javascript控制文本框只能输入数字

<script language="javascript">
   function isnum()
     {
        if(event.keyCode<48||event.keyCode>57)
        {
            event.keyCode=0;
        }
     }
   function lblnum()
     {
            document.all.lblnum.innerText = "";
            document.all.lblnum.innerText = (document.all.txtNum.value * 0.1).toFixed(2) + "元";
     }
</script>

<asp:textbox onkeypress="isnum();" id="txtNum" onkeyup="lblnum();" runat="server" Width="56px" cssClass="longinput"></asp:textbox> 
    <DIV id="lblnum" style="DISPLAY: inline; HEIGHT: 15px" ms_positioning="FlowLayout"></DIV>

只为个人保留经验所用