How to make Div visibility based on condition using JavaScript in ASP.Net

hi

see below code: 

<div id="message" class="backS2fT">
    <script type="text/javascript">
        function WebForm_OnSubmit() {
            var message = document.getElementById("message");
            message.style.display = "none";
            if (typeof (ValidatorOnSubmit) == "function" && ValidatorOnSubmit() == false) {
                for (var i in Page_Validators) {
                    try {
                        if (!Page_Validators[i].isvalid) {
                            message.style.display = "block";
                        }
                    } catch (e) {
                    }
                } return false;
            } return true;
        }
    </script>
</div>
<div id="sendmessageT" runat="server" visible="false">
</div>

according above code when click  button if users doesn't fill textboxs in page it will dispaly <div id="messge"> now I want when users click on button if they doesn't fill textboxs at first it does sendmessageT.visibility=false after that display <div id="message">

Best regards

neda