How to fetch the data returned from javascript function to server side in ASP.NET via C#?

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C#

ASP.NET

Javascript

I want to fetch the data returned from javascript function to server side in asp.net via c#. Since I need data from Database I am invoking the JS Function to generate a Confirmation Box in server side event under button click. But on clicking OK/Cancel button of the Confirmation Box I am not able to get the data from the hidden field set in the javascript function to server side.

What I have tried:

Javascript Function

//var confirm_value = document.createElement("INPUT");
//   confirm_value.type = "hidden";
//   confirm_value.name = "confirm_value";
var control = '<%=inpHide.ClientID%>';
if (confirm(objMsg)) {
    alert(1);
    document.getElementById(control).value = "1";
    //confirm_value.value = "1";
    return true;
}
else {
    alert(0);
    document.getElementById(control).value = "0";
    //confirm_value.value = "0";
    return false;
}

Code Behind
under button click event

string AlertMessage = "Next Working Day Is On " + NextBusinessDate + " Do You Want To Continue?";
this.ClientScript.RegisterStartupScript(typeof(Page), "Popup", "ConfirmApproval('" + AlertMessage + "');", true);
string confirmValue = inpHide.Value;