第一种
<script language=javascript>
String.prototype.isDate = function()
{
   var r = this.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("2002-01-31".isDate());
alert("2002-01-41".isDate());
</script>

第二种
<script language=javascript>
String.prototype.isTime = function()
{
  var r = this.match(/^(\d{1,4})(-|\/)(\d{1,2})\2(\d{1,2}) (\d{1,2}):(\d{1,2}):(\d{1,2})$/);
  if(r==null)return false; var d = new Date(r[1], r[3]-1,r[4],r[5],r[6],r[7]);
  return (d.getFullYear()==r[1]&&(d.getMonth()+1)==r[3]&&d.getDate()==r[4]&&d.getHours()==r[5]&&d.getMinutes()==r[6]&&d.getSeconds()==r[7]);
}
alert("2002-1-31 12:34:56".isTime());
alert("2001-2-29 12:54:56".isTime());
alert("2002-1-41 12:00:00".isTime());
</script>

判断数字用 isNaN()