Store javascript return value of a function to the respective Asp Control OnClick event at server side

<asp:Button ID="Button1" runat="server" Text="Lunch" CausesValidation="false" CssClass="bigbuttons" style="background:url(../App_Themes/Images/green-box.gif)" Font-Bold="True"  ForeColor="White" Font-Size="Large" OnClientClick="openmodalWin(); return false;"  /> <br />

JavaScript:-

function openmodalWin() {
        var CloseTImeOfPopUp = window.showModalDialog("ClockPopUP.aspx", "Clock", "dialogWidth:550px;dialogHeight:350px,");
        }

As you can see that i m calling a javascript function "openmodalWin" on the Button Click event .I had checked that the function is returning CloseTimeofPopUp sucessfully and i am able to display it via Alert box. I want that the reurn value from the javascript function, i can store on the same server side code i.e. Button1_OnClick() event and then i can store it to database. Please tell me how i can do this ?

Tags: C#, Javascript, ASP.NET