const promisify = (inner) =>
  new Promise((resolve, reject) =>
    inner((err, res) => {
      if (err) { reject(err) }
      resolve(res);
    })
  );

const getBalance = (account, at) =>
  promisify(cb => web3.eth.getBalance(account, at, cb));

// use getBalance
const bigNumberBalance = await getBalance('0xabcdef');
console.log(bigNumberBalance.toString());

const getTransaction = (hash) =>
  promisify(cb => web3.eth.getTransaction(hash, cb));

// use getTransaction
const transaction = await getTransaction('0xcaff');