<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script src="./js/jquery.min.js"></script>
</head>
<body>
<ul>
<li>1</li>
<li class="item">2</li>
<li>3</li>
</ul>
<script>
$(function() {
//兄弟元素
$("ol .item").siblings("li").css("color", "red");
//第n个元素
//我们可以选择选择器选择
$("ul li:eq(2)").css("color", "blue");
})
//判断是否有类名
console.log($("div:first").hasClass("current"));
console.log($("div:last").hasClass("current"));
</script>
</body>
</html>