Check DateFormat dd/MM/yyyy using JavaScript

<script>
        function checkvaliddateformat() {
            var dateofbirth = document.getElementById("txtDateOfBirth");
            var dob = dateofbirth.value.split('/');
            var dd = dob[0];
            var mm = dob[1];
            var yy = dob[2];

            if (dd == '' || mm == '' || yy == '' || isNaN(dd) || isNaN(mm) || isNaN(yy) || dd == 0 || mm == 0 || yy == 0) {
                alert("Invalid Date of Birth");
                return false;
            }
            else {
                if (dob.length != 3) {
                    alert("Please enter Date Of Birth in (dd/mm/yyyy) format");
                    return false;
                }
                else {
                    if ((mm == 4 || mm == 6 || mm == 9 || mm == 11) && dd > 30) {
                        alert("Please enter Day less than equal to 30");
                        return false;
                    }
                    if ((mm == 1 || mm == 3 || mm == 5 || mm == 7 || mm == 8 || mm == 10 || mm == 12) && dd > 31) {
                        alert("Please enter Day less than equal to 31");
                        return false;
                    }
                    if (mm == 2) {
                        var lyear = false;
                        if ((!(yy % 4) && yy % 100) || !(yy % 400)) {
                            lyear = true;
                        }
                        if ((lyear == false) && (dd >= 29)) {
                            alert('Invalid date format in February!');
                            return false;
                        }
                        if ((lyear == true) && (dd > 29)) {
                            alert('Invalid date format in February!');
                            return false;
                        }
                    }
                    if (parseFloat(dob[1]) > 12) {
                        alert("Please enter Month less than equal to 12");
                        return false;
                    }
                    if (dob[2].length != 4) {
                        alert("Please enter Year in Four Digit (yyyy)");
                        return false;
                    }
                }
            }
        }
    </script>