Google AppScript RSVP

Code.gs

function getDate() {
  return new Date(new Date().toLocaleString('en', {timeZone: 'Asia/Kuala_Lumpur'}))
}

function formatTelephone(telephone) {
    if (telephone.startsWith("+6")) {
      return telephone.substring(1);
    } else if (telephone.startsWith("0")) { 
      return "6" + telephone;
    } else if (telephone.startsWith("5")) { // +65 singapore
      return "6" + telephone;
    }
    return telephone;
}

function findRowByTelephone(sheet, telephone) {
    var telephoneColumn = 2;
    var lastRow = sheet.getLastRow();

    for (var i = 2; i <= lastRow; i++) {
        var phoneValue = sheet.getRange(i, telephoneColumn).getValue();
        if (phoneValue == telephone) { // loose equality because we're comparing type number and string
            return i;
        }
    }
    return null;
}


function updateSheet(sheet, data) {
  try {
    var formattedTelephone = formatTelephone(data.telephone);
    var foundRow = findRowByTelephone(sheet, formattedTelephone);
    var timeNow = getDate(); // for timezone consistency

    if (foundRow !== null) {
        sheet.getRange(foundRow, 1, 1, 7).setValues([
            [data.fullname, formattedTelephone, data.attendance, data.paxAdult, data.paxChild, sheet.getRange(foundRow, 6).getValue(), timeNow]
        ]);
        return "updated";
    } 
    
    sheet.appendRow([
        data.fullname, formattedTelephone, data.attendance, data.paxAdult, data.paxChild, timeNow, timeNow
    ]);
    return "created";
    
  } catch (error) {
      return "failed";
  }
}

function doPost(e) {
  var result = '';

  try {
    result = updateSheet(SpreadsheetApp.getActiveSpreadsheet().getActiveSheet(), JSON.parse(e.postData.contents));
  } catch (error) {
    result = "critical";
  }

  return ContentService.createTextOutput(
      JSON.stringify({ "result": result })
  ).setMimeType(ContentService.MimeType.JSON);
}