index.js

const Web3 = require('web3');
const fetch = require('node-fetch');

const POLLING_INTERVAL = 5000;
const EVENTS = {
  Transfer: {}
};

const web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:7545"));

function loadContractInstance({ abiPath, address }) {
  return new Promise((resolve, reject) => {
    fetch(abiPath).then((resp) => {
      return resp.json();
    }).then(data => {
      let instance = new web3.eth.Contract(data.abi, address);
      resolve(instance);
    });
  });
}

function rebuildTokenIndex(event) {
  console.log('rebuilding');
  // Rebuild teh index here yo:
  //
}

function pollForEvent({ instance, eventName, processCb }) {

  setTimeout(() => pollForEvent(...arguments), POLLING_INTERVAL);

  // Have to poll in dev until ganache supports WebSockets transport:
  // https://github.com/trufflesuite/ganache-cli/issues/257
  instance.getPastEvents(eventName, {
    fromBlock: 0,
  }, (error, events) => {
    events.forEach(e => {
      if (!EVENTS[eventName][e.transactionHash]) {
        EVENTS[eventName][e.transactionHash] = e;
        processCb(e);
      } else {
        console.log('...duplicate event');
      }
    });
  });
}

loadContractInstance({
  abiPath: 'http://localhost:3000/abis/WorldCupPlayerToken.json',
  address: '0x9a2b051b106f0d3be0a72defcad9799b27a3f46b',
}).then((instance) => {
  pollForEvent({
    instance,
    eventName: 'Transfer',
    processCb: rebuildTokenIndex,
  });
});