Validation expression using one validation

<script language ="javascript" >
    function delval() {
        var num = document.getElementById("txtdate").value;
        var pattern = /(^[0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]$)/;
        if (num.search(pattern) == -1)
            alert("Invalid");
        else {
            var pd = new Date();
            var bd = new Date();
            var df = num.split('-');
            bd.setFullYear(df[2], df[0], df[1]);
            if (bd < pd) {
                alert("Valid");
            }
            else {
                alert("DOB is lessthan Today");
            }
        }

    }

</script>