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A simple blockchain implemented with JavaScript
const SHA256 = require("crypto-js/sha256");
class Block {
constructor(index, timestamp, data, previousHash = '') {
this.index = index;
this.previousHash = previousHash;
this.timestamp = timestamp;
this.data = data;
this.hash = this.calculateHash();
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();
}
}
}
class Blockchain{
constructor() {
this.chain = [this.createGenesisBlock()];
this.difficulty = 5;
}
createGenesisBlock() {
return new Block(0, "05/01/2018", "Genesis Block", "0");
}
getLastBlock() {
return this.chain[this.chain.length - 1];
}
addBlock(newBlock) {
newBlock.previousHash = this.getLastBlock().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 (currentBlock.previousHash !== previousBlock.hash) {
return false;
}
}
return true;
}
}
let FancyCoin = new Blockchain();
console.log('Mining block 1...');
FancyCoin.addBlock(new Block(1, "06/01/2018", {amount: 10}));
console.log('Mining block 2...');
FancyCoin.addBlock(new Block(2, "06/01/2018", {amount: 20}));
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