<ul id="tab">
<li><a href="index.php">home</a></li>
<li><a href="article.php">article</a></li>
<li><a href="news.php">news</a></li>
</ul>

<script>
var keyword = 'article'; // 这里是程序传的关键词变量, PHP可以这么传 var keyword=<?=$keyword?>
var lis = document.getElementById('tab').getElementsByTagName('li');
switch(keyword){
    case 'article':
        lis[1].className = 'selected';
        break;
    case 'news':
        lis[2].className = 'selected';
        break;
    default:
        lis[0].className = 'selected'; // 默认为home
}
</script>

<script>
var lis = document.getElementById('tab').getElementsByTagName('li');
lis[2].className = 'selected';
</script>