getAttribute：取得属性；
setAttribute：设置属性；
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Untitled Document</title>
<script language="JavaScript">
function change() {
var input = document.getElementById("li1");
alert(input.getAttribute("title"));
input.setAttribute("title", "mgc");
alert(input.getAttribute("title"));
}
</script>
</head>
<body>
<ul id="u">
<li id="li1" title="hello">Magci</li>
<li>J2EE</li>
<li>Haha!</li>
</ul>
<input type="button" value="Change" onClick="change();" />
</body>
</html>