Javascript Date comparison and Check Numaric Browser Compatabulity

<script type="text/javascript" language="javascript"> 
         function CheckDates(source, arguments)
       {      
             var date1= document.getElementById('<%= txtfromDate.ClientID %>').value;
            var date2= document.getElementById('<%= txttoDate.ClientID %>').value;  
           var frmdates=date1.split('/')[1]+'/'+date1.split('/')[0]+'/'+date1.split('/')[2];
           var Todates=date2.split('/')[1]+'/'+date2.split('/')[0]+'/'+date2.split('/')[2];      
          varSanctionedDate=new Date(frmdates);
          varEndDate=new Date(Todates);           
            if(varSanctionedDate > varEndDate) 
                 arguments.IsValid = false;
            else
                 arguments.IsValid = true;
     }    
    </script>
<asp:CustomValidator ID="CVEndDate" runat="server" ValidationGroup="Save" ErrorMessage="To Date must be greater than End Date."
                                                    ControlToValidate="txttoDate" ClientValidationFunction="Check" ValidateEmptyText="false">&nbsp;</asp:CustomValidator>

function CheckNumeric(e)
        {
            var key
            if (window.event)
                key = event.keyCode
            else
                key = e.which                       
            if (key > 47 && key < 58 || key == 8)
                return;
            else
                if (window.event) //IE
                window.event.returnValue = null; else //Firefox
                e.preventDefault();
        }
Calling Method in TextBox : onkeypress="return CheckNumeric(event)"