searchable dropdown with large dataset

[byka]

I have a data of more that 500000 records which want to search data and fill in dropdown list. I am using dropdown list its working buts it is very slow

<script type = "text/javascript">

    var ddlText, ddlValue, ddl, lblMesg;

    function CacheItems() {

        ddlText = new Array();

        ddlValue = new Array();

        ddl = document.getElementById("<%=ddlItems.ClientID %>");

        lblMesg = document.getElementById("<%=lblMessage.ClientID%>");

        for (var i = 0; i < ddl.options.length; i++) {

            ddlText\[ddlText.length\] = ddl.options\[i\].text;

            ddlValue\[ddlValue.length\] = ddl.options\[i\].value;

        }

    }

    window.onload = CacheItems;



    function FilterItems(value) {

        ddl.options.length = 0;

        for (var i = 0; i < ddlText.length; i++) {

            if (ddlText\[i\].toLowerCase().indexOf(value) != -1) {

                AddItem(ddlText\[i\], ddlValue\[i\]);

            }

        }

        lblMesg.innerHTML = ddl.options.length + " items found.";

        if (ddl.options.length == 0) {

            AddItem("No items found.", "");

        }

    }



    function AddItem(text, value) {

        var opt = document.createElement("option");

        opt.text = text;

        opt.value = value;

        ddl.options.add(opt);

    }

</script>

[F ES Sitecore]

If you're showing 500000 items then a dropdown is the wrong thing to use. Use an autocomplete textbox instead. Google for how to write one.