How to add javascript validation event to textbox inside Gridview?

javascript function to restrict user to type only numbers in textbox.
Code:
<script type = "text/javascript" language = "javascript">
            function numeralsOnly(evt)
            {
                evt = (evt) ? evt : event;
                var charCode = (evt.charCode) ? evt.charCode : ((evt.keyCode) ? evt.keyCode : ((evt.which) ? evt.which : 0));
                if (charCode > 31 && (charCode < 48 || charCode > 57) && (charCode != 46))
                {
                    alert("Enter numerals only in this field!");
                    return false;
                }
                return true;
            }
       </script>

the way in which it can be specified with a textbox inside a gridview:
<asp:TextBox ID="txtProjBudget" onkeypress="return numeralsOnly(event)" runat="server"  Text='<%# Eval("Proj_Exp") %>' Width="103px"></asp:TextBox>