                        課程
                    
                        /前端開發
                        
                            /JavaScript
                        
                        /DOM事件探秘

很困惑，檢查了好幾遍沒看出問題呢？大神求救

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>跨瀏覽器問題</title>
</head>

<body>

<div id="box">
<input type="button"? value="submit1" id="btn1">
<input type="button"? value="submit2" id="btn2">

</div>
<script>
var btn1=document.getElementById('btn1');
var btn2=document.getElementById('btn2');
function showmess(){
?? ?alert('you are my message');
?? ?}
var eventUtil={
?? ?addHandler:function(element,type,handler){
?? ?//DOM2 處理程序的方法
?? ?if(element.addEventListener){
?? ??? ?element.addEventListener(type,handler,false);
?? ??? ?}
?? ??? ?//IE 處理程序方法 ?
?? ?else if(element.attachEvent){
?? ??? ?element.attachEvent('on'+type,handler);
?? ??? ?}
?? ??? ?//DOM0處理事件程序判斷
?? ?else{
?? ??? ?element['on'+type]=handler;//觸發handler操作
?? ??? ?}
?? ?}
}

//刪除句柄
removeHandler:function(element,type,handler){
?? ?if(element.removeEventListener){
?? ??? ?element.removeEventListener(type,handler,false);
?? ??? ?}
?? ??? ?//IE事件處理程序
?? ?else if(element.detachEvent){
?? ??? ?element.detachEvent('on'+type,handler);
?? ??? ?}
?? ?else{
?? ??? ?element['on'+type]=null;
?? ??? ?}
?? ?}
eventUtil.addHandler(btn2,'click',showmess);
?? ?
</script>

</body>
</html>