Bitcoin Computer

BitcoinComputer is a Javascript library for running smart contracts on Bitcoin.

Examples

We give a few examples of smart contracts. See bitcoincomputer.io for more documentation.

Non-Fungible Token

A non-fungible token is a Javascript class with some state. It has a constructor to initialize the state, a function to update the state, and a function to send the token to another user. The _owners controlls who may update the object. For more information see the docs.

class Token {
  constructor(state) {
    this.state = state
  }

  setState(state) {
    this.state = state
  }

  send(to) {
    this._owners = [to]
  }
}

You can deploy a token and send it to another user by running the following code.

  // create Bitcoin Computer wallet
  const computer = new Computer({
    seed: 'replace this seed', // your BIP39 seed
    chain: 'BSV' // BSV or BCH
  })

  // deploy the smart contract
  const token = await computer.new(Token, ['some state'])

  // send token to another user
  const publicKey = '03223d...46d06c8dfe'
  await token.send(publicKey)

Fungible Token

A fungible token consists of several instances of the Coin class. A coin object can hold a number of tokens. A coin can be split into two coins using the send function and the smart contract guarantees that no new tokens are created.

class Coin {
  constructor(supply, to) {
    this.tokens = supply
    this._owners = [to]
  }

  send(amount, to) {
    if(this.tokens < amount) throw new Error('insufficient funds')
    this.tokens -= amount
    return new Coin(amount, to)
  }
}

Beyond Tokens

While Bitcoin Computer can create many variants of custom tokens, it can do much more than that. It's a tool to make web application development easy. Below we show how a chat can be built on the Bitcoin Computer. The smart contract persists the objects and thus no separate database is needed to build an application.

class Chat {
  constructor() {
    this.messages = []
  }

  invite(publicKey) {
    this._owners.push(publicKey)
  }

  post(messages) {
    this.messages.push(message)
  }
}

Getting Started

Run the Tests

The easiest way to get started is to run the tests. In an empty directory run

git clone git@github.com:bitcoin-computer/computer.git
cd computer
npm install
npm test

If you get an error "Insuffienct balance in <your address>" send free testnet coins to <your address> as explained in Fund Your Computer below.

Run in Node

In an empty directory run npm init -y && npm i -s bitcoin-computer. Create file index.mjs as shown below.

import { Computer } from 'bitcoin-computer'

// the smart contract
class Counter {
  constructor() { this.n = 0 }
  inc() { this.n += 1 }
}


// run the smart contract
;(async () => {
  const seed = 'replace this seed'
  const chain = 'BSV'
  const network = 'testnet'
  const computer = new Computer({ seed, chain, network })

  const counter = await computer.new(Counter, [])
  await counter.inc()
  console.log(counter)
})()

Run the code using

node --experimental-modules index.mjs

If you get an error "Insuffienct funds in <your address>" have a look at the secion Fund Your Computer below. Run the code again after funding the wallet and you will see:

Counter {
  n: 1,
  _id: '83553f27c9e4651323f1ebb...',
  _rev: '290923708ca56ea448dd67...'
}

Run in the Browser

Create file .babelrc

{
  "presets": [ "@babel/preset-env" ],
  "plugins": [ [ "@babel/transform-runtime" ] ]
}

Create file index.html

<html>
  <body>
    <div id='el'></div>
    <script src="./index.js"></script>
  </body>
</html>

Create file index.js

import { Computer } from 'bitcoin-computer'

class Counter {
  constructor() { this.n = 0 }
  inc() { this.n += 1 }
}


;(async () => {
  const seed = 'replace this seed'
  const chain = 'BSV'
  const network = 'testnet'
  const computer = new Computer({ seed, chain, network })

  const counter = await computer.new(Counter, [])
  document.getElementById("el").innerHTML = `Counter is ${counter.n}`

  await counter.inc()
  document.getElementById("el").innerHTML = `Counter is ${counter.n}`
})()

Run the following in an empty directory

npm init -y
npm i -s bitcoin-computer
npm i -g parcel-bundler
npm i -s @babel/runtime
npm i -d @babel/plugin-transform-runtime
parcel index.html

Open your browser at http://localhost:1234. See the instructions for how to configure your own seed phrase and how to fund the computer in the sections below.

Configure Your Seed Phrase

By default the bitcoin computer object uses the pass phrase "replace this seed" to initialize the wallet. If you want to use your own seed phrase, replace the string "replace this seed" with any bip39 compatible seed phrase or generate a new one here.

Fund Your Computer

If you get an error message "Insufficient balance in address <your_address>" you need to fund the wallet inside the computer object. You can get free testnet coins from a Bitcoin SV faucet or a Bitcoin Cash Faucet and send them to <your_address>.

Documentation

You can find more information in the Bitcoin Computer Docs

Getting Help

If you have any issues ask a question in the Telegram Group or create an issue on Github.

Licence

Code it licenced under Attribution-NoDerivs 3.0 Unported. You are free to: Share, copy, and redistribute the material in any medium or format for any purpose, even commercially under the following terms:

Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
NoDerivatives — If you remix, transform, or build upon the material, you may not distribute the modified material.

This is a human-readable summary of (and not a substitute for) the license.

Beta Notice

We are in beta to indicate that there are known security vulnerabilities. Our priority is to fix all security related issues. Once done we will remove the beta tag and start a bug bounty program to find all remaining bugs.

Breaking Changes

0.4.3-beta -> 0.4.4-beta: We have switched to a named export so you'll have to write import { Computer } from 'bitcoin-computer instead of import Computer from 'bitcoin-computer
x.x.x-alpha.x -> 0.3.0-beta: Smart contracts deployed in an alpha version do not work in the beta version.
0.3.0-alpha.10 -> 0.3.0-alpha.11: We changed the default wallet derivation path from the empty string to "m/44'/0'/0'/0". To use funds from a wallet created in version 0.3.0-alpha.10 or before, set the path option to the empty string when creating a computer object.

stonekase/computer