foreign-currency-diff.js

// https://www.esunbank.com.tw/bank/Layouts/esunbank/Accessibility/rate_exchange.aspx
var trs = document.querySelectorAll('table.inteTable tr')
for (var i = 0; i < trs.length; ++i) {
  var buyPrice = trs[i].querySelector('td:nth-child(2)'),
      selPrice = trs[i].querySelector('td:nth-child(3)');
  if (buyPrice == null || isNaN(buyPrice.innerText) || selPrice == null || isNaN(selPrice.innerText)) {
    continue;
  }
  console.log(1);
  var buyPriceFloat = parseFloat(buyPrice.innerText),
      selPriceFloat = parseFloat(selPrice.innerText),
      diff = Math.round((selPriceFloat - buyPriceFloat) / selPriceFloat * 10000) / 100;
  
  selPrice.innerText = selPrice.innerText + ' (' + diff + '%)';
}