限制鍵盤輸入

function KeyFilter(type)
{
 var berr=false;
 
 switch(type)
 {
  case ''date'':
   if (!(event.keyCode == 45 || event.keyCode == 47 || (event.keyCode>=48 && event.keyCode<=57)))
    berr=true;
   break;
  case ''number'':
   if (!(event.keyCode>=48 && event.keyCode<=57))
    berr=true;
   break;
  case ''cy'':
   if (!(event.keyCode == 46 || (event.keyCode>=48 && event.keyCode<=57)))
    berr=true;
   break;
  case ''long'':
   if (!(event.keyCode == 45 || (event.keyCode>=48 && event.keyCode<=57)))
    berr=true;
   break;
  case ''double'':
   if (!(event.keyCode == 45 || event.keyCode == 46 || (event.keyCode>=48 && event.keyCode<=57)))
    berr=true;
   break;
  default:
   if (event.keyCode == 35 || event.keyCode == 37 || event.keyCode==38)
    berr=true;
 }
 return !berr;
} 

<input type="text" id="tb_tag" runat="server" onkeypress="return KeyFilter(''double'');" />