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

為什么按鈕點擊了都沒用

<!DOCTYPE?html>
<html>
?<head>
??<meta?charset="UTF-8">
??<title></title>
?</head>
?<body>
??<div?>
???<input?type="button"?value="按鈕2"?id="btn2"/>
???<input?type="button"?value="按鈕3"?id="btn3"/>
??</div>
??
??<script>
???function?showMes(){
????alert("hello?world!")
???}
???var?btn2=document.getElementById('btn2');
???var?btn3=document.getElementById('btn3');
???btn2.onclick=function(){
????alert("這是通過DOM0級添加的事件");
???}
???//跨瀏覽器處理程序
???var?eventUtil={
????//添加句柄
????addHandler:function(element,type,handler){
?????if(element.addEventListener){
??????element.addEventListener(type,handler,false);
?????}else?if(element.attachEvent){
??????element.attachEvent('on'+type,handler);
?????}else{
??????element['on'+type]=handler;
?????}
????}
????//刪除句柄
????removeHandler:function(element,type,handler){
?????if(element.removeEventListener){
??????element.removeEventListener(type,handler,false);
?????}else?if(element.detachEvent){
??????element.detachEvent('on'+type,handler);
?????}else{
??????element['on'+type]=handler;
?????}
????}
???}
???eventUtil.addHandler(btn3,'click',showMes);
??</script>
?</body>
</html>