JavaScript in Blockchain

VilniusJs, May 2018

Jaro Šatkevič - @chompomonim


  • What is Blockchain?
  • Which blockchains actually works.
  • Intro into Bitcoin and Ethereum.
  • Ideas where JavaScript is good choice.
  • Short libraries examples.
  • What's dApps and where everything is going?

What is blockchain?


Programable money

Which of them actually works?

Which of them actually works?

Rest are mostly experiments or tokens

  • EOS - ERC20 token
  • Cardano - still in early beta
  • IOTA - early beta
  • Tron - ERC20 token
  • ...

Main parts of Bitcoin

Full node



Bitcoin core

Full node

Ledger of transactions


creation of blocks with tx


view balances, create & sign tx

UTXO based balance

In one minute

It knows only what it was told about



Oracle Service

Oracles everywhere

  • Full nodes
  • Mining software
  • Wallets of all kinds
  • Smart contracts
  • Oracles
  • Blockchain explorers
  • Blockchain monitoring
  • Payment processors
  • Exchanges (centralised / decentralised)
  • Lightning network
  • Side chains
  • Node infrastructure
  • IoT and payments
  • Gambling and games
  • ...

Is JavaScript good for Blockchain?

Isn't C++, Go, Rust or Java mostly used for blockchain creation?


Especially for wallets and oracles

JS in Bitcoin

JavaScript libs and tools



Let's generate address

const bitcoin = require('bitcoinjs-lib')

const hash = bitcoin.crypto.sha256(
    Buffer.from('correct horse battery staple')
const d = bigi.fromBuffer(hash)

const keyPair = new bitcoin.ECPair(d)
const address = keyPair.getAddress()

console.log(address)  //1C7zdTfnkzmr13HfA2vNm5SJYRK6nEKyq8

JS in Ethereum

JavaScript libs and tools

Smart-contracts and Oracles



contract Auction {

    address public beneficiary;
    uint256 public auction_start;
    uint256 public auction_end;

    address public highest_bidder;
    uint256 public highest_bid;

    bool public ended;

    constructor(address _beneficiary, uint256 _bidding_time) public {
        beneficiary = _beneficiary;
        auction_start = block.timestamp;
        auction_end = auction_start + _bidding_time;

    function bid() payable public {
        require(block.timestamp < auction_end);
        require(msg.value > highest_bid);

        if (highest_bid != 0) {
            send(highest_bidder, highest_bid);

        highest_bidder = msg.sender;
        highest_bid = msg.value;

    function end_auction() public {
        require(block.timestamp >= auction_end);
        ended = true;
        send(beneficiary, highest_bid);



import Web3 from 'web3'

const web3 = new Web3(Web3.givenProvider || "ws://localhost:8546")
const contractAddress = '0x49aC4508A3B125f08d98c6D1564aE88114e4199F'
const contract = new web3.eth.Contract(contractABI, contractAddress, {})

export async function bid(amount) {
    return await{value: amount})

export async function showHighestBid() {
    return await contract.methods.highest_bid().call()

Blockchain ecosystem needs you


what's dApps?

Crypto currencies are:

Programmable money

Payment channels and  cheques are future!

Let's discuss

Jaro Šatkevič - @chompomonim -

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