Must be longer than 7 characters, first (two) digit(s) NOT greater than 12, second (two) digit(s) NOT greater than 31 and last 4 greater than 1900

<script language="javascript">
<!--
function v()
{
    a=document.frmDate.dt.value;
    if (eval('a.length>7&&!(a.split("/")[0]*1>12)&&!(a.split("/")[1]*1>31)&&!(a.split("/")[2]*1<1900)'))
        alert('ok');
    else
        alert('invalid');
}
//-->
</script>