How to get the value in code behind when setting the textbox value through javascript

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ASP.NET

Javascript

Hello,
I am setting the textbox value through javascript code but when i am trying to fetching that value from textbox to database it is not getting anything..when i debug the code the check command parameter value its empty.Please tell me how can i do this..

using (SqlCommand cmd = new SqlCommand("insertTrusteeInfoSP", con))
{
    cmd.CommandType = CommandType.StoredProcedure;
    //cmd.Parameters.AddWithValue("@TrusteeInformationId", Convert.ToInt32(txtEmployeeId.Text));
    cmd.Parameters.AddWithValue("@EmployeeReferenceId", txtlinemanager.Text);
    cmd.Parameters.AddWithValue("@TrusteeName", txtTrusteeName.Text.);
    //cmd.Parameters.AddWithValue("@TrustInformationId", Session["TrustInformationId"].ToString());
    // cmd.Parameters.AddWithValue("@TrustInformationId", Session["TrustInformation"].ToString());
    if (chkIsDefaultSign.Checked)
    {
        cmd.Parameters.AddWithValue("@IsDefaultSignatory", true);
    }
    else
    {
        cmd.Parameters.AddWithValue("@IsDefaultSignatory", false);
    }
    if (CheckIsActive.Checked)
    {
        cmd.Parameters.AddWithValue("@IsActive", true);
    }
    else
    {
        cmd.Parameters.AddWithValue("@IsActive", false);
    }
    cmd.Parameters.AddWithValue("@Description", txtdescription.Text);
    con.Open();
    result = cmd.ExecuteNonQuery();
    con.Close();

My javascript code

<script type="text/javascript">
        function OpenPopup(showPopupFor) {
            var popupGenerator = null;
            var trusteeName = null;
            popupGenerator = document.getElementById("<%= txtlinemanager.ClientID %>");
            trusteeName = document.getElementById("<%= txtTrusteeName.ClientID %>");


            if (popupGenerator == null) return false;
            var url = employeesearch.aspx";
            var params = new Array(popupGenerator.Value);
            var popupSetting = "center:yes;scroll:no;edge=raised;status:no;resizable:no;dialogWidth:400px;dialogHeight:415px";
            var prevReturnValue = window.returnValue;
            window.returnValue = undefined;
            var pmx = window.showModalDialog(url, params, popupSetting);
            if (pmx == undefined) {
                pmx = window.returnValue;
            }
            window.returnValue = prevReturnValue;
            if (pmx == undefined || pmx == null) {
                popupGenerator.value = "";
            }
            else {
                // popupGenerator.value = pmx.toString();
                popupGenerator.value = pmx[0].toString();
                trusteeName.value = pmx[1].toString();
            }
            //popupGenerator.focus();
            return false;
        }

    </script>

on running on browser value is being shown in txtlinemanager textbox but when i am adding this value on command parameters it shows empty.