function isdate(cvalue)
  {
  var re = /^\d{2}\/\d{2}\/\d{4}$/;
  var str2 = cvalue.replace(/(^\s*)|(\s*$)/,"");
  if (str2.length < 1) return   true;

  if (re.test(cvalue))
  {
    var day = cvalue.substr(0, 2);
    var month = cvalue.substr(3, 2);
    var year = cvalue.substr(6, 4);
    var days_per_month = new Array(31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31);

    day = day.replace(/^0+/, ""); month = month.replace(/^0+/, "");
    if (islyear(year)) days_per_month[1] = 29;

    if ((month > 0) && (month <= 12) && (day > 0) && (day <= days_per_month[month-1])) return true;
  }
   return false;
  }

// Функция проверки високосного года
  function islyear(year)
  {
    if (!(year % 100)) year = year / 100;
    return !(year % 4);
  }