Javascript date validation on onkeyUp using the leap year functionality

Question

I have this piece of code where i am trying to validate the jquery based Date of Birth Validation.

is there any JS function which also checks the full date if it falls in a leap year or not, i am trying this but it does seems to be working

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]));
}

date i tested is: 02/29/1920 - it is giving false (edited)

testing it like this:

    function init_inputOnKeyUp(){
        $('select[name="day"],select[name="year"]').off('change');
        $('select[name="month"],select[name="day"],select[name="year"]').on('change', function(e) {
        if (type == 'select') {
            var newdate = $('select[name="month"]').val() + '/' + $('select[name="day"]').val() + '/' + $('select[name="year"]').val();
                        var results = isValidDate(newdate.toString());
                        console.log(results);
                        console.log(newdate.toString());
        }
        });
}

problem i can't use any extra library like moment.js

the error is it is always giving me false when i try to validate with a full date

also i changed my function toL

this function should return me true, but it is returning me "undefined"

function isValidDate(sDate) {
    var dateformat = /^(0?[1-9]|[12][0-9]|3[01])[\/\-](0?[1-9]|1[012])[\/\-]\d{4}$/;
    if (sDate.match(dateformat)) {
        var seperator1 = sDate.split('/');
        var seperator2 = sDate.split('-');

        if (seperator1.length > 1) {
            var splitdate = sDate.split('/');
        } else if (seperator2.length > 1) {
            var splitdate = sDate.split('-');
        }
        var dd = parseInt(splitdate[0]);
        var mm = parseInt(splitdate[1]);
        var yy = parseInt(splitdate[2]);
        var ListofDays = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
        if (mm == 1 || mm > 2) {
            if (dd > ListofDays[mm - 1]) {
                return false;
            }
        }
        if (mm == 2) {
            var lyear = false;
            if ((!(yy % 4) && yy % 100) || !(yy % 400)) {
                lyear = true;
            }
            if ((lyear == false) && (dd >= 29)) {
                return false;
            }
            if ((lyear == true) && (dd > 29)) {
                return false;
            }
        }
    } else {
        return false;
    }
}