Google Spreasheet Script

function getCurrencyRates() {
  const updateTime = 12000;
  const exchangeUrl = 'https://api.privatbank.ua/p24api/pubinfo?exchange&json&coursid=11';
  const cache = CacheService.getScriptCache();

  if ((rates = cache.get('rates')) == null){
    rates = UrlFetchApp.fetch(exchangeUrl).getContentText();
    cache.put('rates', rates, 600);
  }

  Logger.log(typeof JSON.parse(rates));
  return JSON.parse(rates)[0];
}

function convertUahToUsd(uah) {
  if (!uah) { return Logger.log('Nothing has been passed as an argument to convert'); }

  const rates = getCurrencyRates();
  return Math.ceil(uah /rates.sale);
}

function convertUsdToUah(usd) {
  if (!usd) { return Logger.log('Nothing has been passed as an argument to convert'); }

  const rates = getCurrencyRates();
  return Math.floor(rates.buy * usd);
}

/** Triggers **/
function onOpen() {
  getCurrencyRates();
}

function testConvertUahToUsd() {
  getCurrencyRates();
  convertUahToUsd(1000);
}

function testConvertUsdToUah() {
  getCurrencyRates();
  convertUsdToUah(900);
}