Validate required fields in asp.net using javascript

 /////////////////////html
 
<table class="mt-3">
                    <tr>
                        <td>Name
                        </td>
                        <td>
                            <asp:TextBox ID="txtName" runat="server"></asp:TextBox>
                            <asp:RequiredFieldValidator ID="Required_txtName" runat="server" ValidationGroup="TestGrp"
                                ControlToValidate="txtName" Display="Dynamic" ErrorMessage="Required"
                                ForeColor="Red" SetFocusOnError="true"></asp:RequiredFieldValidator>
                        </td>
                    </tr>
                    <tr>
                        <td>Salary
                        </td>
                        <td>
                            <asp:TextBox ID="txtSalary" runat="server"></asp:TextBox>
                            <asp:RequiredFieldValidator ID="Required_txtSalary" runat="server"
                                ControlToValidate="txtSalary" Display="Dynamic" ErrorMessage="Required" ValidationGroup="TestGrp"
                                ForeColor="Red" SetFocusOnError="true"></asp:RequiredFieldValidator>
                        </td>
                    </tr>
                    <tr>
                        <td>Department
                        </td>
                        <td>
                            <asp:DropDownList ID="ddl_Dept" runat="server">
                                <asp:ListItem Value="0">-- Select --</asp:ListItem>
                            </asp:DropDownList>
                            <asp:RequiredFieldValidator ID="Required_ddl_Dept" runat="server" ValidationGroup="TestGrp"
                                ControlToValidate="ddl_Dept" Display="Dynamic" InitialValue="0"
                                ErrorMessage="Required" ForeColor="Red" SetFocusOnError="true"></asp:RequiredFieldValidator>
                        </td>
                    </tr>
                    <tr>
                        <td></td>
                        <td>
                            <asp:Button ID="btnSubmit" runat="server" Text="Sumbit" ValidationGroup="TestGrp" OnClientClick="return Validate_RequiredFiled_Save('TestGrp');" />
                        </td>
                    </tr>
                </table>

=========================  JS

function Validate_RequiredFiled_Save(groupName) {
                    if (typeof (Page_ClientValidate) == 'function') {
                        return Page_ClientValidate(groupName);;
                    }
                    if (Page_IsValid) {
                        alert(groupName + "successful");
                        //do something
                    }
                }
========================= Result