                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /DOM事件探秘

哪里错了？禁止跳转和阻止冒泡

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<script type="text/javascript">
function btnMessage(){
   alert("hello world1");
   }
function btnMessage2(event){
   alert(event.type);
   }
function btnMessage3(event){
   event.stopPropagation();
   event.pretDefavenult();
   }
window.onload = function(){
var btn2 = document.getElementById("btn2");
var btn3 = document.getElementById("btn3");
var box = document.getElementById("box");
var btn4 = document.getElementById("btn4");
btn2.onclick = function(){
   alert("hello world0");
   }
box.onclick = function(){
   alert("hello world00");
   }

//btn2.onclick = null;
//btn3.addEventListener('click',function(){alert(this.value);},false);
//btn3.removeEventListener('click',btnMessage,false);
//btn3.attachEvent('onclick',btnMessage);
    var UntilHandler={
   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;
       }
   },
   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] = null;
       }
   }
   }
   UntilHandler.addHandler(btn3,'click',btnMessage2);
   UntilHandler.addHandler(bnt4,'click',btnMessage3);
    //UntilHandler.removeHandler(btn3,'click',btnMessage2);

}
</script>
</head>
<body>
   <div id = "box">
        <input type="button" name="btn" value="按钮" onclick="btnMessage()">
        <input type="button" name="btn2" value="按钮2" id="btn2">
        <input type="button" name="btn3" value ="按钮3" id= "btn3">
        <a href= "http://www.imooc.com/course/programdetail/pid/32" id = "btn4">跳转</a>
    </div>
<script>
</script>
</body>
</html>