Overview

The Loom-js library contains everything you need to build web apps and NodeJS services that interact with your smart contracts running on Loom.

You can install loom-js by running the following command:

yarn add loom-js
# or if you prefer...
npm install loom-js

Sample Code

In this tutorial, we're reproducing a few snippets from the Truffle DAppChain Example repository. Make sure to check out the full source code once you finish this tutorial.

Initializing the Application

To interact with the smart contract deployed to Loom, we define a class called Contract. Let's look at what's inside.

First, we create a client that will help our application "talk" to Loom:

_createClient() {
  this.privateKey = CryptoUtils.generatePrivateKey()
  this.publicKey = CryptoUtils.publicKeyFromPrivateKey(this.privateKey)
  let writeUrl = 'ws://127.0.0.1:46658/websocket'
  let readUrl = 'ws://127.0.0.1:46658/queryws'
  let networkId = 'default'
  if (process.env.NETWORK == 'extdev') {
    writeUrl = 'ws://extdev-plasma-us1.dappchains.com:80/websocket'
    readUrl = 'ws://extdev-plasma-us1.dappchains.com:80/queryws'
    networkId = 'extdev-plasma-us1'
  }

  this.client = new Client(networkId, writeUrl, readUrl)

  this.client.on('error', msg => {
    console.error('Error on connect to client', msg)
    console.warn('Please verify if loom command is running')
  })
}

Next, we want to retrieve the user's address:

_createCurrentUserAddress() {
  this.currentUserAddress = LocalAddress.fromPublicKey(this.publicKey).toString()
}

And instantiate LoomProvider:

_createWebInstance() {
  this.web3 = new Web3(new LoomProvider(this.client, this.privateKey))
}

At this point, we are ready to create an instance of the smart contract and start listening to events:

async _createContractInstance() {
  const networkId = await this._getCurrentNetwork()
  this.currentNetwork = SimpleStore.networks[networkId]
  if (!this.currentNetwork) {
    throw Error('Contract not deployed on DAppChain')
  }

  const ABI = SimpleStore.abi
  this.simpleStoreInstance = new this.web3.eth.Contract(ABI, this.currentNetwork.address, {
    from: this.currentUserAddress
  })

  this.simpleStoreInstance.events.NewValueSet({ filter: { _value: 10 }}, (err, event) => {
    if (err) console.error('Error on event', err)
    else {
      if (this.onEvent) {
        this.onEvent(event.returnValues)
      }
    }
  })

  this.simpleStoreInstance.events.NewValueSetAgain({ filter: { _value: 47 }}, (err, event) => {
    if (err) console.error('Error on event', err)
    else {
      setTimeout(() => alert("Loooomy help me :)"))
      if (this.onEvent) {
        this.onEvent(event.returnValues)
      }
    }
  })
}

addEventListener(fn) {
  this.onEvent = fn
}

Writing data to Loom

Here's how you can write data to Loom and mutate the state of your smart contract:

async setValue(value) {
  // Just a small test with Loomy
  if (value == 47) {
    return await this.simpleStoreInstance.methods.setAgain(value).send({
      from: this.currentUserAddress
    })
  }

  return await this.simpleStoreInstance.methods.set(value).send({
    from: this.currentUserAddress
  })
}

Reading data from Loom

Reading data from Loom is as simple as:

async getValue() {
  return await this.simpleStoreInstance.methods.get().call({
    from: this.currentUserAddress
  })
}

Web3, LoomProvider and Truffle