Loom - Part 1 - Develop and deploy a smart contract

Loom Network is a Layer 2 scaling solution for Ethereum focusing on social and gaming dApps that require a very high throughput. Loom SDK enables to generate a sidechain called dAppChain using a dPoS consensus optimised for high-scalability. Loom is contributing on Plasma which is a mechanism to securely transfer a digital asset (ERC20 or ERC721) to a mainchain.

You can run your own DAppChain using the Loom software or connect to a public one (plasma-chain, social-chain or gaming-chain) running under a dPoS Ethereum blockchain to enable scalable dApps.

For this tutorial, we will create and fund a Loom account, deploy a contract on the External Dev Plasma network called extdev and interact with it from a frontend application.

Step 1 - Install Loom on your machine and fund an account

In the first, we will install Loom software on your machine to generate a keypair and fund the account with the Loom faucet.

  1. Download the executable
$ wget https://private.delegatecall.com/loom/osx/stable/loom
$ chmod +x loom
  1. Generate a key pair
$ ./loom genkey -k priv_key -a pub_key
local address: 0xc69c707D6bFDfeC42FE221a334b8DAb2A2DD4Cef
local address base64: xpxwfWv9/sQv4iGjNLjasqLdTO8=

$ ls -l | grep key
-rw-rw-r-- 1 gjeanmart gjeanmart        88 Oct 24 16:35 priv_key
-rw-rw-r-- 1 gjeanmart gjeanmart        44 Oct 24 16:35 pub_key

The keypair is created under the same folder.

  1. Go to the Loom Faucet

  2. Enter your address generated above

  3. Click on Request and wait until you see 100 faucet-karma

Step 2: Deploy a contract on the Loom extdev network

The second step consists in writing a very simple Smart Contract in Solidity and deploy it on the Loom extdev network using Truffle framework.

  1. Install Truffle on your machine
$ npm install -g truffle
  1. Initialise your Truffle project
$ truffle init
Setting up...
Unbox successful. Sweet!


  Compile:        truffle compile
  Migrate:        truffle migrate
  Test contracts: truffle test
  1. Let’s now write a simple Smart Contract that increments and store a counter

Create a file in contracts/Counter.sol and paste the following Solidity code

pragma solidity ^0.4.20;

contract Counter {
  uint counter;

  constructor() public {
    counter = 0; // Initialise the counter to 0

  function increment() public {

  function getCounter() public view returns (uint) {
    return counter;

You can verify that your code compiles correctly with the following command $ truffle compile

  1. Now, we need to create a deployment script

Create a file in migrations/2_deploy_contracts.js and paste the following code

var Counter = artifacts.require("./Counter.sol");

module.exports = function(deployer) {
  1. Finally we need to configure the connection to the Loom extdev network as well as our wallet info

Install the following JavaScript dependencies:

$ npm install truffle-hdwallet-provider loom-truffle-provider dotenv --save-dev
  1. Copy your private key from the file previously generated (priv_key)

  2. Create a .env in the Truffle project and copy the private key like this

  1. Open the file truffle.js and add the following configuration
const LoomTruffleProvider = require('loom-truffle-provider');
const HDWalletProvider = require('truffle-hdwallet-provider');

module.exports = {
  networks: {
    extdev: {
      provider: function() {
          const privateKey = process.env.PRIVATE_KEY;
          const chainId = 'extdev-plasma-us1';
          const writeUrl = 'http://extdev-plasma-us1.dappchains.com:80/rpc';
          const readUrl = 'http://extdev-plasma-us1.dappchains.com:80/query';;
          return new LoomTruffleProvider(chainId, writeUrl, readUrl, privateKey)
      network_id: 'extdev-plasma-us1'
  1. Run the deployment to the Loom extdev network
$ truffle migrate --network extdev

Using network 'extdev'.

Running migration: 1_initial_migration.js
  Deploying Migrations...
  ... 0x67143bb5194d210fcdd5a45fd2d0230662b662689417bc6aee069fc6ddab1341
  Migrations: 0x93bf3a8a616d4e097d6dfcb12ec868284b1c7624
Saving successful migration to network...
  ... 0x4d9c5b64a3bbfe2f57bcd8a069243e212fe050d3ba2f1e72898525d6651b8a04
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Deploying Counter...
  ... 0x7e790260e05487577d5922326d2646d2268456eb750a368b9bf651bfc56d6478
  Counter: 0xc6f28cf3303e7246b91d98222e3912b2b87472a0
Saving successful migration to network...
  ... 0x8491e69910d78ea4b24e37aaf444920754828eccbc0aeb67a460cccaef3c1d88
Saving artifacts...

Step 3: Interact with the contract from the web app

In the next step, we will develop a simplistic dApp using React, Web3 and Loom-js to interact with the Smart Contract previously deployed on the Loom extdev network

  1. Initialise a React project
$ npx create-react-app frontend
$ cd frontend
  1. Install the necessary dependencies

  2. web3 (1.0.0-beta.34) This is the Ethereum compatible JavaScript API which implements the Generic JSON RPC spec

  3. loom-js is a JavaScript library for building browser apps & NodeJS services that interact with Loom
$ npm install web3@1.0.0-beta.34 loom-js --save
  1. Edit frontend/package.json and add the following line under the scripts section to access the Truffle contract artifacts from the webapp
"link-contracts": "run-script-os",
"link-contracts:linux:darwin": "cd src && ln -s ../../build/contracts contracts",
"link-contracts:win32": "cd src && mklink \\D contracts ..\\..\\build\\contracts"

The full code of this file is available here: package.json

  1. Open an edit frontend/src/App.js

  2. Imports

import Web3 from 'web3'
import { Client, LocalAddress, CryptoUtils, LoomProvider } from 'loom-js'
import Counter from './contracts/Counter.json'
// Read the user private key (from browser storage or input)
let privateKey = '0kwCiGaBdTxy...OTCwKcu+5oj1O23uP1uTqqR47liWNNw=='

// Convert the private key into a public key/account address 
this.publicKey = CryptoUtils.publicKeyFromPrivateKey(CryptoUtils.B64ToUint8Array(privateKey));
this.currentUserAddress = LocalAddress.fromPublicKey(this.publicKey).toString();

// Connect to a Loom extdev network node
this.client = new Client(
this.client.on('error', msg => {
  console.error('Error on connect to client', msg)

// Instantiate a Loom Web3Provider to sign and send transaction
this.web3Provider = new LoomProvider(this.client, CryptoUtils.B64ToUint8Array(privateKey));
this.web3 = new Web3(this.web3Provider)

// Load the contract instance
this.counter = new this.web3.eth.Contract(Counter.abi, Counter.networks['extdev-plasma-us1'].address, {
  from: this.currentUserAddress
// Get the counter value
this.counter.methods.getCounter().call().then((value) => {
  return this.setState({ value, loading: false })

// Increment the counter 
increment() {
  this.setState({ loading: true })
    this.counter.methods.increment().send({ from: this.currentUserAddress }).then((r) => {
      this.counter.methods.getCounter().call().then((value) => {
        return this.setState({ value, loading: false })

The full code of this file is available here: App.js

  1. Create a link to the Truffle JSON artefacts
$ npm run link-contracts:linux:darwin
  1. Start the webserver
$ npm start
  1. Result

After copy-pasting our private key in the input field, the application is able to connect to the Loom extdev node to interact with the contract (read and increment the counter).


Key Management: There is currently no wallet (such as Metamask) with Loom network, the enduser has to handle the private key manually (browser storage) and the dAppChain provider must most likely provide a way to recover a private key.

You can generate and manipulate a private key using loom-js like this:

// Generate a private key
const privateKey = CryptoUtils.generatePrivateKey(); 

// Retrieve the public key
const publicKey = CryptoUtils.publicKeyFromPrivateKey(privateKey); 

// Convert public key to address
const address = LocalAddress.fromPublicKey(publicKey).toString(); 

karma : is a ERC20 token, sybil resistant, that can be used to prevent spam attack via a reputation-based transaction limiting system.

extdev * Network ID: extdev-plasma-us1 * Faucet: https://faucet.dappchains.com/ * Documentation: https://loomx.io/developers/docs/en/phaser-sdk-demo-websocket.html

Code: https://github.com/gjeanmart/kauri-content/tree/master/loom_tutorial_extdev_part1