请教:日期的输入判断

<script language=javascript>
function isDate(str)
{
   var r = str.match(/^(\d{1,4})(-|\/)(\d{1,2})\2(\d{1,2})$/); 
   if(r==null)return false; var d = new Date(r[1], r[3]-1, r[4]); 
   return (d.getFullYear()==r[1]&&(d.getMonth()+1)==r[3]&&d.getDate()==r[4]);
}
alert(isDate("2002-01-31"));
alert(isDate("2002-01-41"));
</script>