怎么会弹出两个数值？

var EventUtil={

addHandler:function(element,type,handler){

//绑定事件

if(element.addEventListener){

element.addEventListener(type,handler,false);

}else if(element.attachEvent){

element.attachEvent("on"+type,handler);

}else{

element["on"+type]=null;

}

},

removeHandler:function(element,type,handler){

//移除事件

if(element.removeEventListener){

element.removeEventListener(type,handler,false);

}else if(element.detachEvent){

element.detachEvent("on"+type,handler);

}else{

element['on'+type]=null;

}

},

getTarget:function(event){

return event.target||event.srcElement;

},

preventDefault:function(event){

if(event.preventDefault){

event.preventDefault();

}else{

event.returnValue=false;

}

},

stopPropagation:function(event){

if(event.stopPropagation){

event.stopPropagation();

}else{

event.cancelBubble=true;

}

}

}

EventUtil.addHandler(window,"scroll",function(event){

alert(document.documentElement.scrollTop)

})