AS3.0中怎么设定英文输入为12个字符串,中文6个汉字

文本输入框的设置，

import flash.events.Event;
function stringCut(msg:String, size:int):String
{
if (size < 2 && msg.charCodeAt(i) > 255) return "";

var reStr:String = "";
var addLength:int = 0;
for (var i:int = 0; i < size; i++)
{
msg.charCodeAt(i) > 255 ? addLength += 2:addLength += 1;
if (addLength <= size) reStr += msg.charAt(i);
else return reStr;
}
return reStr;
}

输入框.addEventListener(Event.CHANGE, inputTxt);
function inputTxt(e:Event):void
{
输入框.text = stringCut(输入框.text, 12);
}

let str = "00000000" str.characters.count