Check valid date.js

function isValidDate(date) {
  var day   = date.substr(0, 2),
      month = date.substr(3, 2),
      year  = date.substr(6, 4);

  return !(
    (month < 1 || month > 12) ||
    (day < 1 || day > 31) ||
    ((month == 4 || month == 6 || month == 9 || month == 11) && day > 30) ||
    (month == 2 && day > 29) ||
    (month == 2 && day > 28 && !(year % 4 == 0 && (year % 100 == 0 || year % 400 == 0)))
  );
}