Filter Auto Suggestion Feature in ASP.NET Dropdown List View

This post will describe how to use ASP.Net's filtering feature to receive auto suggestions from a dropdown list view. The data will be loaded from the script side and the Dropdown view asp:DropDownList tag will be used. The client-side dropdown view suggestion will be obtained with the aid of JavaScript's 'onkeyup' events. The following is an example markup page using javascript code.

Markup page

<asp:Content ID="BodyContent" ContentPlaceHolderID="MainContent" runat="server"><main>
    <script type="text/javascript">
        function filterDropdown() {
            var input, filter, dropdown, options, i;
            input = document.getElementById("txtSearch");
            filter = input.value.toUpperCase();
            dropdown = document.getElementById("<%= ddlOptions.ClientID %>");
             options = dropdown.getElementsByTagName("option");
             for (i = 0; i < options.length; i++) {
                 if (options[i].textContent.toUpperCase().indexOf(filter) > -1) {
                     options[i].style.display = "";
                 } else {
                     options[i].style.display = "none";
                 }
             }
         }
    </script>
            <div>
            <label for="txtSearch">Search:</label>
                <input type="text" id="txtSearch" onkeyup="filterDropdown()" placeholder="Search options..." />
            <asp:DropDownList ID="ddlOptions" runat="server">
                <asp:ListItem Text="Option" Value="Select"></asp:ListItem>
                <asp:ListItem Text="Option 1" Value="1"></asp:ListItem>
                <asp:ListItem Text="Option 2" Value="2"></asp:ListItem>
                <asp:ListItem Text="Option 3" Value="3"></asp:ListItem>
                <asp:ListItem Text="Option 4" Value="4"></asp:ListItem>


            </asp:DropDownList></div>

    </main>
</asp:Content>

Server end page

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    ' No server-side logic needed for this example.
    If Not IsPostBack Then
        ddlOptions.Items.Clear()
        ddlOptions.Items.Add(New ListItem("aaa", "1"))
        ddlOptions.Items.Add(New ListItem("bbb 2", "2"))
        ddlOptions.Items.Add(New ListItem("ccc 3", "3"))
        ddlOptions.Items.Add(New ListItem("dd 4", "4"))
    End If
End Sub

Output

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