javascript numeric validation problem

Sometimes tab is not working got hang in between when i tried to type in textbox also not able to copy paste Here is my code:- <script type = "text/javascript">               var isShift=false;         function Numeric(keyCode)             {             if(keyCode==16)             isShift = true;             //numbers,tab,delete,backpace etc             return ((keyCode >= 48 && keyCode <= 57 || keyCode == 8 || keyCode == 9 || keyCode==46 || (keyCode >= 96 && keyCode <= 105 || keyCode>=32 && keyCode<=46)) && isShift == false);               }                   </script>       and calling in textbox.   <asp:TextBox ID="txtLNo1" onkeydown  = "return Numeric(event.keyCode);" runat="server"></asp:TextBox>