可以添加自定义的Select控件

1.控件dom

<select name="WebSiteTarget" id="WebSiteTarget" class="w1" onchange="editable2(this);">

    <option value="-1">请选择城市</option>

    <option>福州</option>

    <option>厦门</option>

    <option>南平</option>

    <option value="0">(自定义输入)</option>

</select>

2.脚本

<script>

    function editable2(dom) {

        if (dom.value == "0") {

            var newvalue = prompt("请输入", "");

            if (newvalue) {

                addSelected(dom, newvalue, newvalue);

            }

        }

    }

    function addSelected(fld1, value1, text1) {

        if (document.all) {

            var Opt = fld1.document.createElement("OPTION");

            Opt.text = text1;

            Opt.value = value1;

            fld1.options.add(Opt);

            Opt.selected = true;

        } else {

            var Opt = new Option(text1, value1, false, false);

            Opt.selected = true;

            fld1.options[fld1.options.length] = Opt;

        }

    }

</script>

3.效果