Asp.net textbox control hide on postback

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C#

Javascript

ASP.NET4

I written code for getting textbox visible true dynamically using javascript

I am getting the textbox when i select 'others' in dropdown

when there is postback the textbox disappears

How to display the textbox with values after postback
below is my source code

        function ddlChanged(ddl) {
            if (ddl.value == "4") {
                document.getElementById('<%=txt_reason.ClientID %>').removeAttribute("disabled");               
                document.getElementById('<%=div_otherreason.ClientID %>').style.visibility='visible';
                document.getElementById('<%=div_otherreason.ClientID %>').style.display = 'block';
            }
            else {
                document.getElementById('<%=txt_reason.ClientID %>').setAttribute("disabled", true);
                document.getElementById('<%=txt_reason.ClientID %>').value = '';
                document.getElementById('<%=div_otherreason.ClientID %>').style.visibility='hidden';                
            }
        }
        ddlChanged(document.getElementById('<%=ddlReason.ClientID %>'));
    


<div class="col-md-4">
                                <span style="font-size: large; color: rgba(139, 0, 0, 1)">Select reason to Hold the Records|</span>
                                <div class="form-group">
                                    <asp:dropdownlist id="ddlReason" runat="server" cssclass="form-control" onchange="ddlChanged(this)">
                                        <asp:listitem value="0">--Select Reason--
                                        <asp:listitem value="1">Beneficiary Expired
                                        <asp:listitem value="2">Member Already Beneficiary                                        
                                        <asp:listitem value="3">Others
                                    
                                </div>
                            </div>

                            <div class="col-md-4" id="div_otherreason">
                                <span style="font-size: large; color: rgba(139, 0, 0, 1)">Enter Other reason Here |</span>
                                <div class="form-group">
                                    <asp:textbox id="txt_reason" runat="server" cssclass="form-control" autocomplete="off">
                                </div>
                            </div>

                            <div class="col-md-4">
                                <asp:button id="btn_Hold" runat="server" text="Click Here for Hold" cssclass="btn btn-danger" onclientclick="ShowLoading();" onclick="btn_Hold_Click" style="margin-top: 25px">
                            </div>

What I have tried:

I tried every possiblity, but not getting the solution, i need to div_otherreason will be visible after postback