JavaScript实现下拉列表框可编辑功能

 
<script>
function clearOption(obj,e){
var currKey=0,e=e||event;
currKey=e.keyCode||e.which||e.charCode;
if(currKey == 8){
obj.options[0].text = "";
} 
} 
function writeSelect(obj,e){
var currKey=0,e=e||event;
currKey=e.keyCode||e.which||e.charCode;
obj.options[0].selected = "select";
if(currKey != 8){//此处旨在防止Firefox浏览器中出现乱码，注释该行可观察Firefox下的具体表现
obj.options[0].text = obj.options[0].text + String.fromCharCode(currKey);
} 
e.returnValue=false;
return obj.options[0].text;
} 
function ttt(){
var jg = document.getElementById("aa").options[document.getElementById("aa").selectedIndex].text;
//若在前置的writeSelect函数中同步设置options的value，则可直接在此处通过value获取
jQuery("#aa").empty();
jQuery("#aa").append("<option value=''></option>");
} 
</script>

 
<select style='width:150px;z-index:-1' id="aa" name="selectHelpCode" onkeydown="clearOption(this,event)" onkeypress="writeSelect(this,event)">
<option value=""></option>
<option value="11">11</option>
<option value="22">22</option>
<option value="33">33</option>
</select>
<input type="button" value="清除" onclick="ttt();"/>