<!------------------------------------------------------------------------------------------------------->
function fnChkRequired(f)
{
  var strError = "";
  for (var intLoop = 0; intLoop < f.elements.length; intLoop++)
  {
    if (null!=f.elements[intLoop].getAttribute("REQUIRED"))
    {
      if (fnIsEmpty(f.elements[intLoop].value)) strError += "  " + f.elements[intLoop].name + "\n";
    }
  }
  if ("" != strError)
  {
    alert("Required data is missing:\n" + strError);
    event.returnValue=false;
  }
  else
  {
    event.returnValue=true;
  }      
}
<!------------------------------------------------------------------------------------------------------->

<!------------------------------------------------------------------------------------------------------->
function fnFormOpenDateTime(FrmElementID)
{
// Return the current date & time (used for indicating when a form was opened).
  var vDateTime, vStrStart;
  var vobjDate = new Date();
  var vDay     = 'str0' + (vobjDate.getDate());
  var vHour    = 'str0' + (vobjDate.getHours());
  var vMinute  = 'str0' + (vobjDate.getMinutes());
  var vMonth   = 'str0' + (1 + vobjDate.getMonth());
  var vSecond  = 'str0' + (vobjDate.getSeconds());
  var vYear    = vobjDate.getYear();
  vStrStart    = vDay.length - 2;
  vDay         = vDay.substr(vStrStart,2);
  vStrStart    = vHour.length - 2;
  vHour        = vHour.substr(vStrStart,2);
  vStrStart    = vMinute.length - 2;
  vMinute      = vMinute.substr(vStrStart,2);
  vStrStart    = vMonth.length - 2;
  vMonth       = vMonth.substr(vStrStart,2);
  vStrStart    = vSecond.length - 2;
  vSecond      = vSecond.substr(vStrStart,2);
  vDateTime    = vDay + '.' + vMonth + '.' + vYear + ' ' + vHour + ':' + vMinute + ':' + vSecond;
  document.getElementById(FrmElementID).value = vDateTime;
}
<!------------------------------------------------------------------------------------------------------->

<!------------------------------------------------------------------------------------------------------->
function fnIsEmpty(str)
{
// Check if string is empty.
  for (var intLoop = 0; intLoop < str.length; intLoop++)
    if (" " != str.charAt(intLoop)) return false;
    return true;
}
<!------------------------------------------------------------------------------------------------------->

<!------------------------------------------------------------------------------------------------------->
function fnSubmitForm()
{
  document.BookingForm.submit();
}
<!------------------------------------------------------------------------------------------------------->