jQuery Check if Date is Valid

function isValidDate(s) {
  var bits = s.split('/');
  var d = new Date(bits[2] + '/' + bits[1] + '/' + bits[0]);
  return !!(d && (d.getMonth() + 1) == bits[1] && d.getDate() == Number(bits[0]));
}

//Test it!
var currentDate = new Date('31/09/2011');
console.log(isValidDate(currentDate.toString()));
console.log(isValidDate('30/09/2011'));

function daysInMonth(month, year) {
    return new Date(year, month, 0).getDate();
}

//Test it!
daysInMonth('09','2011');
//Output: 30

/* check a date is valid, if not revert to last day in month */
validateDateLastDayMonth: function()
{
    /* helpers */
    function isValidDate(s) {
      var bits = s.split('/');
      var d = new Date(bits[2] + '/' + bits[1] + '/' + bits[0]);
      return !!(d && (d.getMonth() + 1) == bits[1] && d.getDate() == Number(bits[0]));
    }

    function daysInMonth(month, year) {
        return new Date(year, month, 0).getDate();
    }
   
    /* init */
    var currentDate = new Date(),
    currentMonth = currentDate.getMonth() + 1,
    lastDayOfMonth = new Date(currentDate.getFullYear(), (currentDate.getMonth() - 1), 0).getDate(),
    departureDate = FCL.DATETIME.futureDateDays(14),
    depDate = departureDate.split('/'),
    departureDateMonth = depDate[1];
    if (departureDateMonth != currentMonth) {
        departureDate = FCL.DATETIME.leadingZero(lastDayOfMonth) +'/'+ FCL.DATETIME.leadingZero(currentMonth) +'/'+ depDate[2];
    }
   
    /* validate date */
    if (!isValidDate(departureDate.toString()))
    {
        var bits = departureDate.split('/');
        departureDate = FCL.DATETIME.leadingZero(daysInMonth(bits[1],bits[2])) +'/'+ FCL.DATETIME.leadingZero(currentMonth) +'/'+ depDate[2];
    }
   
    $('input[name="depDate"]').val(departureDate);
}