자바스크립트 날짜 유효성 체크

function isValidDate(dateStr) {

   var year = Number(dateStr.substr(0,4));
   var month = Number(dateStr.substr(4,2));
   var day = Number(dateStr.substr(6,2));

   if (month < 1 || month > 12) { // check month range
    alert("Month must be between 1 and 12.       ");
    return false;
   }

   if (day < 1 || day > 31) {
    alert("Day must be between 1 and 31.       ");
    return false;
   }

   if ((month==4 || month==6 || month==9 || month==11) && day==31) {
    alert("Month "+month+" doesn't have 31 days!       ");
    return false
   }

   if (month == 2) { // check for february 29th
    var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
    if (day>29 || (day==29 && !isleap)) {
     alert("February " + year + " doesn't have " + day + " days!       ");
     return false;
    }
   }

   return true;
  }
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