Cannot read property 'nodeType' of - javascript吧

level 1

Cannot read property 'nodeType' of undefined为什么会报这个错
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="res/jquery/jquery-1.8.3.min.js"></script>
<title>导航条</title>
<meta charset="utf-8" />
<style type="text/css">
*,body{
padding:0;
margin:0;
}
.main{
width:550px;
height:60px;
}
#list{
width:550px;
height:60px;
display:flex;
justify-content:center;
list-style-type:none;
}
.n1{
background-color:#ff89b2;
color:#FFF;
text-align:center;
line-height:60px;
font-size: 14px;
width:79px;
}
.active{
background-color:#ff4988;
color:#FFF;
text-align:center;
line-height:60px;
font-size: 14px;
width:79px;
}
</style>
</head>
<body>
<div class="main">
<ul id='list'>
<li class='n1'>浪漫爱情</li>
<li class='n1'>商务鲜花</li>
<li class='n1'>精选礼品</li>
<li class='n1'>花卉绿植</li>
<li class='n1'>精品蛋糕</li>
<li class='n1'>浪漫花束</li>
<li class='n1'>卡通花束</li>
</ul>
</div>
<script type="text/javascript" defer="defer">
$(document).ready(function(){
$(".n1").mouseover(function(){
$(this).attr("class","active")
});
$(".n1").mouseout(function(){
$(this).attr("class","n1")
});
})
</script>
</body>
</html>

2020年11月19日 02点11分 1

level 1

朝鲜农业部部长楼主

有明白的老歌吗

2020年11月19日 02点11分 2