JAVASCRIPT

Simple Cryptocurrency Blockchain Using JavaScript

const sha256 = require('sha256');

function Blockchain() {
    this.chain = [];   //stores our blocks
    this.pendingTransactions = []; //this contains our pending transaction before create a new block
    this.createNewBlock(100, '0', '0');
}

Blockchain.prototype.createNewBlock = function(nonce, prevBlockHash, hash){
    const newBlock = {
        index : this.chain.length + 1,
        timestamp : Date.now(),
        transactions : this.pendingTransactions,
        nonce : nonce,
        prevBlockHash : prevBlockHash,
        hash : hash
    };

    this.pendingTransactions = [];
    this.chain.push(newBlock);

    return newBlock;
}

Blockchain.prototype.getLastBlock = function() {
    return this.chain[this.chain.length - 1];
}

Blockchain.prototype.createNewTransaction = function(amount, sender, recipient) {
    const NewTransaction = {
        amount : amount,
        sender : sender,
        recipient : recipient
    };

    this.pendingTransactions.push(NewTransaction);

    return this.getLastBlock()['index'] +1;
}

Blockchain.prototype.hashBlock = function(prevBlockHash, currentBlockData, nonce) {
    const dataString  = prevBlockHash + nonce.toString() + JSON.stringify(currentBlockData);
    const hash = sha256(dataString);

    return hash;
}

Blockchain.prototype.proofOfWork = function(prevBlockHash, currentBlockData) {
    let nonce = 0;
    let hash = this.hashBlock(prevBlockHash, currentBlockData, nonce);

    while (hash.substring(0,4) !== '0000') {
        nonce++;
        hash = this.hashBlock(prevBlockHash, currentBlockData, nonce);
    }

    return nonce;
}

module.exports = Blockchain;