NodeJS & Browser Quick Start

Overview

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

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

yarn add zeknd-js
# or if you prefer...
npm install zeknd-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 zeknd, 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 zeknd:

_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 zeknd command is running')
  })
}

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

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

And instantiate zeknProvider:

_createWebInstance() {
  this.web3 = new Web3(new zekndProvider(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 zeknd

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

async setValue(value) {
  // Just a small test with zeknd
  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 zeknd

Reading data from zeknd is as simple as:

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