Javascript date validation on onkeyUp using the leap year functionality

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

i am not sure at this point, if the error is happening on leap year or onchange issue