小于选择器
jQuery( ":lt(index)" )
jQuery( ":lt(-index)" )
描述：选择所有小于指定下标的元素。
<!DOCTYPE html>
<html lang="zh-cn">
<head>
<meta charset="utf-8">
<title>lt demo</title>
<style>
</style>
<script
src="js/jquery-1.9.1.min.js"></script>
</head>
<body>
<table border="1">
<tr><td>TD
#0</td><td>TD #1</td><td>TD #2</td></tr>
<tr><td>TD #3</td><td>TD
#4</td><td>TD #5</td></tr>
<tr><td>TD #6</td><td>TD #7</td><td>TD
#8</td></tr>
</table>
<script>
$("td:lt(4)").css("backgroundColor","yellow");
$("td:lt(-2)").css("color","red");
</script>
</body>
</html>
原文：http://www.cnblogs.com/semcoding/p/3522832.html