gridview 中textbox 的判断

前台源码为：
  <asp:GridView id="gvNeedDrugs" runat="server"  Width="100%" AutoGenerateColumns="False">
    <Columns>
        <asp:BoundField DataField="jzd_id" ></asp:BoundField>
        <asp:BoundField HeaderText="名称" DataField="jzd_name" ></asp:BoundField>
        <asp:BoundField HeaderText="规格" DataField="jzd_guige" ></asp:BoundField>
        <asp:BoundField HeaderText="厂家" DataField="jzd_factory" ></asp:BoundField>
        <asp:BoundField HeaderText="所需数量" DataField="jzd_needno" ></asp:BoundField>
        
        <asp:BoundField HeaderText="单价" DataField="Jzd_onemoney" />
        <asp:TemplateField>
            <HeaderTemplate>
                捐助数量
            </HeaderTemplate>
            <ItemTemplate>
            
               <asp:TextBox ID="TextBox1" runat="server" Width="90px" Text="0" onclick="this.value=''" onBlur=""            
      onKeyUp="this.value=this.value.replace(/\D/g,'');" onafterpaste="this.value=this.value.replace(/\D/g,'');"></asp:TextBox>
            
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField HeaderText="已捐数量" DataField="jzd_nowno" ></asp:BoundField>
    </Columns>
    <HeaderStyle CssClass="tb_sxyp"  />
</asp:GridView>
   实现的功能是：
   在textbox 输入捐助数量后，判断此值是否大于所需数量-已捐数量，否则提示错误。重新输入。在触发onBlur事件时怎么编写js ？