Allow numeric only in text box using javascript?

Allow numeric only in text box using javascript?

In Script File:

<script type="text/javascript">
    function allowNumericOnly(evt) {
        var charCode = (evt.which) ? evt.which : event.keyCode;
        if (charCode != 46 && charCode > 31
                && (charCode < 48 || charCode > 57))
            return false;

        return true;
    }
</script>

   
In Design Page:

    <asp:TextBox ID="txtAge" runat="server" onkeypress="return allowNumericOnly(event)"></asp:TextBox>