USD srednji_tecaj in Google Sheets via HNB API V3

usdTecajNaDan.gs

// Custom Functions in Google Sheets:
// https://developers.google.com/apps-script/guides/sheets/functions
// 
function usdTecajNaDan(value) {
  function formatDatum(value) {
    switch (typeof value) {
      case "string":
        return value;
      case "object":
        // assuming it's a date object
        let date = new Date(value);
        // return only date part (without time)
        return date.toISOString().substring(0, 10);
      default:
        throw Error(`invalid value type: ${typeof value}`);
    }
  }

  const datumISO = formatDatum(value);

  // check date format which HNB API V3 expect, e.g. 2023-02-12
  if (!datumISO.match(/^\d{4}-([0]\d|1[0-2])-([0-2]\d|3[01])$/g)) {
    throw Error(`invalid ISO date format: ${datumISO}`);
  }

  const url = "https://api.hnb.hr/tecajn-eur/v3?valuta=USD&datum-primjene=" + datumISO;
  const responseText = UrlFetchApp.fetch(url).getContentText();
  // Logger.log(responseText);
  return JSON.parse(responseText)[0].srednji_tecaj;
}