用JS弹出带确定和取消按钮的窗体

 <script type="text/jscript">
   function CheckProduct(){
                if (document.getElementById("txtOldPwd").value =="")
               {
                    document.getElementById("lblResult").innerText="旧密码不允许为空！";
                    return false;
                }
                else if (document.getElementById( "txtNewPwd").value=="")
                {
                    document.getElementById("lblResult").innerText = "新密码不允许为空!";
                    return false;
                }
                else if (document.getElementById( "txtNewPwd1").value=="")
                {
                    document.getElementById("lblResult").innerText = "确认密码不允许为空!";
                    return false;
                }
                else if ((document.getElementById( "txtNewPwd").value!=document.getElementById( "txtNewPwd1").value))
                {
                    document.getElementById("lblResult").innerText= "新密码和确认密码不一致!";
                    return false;
                }else
                {
                  if(confirm("你确信要修改吗？"))
                  {
                     return true;
                  }else
                  {
                    return false;
                  }
                }
  
}

   </script>

在页面里可以这样写

<asp:ImageButton ID="btnModify" OnClientClick="return CheckProduct()" runat="server" ImageUrl="~/Images/modify.jpg"  onclick="btnModify_Click1" />

也可以在后台这样调用

 this.btnModify.Attributes.Add("onclick", "return CheckProduct();");

这样在页面上点击修改按钮时就可弹出二次确定的窗体