Events

When a transaction is mined, smart contracts can emit events and write logs to the blockchain that the frontend can then process. Click here for more information about events.

In the following example we will show you how to find events that are emitted by Money On Chain smart contract in RSK Testnet blockchain with truffle.

Code example

const Web3 = require('web3');
//You must compile the smart contracts or use the official ABIs of the repository
const MocExchange = require('../../build/contracts/MoCExchange.json');
const truffleConfig = require('../../truffle');

/**
 * Get a provider from truffle.js file
 * @param {String} network
 */
const getDefaultProvider = network =>
  truffleConfig.networks[network].provider || truffleConfig.networks[network].endpoint;

/**
 * Get a new web3 instance from truffle.js file
 */
const getWeb3 = network => {
  const provider = getDefaultProvider(network);
  return new Web3(provider, null, {
    transactionConfirmationBlocks: 1
  });
};

const web3 = getWeb3('rskTestnet');

//Contract address on testnet
const mocExchangeAddress = '<contract-address>';

const execute = async () => {
  web3.eth.defaultGas = 2000000;

  /**
   * Loads an specified contract
   * @param {ContractABI} abi
   * @param {String} contractAddress
   */
  const getContract = async (abi, contractAddress) => new web3.eth.Contract(abi, contractAddress);

  // Loading MoCExchange contract to get the events emitted by this
  const mocExchange = await getContract(MocExchange.abi, mocExchangeAddress);
  if (!mocExchange) {
    throw Error('Can not find MoCExchange contract.');
  }

  // In this example we are getting BPro Mint events from MoCExchange contract
  // in the interval of blocks passed by parameter
  const getEvents = () =>
    Promise.resolve(mocExchange.getPastEvents('RiskProMint', { fromBlock: 1000, toBlock: 1010 }))
      .then(events => console.log(events))
      .catch(err => console.log('Error getting past events ', err));

  await getEvents();
};

execute()
  .then(() => console.log('Completed'))
  .catch(err => {
    console.log('Error', err);
  });

See getPastEvents for parameters and event structure details.