text: const createInfuraProvider = require('eth-json-rpc-infura/src/createProvider')
  const PollingBlockTracker = require('./src/polling')
  
  
  const provider = createInfuraProvider({ network: 'mainnet' })
  const blockTracker = new PollingBlockTracker({ provider })
  
  blockTracker.on('sync', ({ newBlock, oldBlock }) => {
    if (oldBlock) {
      console.log(`sync #${Number(oldBlock)} -> #${Number(newBlock)}`)
    } else {
      console.log(`first sync #${Number(newBlock)}`)
    }
  })
  