Simple Dynamic ComboBox

[jstfsklh211]

<script type="text/javascript">
//<![CDATA[
    function cbUpdate()
    {
        var opt;
        var sel = document.info.cbShow;
        sel.style["display"] = "block";
        sel.length = 0;

        opt = document.createElement( "option" );
        opt.setAttribute("value", "0");
        optTxt = document.createTextNode(document.info.cbSelected.value);
        opt.appendChild(optTxt);
        sel.appendChild(opt);

        for(i = 0; i < document.info.cbHold.length; i++)//or use ajax
        {
            if ((document.info.cbHold[i].text).indexOf(document.info.cbSelected.value) != -1)
            {
                opt = document.createElement( "option" );
                opt.setAttribute("value", document.info.cbHold.options[i].value);
                optTxt = document.createTextNode(document.info.cbHold.options[i].text);
                opt.appendChild(optTxt);
                sel.appendChild(opt);
            }
        }
    }
    function cbSelect()
    {
        var sel = document.info.cbShow;
        document.info.cbSelected.value = sel.options[sel.selectedIndex].text;
        sel.style["display"] = "none";
    }
//]]>
</script>
<div class="comboBox" style="width: 150px;">
    <input type="text" name="cbSelected" id="cbSelected" style="width: 150px;"
           onfocus="cbUpdate(this.id)" onkeyup="cbUpdate(this.id)"/><br/>
    <select class="cbInput" name="cbShow" id="cbShow" size="5" style="width: 154px; position: absolute; display: none;"
            onchange="cbSelect()" onfocus="cbUpdate()"></select>
    <select class="cbInput" name="cbHold" id="cbHold" style="display:none;">
        <option value="1">aa</option>
        <option value="2">ab</option>
        <option value="3">ac</option>
        <option value="4">bc</option>
        <option value="5">bd</option>
        <option value="6">be</option>
        <option value="7">ba</option>
        <option value="8">cc</option>
        <option value="9">cd</option>
        <option value="10">ce</option>
        <option value="11">ca</option>
    </select>
</div>

thoughts? opinions?