// This function gets called when the end-user clicks on some date.
function selected(cal, date) {
  cal.sel.value = date; // just update the date in the input field.
  //if (cal.sel.id == "sel1" || cal.sel.id == "sel3")
    // if we add this call we close the calendar on single-click.
    // just to exemplify both cases, we are using this only for the 1st
    // and the 3rd field, while 2nd and 4th will still require double-click.
    cal.callCloseHandler();
}

// And this gets called when the end-user clicks on the _selected_ date,
// or clicks on the "Close" button.  It just hides the calendar without
// destroying it.
function closeHandler(cal) {
  cal.hide();                        // hide the calendar
}
function showCalendar(id) {
  var format = 'y-mm-dd';
  var el = document.getElementById(id);
  if (calendar != null) {
    // we already have some calendar created
    calendar.hide();                 // so we hide it first.
  } else {
    // first-time call, create the calendar.
    var cal = new Calendar(false, null, selected, closeHandler);
    // uncomment the following line to hide the week numbers
    // cal.weekNumbers = false;
    calendar = cal;                  // remember it in the global var
    cal.setRange(1900, 2070);        // min/max year allowed.
    cal.create();
  }
  calendar.setDateFormat(format);    // set the specified date format
  calendar.parseDate(el.value);      // try to parse the text in field
  calendar.sel = el;                 // inform it what input field we use
  calendar.showAtElement(el);        // show the calendar below it

  return false;
}