.children()的父子问题
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8" />
<title></title>
<link rel="stylesheet" href="imooc.css" type="text/css">
<style>
.left {
width: auto;
height: 120px;
}
.left div {
width: 150px;
height: 70px;
padding: 5px;
margin: 5px;
float: left;
background: #bbffaa;
border: 1px solid #ccc;
}
a {
display: block;
}
</style>
<script src="http://lib.sinaapp.com/js/jquery/1.9.1/jquery-1.9.1.min.js"></script>
</head>
<body>
<h2>children方法()</h2>
<div class="left first-div">
<div class="div">
<ul class="level-1">
<li class="item-1">1</li>
<li class="item-2">2</li>
<li class="item-3">3</li>
</ul>
</div>
<div class="div">
<ul class="level-2">
<li class="item-1">1</li>
<li class="item-2">2</li>
<li class="item-3">3</li>
</ul>
</div>
<div class="div">
<ul class="level-3">
<li class="item-1">1</li>
<li class="item-2">2</li>
<li class="item-3">3</li>
</ul>
</div>
</div>
<button id="bt1">点击：children无参数</button>
<button id="bt2">点击：children传递表达式</button>
<script type="text/javascript">
$("#bt1").click(function() {
$('.left first-div').children().css('border', '3px solid red')
})
</script>
<script type="text/javascript">
$("#bt2").click(function() {
//找到所有class=div的元素
//找到其对应的子元素ul，然后筛选出最后一个，给边宽加上颜色
$('.div').children(':first').css('border', '3px solid blue')
})
</script>
</body>
</html>要完成【找到所有class=div的元素节点，然后找到其对应的子元素，并且加上一个红色边框
】此要求 为什么第60行不能这样写 而要写成
$('.div').children().css('border', '3px solid red')
