node2:/var/www/html/jquery#cat t3.html
<htmL>
<head>
<title>aaa</title>
</head>
<body>
<h3>例子</h3>
<p title="选择你喜欢的水果.">你最喜欢的水果是?</p>
<ul>
<li id='aa'>苹果</li>
<li id='bb'>橘子</li>
<li id='cc'>菠萝</li>
<li id='dd'>雪梨</li>
</ul>
<script type="text/javascript" src="jquery-2.2.2.min.js"></script>
<script type="text/javascript" src="t3.js"></script>
node2:/var/www/html/jquery#
node2:/var/www/html/jquery#cat t3.js
var domObj = document.getElementById("aa"); //获得DOM对象 获取id=aa的元素
console.log(domObj.innerHTML);