This method has been mentioned before. Here is only an example:
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title>使用attr()给指定的元素设置属性</title>
<script src="jquery-1.11.3.js"></script>
</head>
<body>
<ul id="fruit">
<li title="pg">苹果</li>
<li title="zj">橘子</li>
<li>香蕉</li>
</ul>
<script>
$(function(){
/*使用attr()给指定的元素设置style属性*/
$("li:eq(2)").attr("title","xj").attr("style","color:red;font-size:20px;");
});
</script>
</body>
</html>