rq

function req() {
    var year = document.getElementById('year').value;
    var month = document.getElementById('month').value;
    var day = document.getElementById('day').value;

    function leapYear(year){
      return year % 4 == 0 && (year % 100 == 0 || year % 400 == 0);
    }

    if (month == 2 && day > 28 && !leapYear(year)){
        alert("Wrong Date!");
    }
    else if ((month == 4 || month == 6 || month == 9 || month == 11) && day > 30){
        alert("Wrong Date!");
    }
    else {

        var request = $.ajax({
            url: "main.php",
            method: "POST",
            data: {year: year, month: month, day: day},
            success: function (res) {
                //document.documentElement.innerHTML = res;
                alert(year + " " + month + " " + day);
            }
        })
    }
}