity: 50
})
);
smashingCoin.addNewBlock(
new CryptoBlock(2, "01/07/2020", {
sender: "Vitaly Friedman",
recipient: "Ricardo Gimenes",
quantity: 100
})
);
console.log(JSON.stringify(smashingCoin, null, 4));
learn here for detail
https://www.smashingmagazine.com/2020/02/cryptocurrency-blockchain-node-js/ 
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