Show Hide HTML DIV based on DropDownList condition using JavaScript in ASP.Net

Hi nauna,

Check this sample now and take its reference and correct your code.

HTML

<script type="text/javascript">
    function HowHideDiv() {
        var ddlValue = document.getElementById("DropDownList1").value;
        if (ddlValue == "Post") {
            document.getElementById("dvHours").style.display = "none";
        }
        else {
            document.getElementById("dvHours").style.display = "block";
        }
        return false;
    }
</script>
<form id="form1" runat="server">
<div>
    <asp:DropDownList runat="server" ID="ddlList">
        <asp:ListItem Value="Standard" Text="Standard" />
        <asp:ListItem Value="Post" Text="Post" />
    </asp:DropDownList>
    <br />
    <asp:LinkButton ID="lnkButton1" runat="server" Text="Show Hide" OnClientClick="return HowHideDiv()"></asp:LinkButton>
    <div id="dvHours">
        This is my hours
    </div>
</div>

Screenshot